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Fibers as Structural Element for the Reinforcement of Concrete. Technical Manual

Manual beton armat cu fibre

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Page 1: Manual beton armat cu fibre

F i b e r s a s S t r u c t u r a l E l e m e n t f o r t h eR e i n f o r c e m e n t o f C o n c r e t e .

Officine Maccaferri S.p.A.Via Degli Agresti, 6 40123 Bologna - ItaliaTel: +39 051 6436000 Fax: +39 051 236507e-mail: [email protected]

Maccaferri Canada Ltd.400 Collier MacMillan Dr. UnitB Cambridge, Ontario - [email protected]

Maccaferri Inc.10303 Governor Lane BlvdWilliamsport Maryland - United [email protected]©

Mac

cafe

rri d

o Br

asil

Ltda

.

Te c h n i c a l M a n u a l

Page 2: Manual beton armat cu fibre

1 - Introduction

2 - Fibers as structural element for the reinforcement of concrete

2.1 - Historical review of the technology of incorporating fi bers in concrete2.2 - Concept of reinforcement of concrete through fi bers2.3 - Fiber types – Classifi cation of current commercial fi bers in function of the raw material. Organic fi bers (natural and synthetic polymers) and inorganic fi bers (metallic)2.4 - Steel fi bers. Classifi cation upon geometrical, physical, chemical, mechanical char-acteristics and production process2.5 - Synthetic and natural fi bers. Classifi cation based upon geometric, physical,chemical, mechanical characteristics and production process2.6 - Current standard situation2.7 - List of MACCAFERRI’s fi bers. Classifi cation of MACCAFERRI’s fi bers

3 - Fiber reinforced concrete; Basic elements for the structural project

3.1 - Mechanical characterization of fi ber reinforced concrete. Most importantresistant features3.2 - Structural compatibility of fi ber reinforced concrete elements3.3 - Instructions for the design of fi ber reinforced concrete frameworks3.4 - Current standard situation

4 - Design and detailed considerations for concrete mixtures;advice for fi bers incorporation into the mixture

4. 1 - Concrete, technological aspects for its formulation4.2 - Advice for the incorporation of fi bers in concrete4.3 - Advice for insertion of fi bers into concretes for prefabricated elements4.4 - Recommendations for the use of fi bers into wet and dry sprayed concretes4.5 - Concrete admixtures and their compatibility of use in fi ber reinforced concrete4.6 - Typical applications of the structural and not structural fi ber reinforced concrete4.7 - Current standard situation

5 - Applications of fi ber-reinforced concrete: tunnels, designof the pre-lining and of the fi nal lining

5.1 - Conventionally bored tunnels and tunnels excavated through TBM5.2 - Design criteria for tunnel supports and linings5.3 - Design of supporting structures made of fi ber-reinforced shotcrete5.4 - Design of lining made of fi ber-reinforced concrete pumped on-site5.5 - Use of fi bers for fi re resistance of concrete. Description of fi ber mixes,structural and anti-spalling proposal for fi nal linings

INDEX

Page 3: Manual beton armat cu fibre

INDEX

5.5.1 - Objective of passive protection of concrete against fi re5.5.2 - Polypropylene and cellulose fi bers as passive protection of concreteagainst fi re5.6 - Quality control of fi ber-reinforced concrete in tunnels5.7 - Current standard situation

6 - Appliances in Fiber reinforced concrete. Floors design

6.1 - Industrial, harbour, airport, road, and special uses6.2 - Methodology of conventional design for fl oors6.3 - Design of joints in fl oors6.4 - Methods of fl oors design in fi ber reinforced concrete6.5 - Fiber reinforced concrete and the joints design6.6 - Control of quality in fi ber reinforced concrete for fl oorings6.7 - Current standard situation

7 - Applications of fi ber reinforced concrete: prefabricated elements

7.1 - The use of fi ber reinforcement in prefabricated/pre-cast concrete7.1.1 - Final remarks7.2 - Design of precast segment in fi ber reinforced concrete7.3 - Examples of applications. Padding panels, prestressed beams, non-structuralprefabricated elements7.3.1 - Closing panels7.3.2 - Double T covering prestressed beams7.3.3 - Structures for fl at coverings7.3.4 - Pre-casted stretched beams7.3.5 - Different elements7.4 - SFRC special applications7.4.1 - Foundation systems7.4.2 - New potential applications7.4.2.1 - Structures exposed to earthquakess7.4.3 - Flooring covering with metal shaped sheets or precast – metal deck

8. Measuring equipments for Wirand® fi bers

8.1 - Equipments for the introduction of fi bers into concrete8.2 - Measuring systems of fi bers for shot concrete8.3 - Measuring systems of fi bers for the production of ashlars8.4 - Measuring systems of fi bers for fl oorings concrete8.5 - Measuring systems of organic and polymeric fi bers8.6 - Circular batchers

Page 4: Manual beton armat cu fibre

INDEX

8.6.1 - Description of the machine8.6.2 - Aim8.6.3 - Typology8.6.4 - Principle of working8.6.5 - Principle of use8.6.6 - Technical data and main dimensions8.6.7 - Moving/conveyance8.6.8 - Necessary electric arrangement8.6.9 - Tools and implements necessary to the installation8.6.10 - Positioning8.6.11 - Feet fi xing8.6.12 - Eccentric masses adjustment8.6.13 - Welding operations8.6.14 - Fibers storage8.6.15 - Information to gather for the correct confi guration of the installation8.7 - Pneumatic batchers8.7.1 - Aim8.7.2 - Typology8.7.3 - Principle of working8.7.4 - Principle of use8.7.5 - DOSOBOX8.7.6 - SC99/28.7.7 - Special machines8.8 - Personalized machine

9 - Authors

10 - References

Page 5: Manual beton armat cu fibre

The purpose of this manual is to provide general information, criteria and new methodologies for the calculation, project and execution of concrete reinforced works with fibers. They will be presented, therefore, the obtained data of the investigations made by Maccaferri, oriented to the study of the behavior, resistance and efficiency of such structures.

The Maccaferri intention is to have new and useful contributions to concrete works reinforced with fibers, helping the consultants and contractors work who act in the segment of structural engineer-ing.

For a more detailed analysis on the arguments treated here, we suggest to consult the specific pub-lications that are indicated in the bibliographical references.This manual they will be presented and discussed theoretical foundations, numerical examples of the of the concrete reinforced with fibers applications and details of the use of the Wirand® metallic fibers and Fibromac® plastic fibers.

Maccaferri is placed to total disposition, to give solution to problems, cradle in its experience, acquired along more than 100 years of existence in all the world.

1 - Introduction.

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Page 6: Manual beton armat cu fibre

2 - Fibers as structural element for the reinforcement of concrete.

The presence of fibers having adequate tensile strength, and being homogeneously distributed

within concrete, builds a micro-scaffolding that, on the one side, demonstrates itself being ef-

ficient in counteracting the known phenomenon leading to crack formation due to shrinkage,

and, on the other side, leads the concrete’s ductility(1) to become increasingly relevant with

increasing strength of the fibers. This provides the concrete with a high toughness(2) as well.

As it is known, in the vast majority of currently applied calculation and verification rules, the

concrete’s tensile strength is generally neglected in the calculation route, given concrete’s brittle

behaviour. The use of a fiber-reinforced matrix makes it possible to stabilize tensile properties.

In this way, the tensile strength can be now be exploited as well between other mechanical

properties in the design phase. This highly relevant technical advantage will be reported in de-

tails in chapter 3 of the present publication.

Given operative difficulties, tensile tests are generally not realized onto the concrete directly.

The evaluation of tensile properties, as well as of ductility and toughness, are carried out indi-

2.2 - Concept of reinforcement of concrete through fibers.

2.1 - Historical review of the technology of incorporating fibers in concrete.

The idea of using a fibrous material to provide tensile strength to a material strong in compression

but brittle, looses itself in the mists of time; in ancient Egypt straw was added to clay mixtures

in order to provide bricks with enhanced flexural resistance, thus providing better handling

properties after the bricks had been dried in the sun.

Other historical cases of fiber reinforcement exist: plaster reinforced with horsehair, or again

with straw in the poorest building conditions, so as to avoid the unsightly occurrence of cracks

due to shrinkage, counter-ceilings made of plaster reinforced through reed canes, cement

conglomerates fiber-reinforced through asbestos, etc.

But the scientific approach to such a problem is definitely more recent.

First studies dealing with use of steel fibers and glass fibers in concrete date back to the 1950’s;

in the 60’s the first studies concerning fiber reinforced concrete using synthetic fibers appear.

Definition of fiber-reinforced concrete (Official Bulletin CNR n.166 part IV):

“The purpose of the utilization of fibers within a cement matrix is the formation of a composite

material in which the conglomerate, which can already be considered as a composite material

that is composed by a litic scaffold dispersed in a matrix of hydrate cement paste, is combined

with a reinforcing agent that is made of fibrous material of various nature”.

(1) Ductility is the ability of a material to stand considerable deformation thereby maintaining good resistance.(2) Toughness is the ability of a material to counteract crack propagation by dissipating deformation energy.

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Page 7: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

rectly through bending tests on beams or sheets, as it will be reported in details in the following

sections.

Graphic 2.1 shows qualitatively the possible outcomes which can be obtained from bending

tests on fiber-reinforced concrete elements through graphs reporting load vs. crack formation

or load vs. deflection.

Under the incidence of moderate loads, below breaking loads for concrete, the material’s be-

haviour is always elastic and no fracture is produced in the specimen during the bending test,

independently from the presence or the quality and quantity of fibers. In contrast, considerably

different behaviours can occur in continuing the test, thus increasing the applied load departing

from point A, called “first-crack point”:

Graphic 2.1 – Bending tests.

Deflection

Load

Elastic phase Non-elastic phase

First-

crack

point

- Curve I depicts the behaviour of a traditional concrete without reinforcement. Since

the structure is isostatic (the beam is simply supported at both ends), it collapses immediately

after first-crack loading is reached, such as typically occurring for brittle materials.

- Curve II shows some ability of the (fiber-reinforced) concrete to absorb, departing from

the first-crack point, a certain although low load (A-B) through a progressive slower collapse

(degrading behaviour).

- Curve III, in contrast, is typical of a ductile material, and shows a concrete able to sus-

tain, departing from the first-crack point, a considerable deflection (A-B) under constant load,

still before the even slower occurrence of collapse (plastic behaviour).

- Curve IV finally highlights even an increment in the tolerable load under a wide deflec-

tion (A-B) after the first-crack point (hardening behaviour).

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Page 8: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

It is evident that all these possible behaviours, or different ductility and toughness levels ac-

quired by the concrete, depend both from the quantity of the present fibers as well as from

their mechanical, and geometrical characteristics.

Considering the influence of the fiber geometry on the behaviour of FRC(3) and of SFRC(4),

although any aspect is relevant, it is the relationship between the fiber length and equivalent

diameter (L/D named aspect ratio or slenderness ratio) which is considered as the most charac-

terising element, since ductility and toughness of a fiber-reinforced concrete depend in large

measure on its value (Graphic 2.2).

Equally important are the mechanical characteristics of fibers, and, between them, tensile

strength essentially. Tensile strength plays a fundamental role on the behaviour of FRC and of

SFRC as the hindered pull out, which is due to the real and the forced adherence between fiber

and concrete (Graphic 2.3), can lead to fiber breakage caused by insufficient tensile strength

(Graphic 2.4).

(3) CRF = Fiber reinforced concrete(4) CRFA = Steel fiber reinforced concrete

Graphic 2.2 – Absorbed energy vs aspect ratio.

Abso

rved

ener

gy(%

)

Aspect ratio ( )L/D

Graphic 2.3 – Increase in the adherence fiber-concrete with fiber shape.

Pull -

out lo

ad

Fibra Reta Fibra com Ancoragem

DisplacementDisplacement

Pull-

outlo

ad

Straight fiber Hooked fiber

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Page 9: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

Graphic 2.4 – Energy absorbed by the fiber.

Finally, dosage, which is the effective quantity of fibers embedded in the concrete (kg/m3

or%Vf 5), certainly impacts considerably on the ductility and toughness levels acquired by the

fiber-reinforced concrete (Graphic 2.6), together with the already mentioned geometric and

mechanical characteristics of the fibers.

It is interesting to observe that through an increase of the aspect ratio (L/D), the quantity of

fibers (dosage) necessary to achieve a given result decreases within certain limits (Graphic 2.5).

This is due to the fact that, statistically, the tensile strength is increased as a direct consequence

of the statistic increase of the fiber length to be pulled-out.

(5) %Vf = Fibers percentual in volume.

Fiber pull-out

Energy absorbed

Fiber breakage

Energy absorbed

DisplacementDisplacementPu

ll-out

load

Pull-o

utloa

d

To fiber pull-out caused bysufficient teensile strength.

To fiber breakage caused byinsufficient teensile strength.

Graphic 2.5 – Dosage vs L/D for the same effectiveness.

Dosa

gefib

er(kg

/m)3

= 33/2x/4x(D/L)2xfs3x7850

100908070605040302010

015 20 25 30 35 40 45 50 55 60 65 70 75 80

Aspect radio (L/D)

fs = 1.00fs = 1.15fs = 1.25fs = 1.35

McKee law

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Page 10: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

It is important to point out that it is definitely the whole set of reported characteristics which

collectively contribute to determine the behaviour of the fiber-reinforced concrete, and that an

optimal output is always depending from an adequate combination of all these factors together

since each factor alone is capable to impact on the final behaviour up to a certain limit, after

which its influence would become useless if not even damaging, as it is highlighted by Graphic

2.6 as far as the influence of dosage is concerned.

The initial part of the curve shows how a very small dosage has practically no effect (degrading

behaviour) because, if only few fibers are dispersed into the mixture, their relative distance is

as high that no resistance is produced.

The second part shows how, by increasing the number of fibers, which is reducing the volume

of influence of each fiber, configurations of static superimposition of fibers between themselves,

with high possibility to interact, are achieved (plastic behaviour). As such, an increase in the

concrete’s ductility is produced, which is directly depending on the effective dosage.

Finally, the third part shows how, by overcoming a certain dosage (hardening behaviour), the

increase in ductility is insignificant, although evident. Thereby, it becomes in contrast increasingly

difficult to obtain a uniform and fluid mixture.

To conclude, the following quantitative considerations can be given regarding the quality and

quantity of fibers to be embedded into a SFRC:

- Fibers should have very high mechanical properties, whereby their tensile strength should be

in the order of 1100 MPa.

- Their aspect ratio should be sufficiently high as well, ranging between 45 and 70.

- Dosage should not be lower than 25 kg/m3, whereby it could reach 40 or 80 kg/m3 for particularly

demanding applications.

Graphic 2.6 – Ductility vs dosage.

Ducti

lity in

creme

nt

Inicial part Second part Third part

Dosage (kg/m3)

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Page 11: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

2.3 - Fiber types – Classification of current commercial fibers in function of the raw material. Organic fibers (natural and synthetic polymers) and inorganic fibers (metallic).

Different types of fibers can be used for concrete, depending from the raw material from which

they are produced:

Metallic: carbon steels and nonalloy steels, aluminium

Natural: asbestos, cellulose, carbon

Synthetic: nylon, polypropylene, polyacronytrile, polyvinylalcohol

A general classification of fibers has been provided by BISFA(6).

Table 2.1 - Mechanical characteristics of the fibers.

Fiber Diâmeter( m)

Density(10 kg/m )3 3

Young´s modulus(kN/mm )2

Tensile strength(kN/mm )2

Elongation at break(%)

Steel

Glass

Asbestos

Polypropylene

Polyethilene

Carbon

Nylon

Kevlar

Acrílic

5 - 500 7.84 200 0.5 - 2 0.5 - 3.5

9 - 15 2.60 70 - 80 2-4 2 - 3.5

0.02 - 0.04 3.00 180 3.30 2 - 3

20 - 200 0.90 5 - 7 0.5 - 0.75 8

- 1.10 4 0.90 13 - 15

- 0.95 0.30 0.0007 10

9 1.90 230 2.60 1

10 1.45 65 - 133 3.60 2.1 - 4

18 1.18 14 - 19.5 0.4 - 1 3

Table 2.2 - Fibers classification by BISFA.

Fibers

Natural Man-made

Organic

CAALGCTA

AcrylicAramidaFiber to chlorineFiber to fluorinePoliamidaPolystyrenePolyethylenePoliamidaPolypropyleneVinylOthers

PANARCLFPTFEPAPESPEPIPPPVAL

CFCEFGFMTF

The polyethylene and polypropylene are polyolefinsThe same code is used in the plastic industry for polyether sulfone (ISO 1043)

By transformation ofnatural polymers

From synthetic polymers:

Inorganic

(6) BISFA = THE INTERNATIONAL BUREAU FOR THE STANDARDISATION OF MAN-MADE FiberS.

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Page 12: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

Note: the present classification concerns all synthetic fibers and not alone fibers used for

concrete.

Some types of fibers:

Loos steel macrofibers. Gludes steel macrofibers. Polypropylene fibers.

Glass fibers. Cellulose fibers. Melt extract steel macrofibers.

Sheet steel macrofibers. Steel microfibers. Macrofibers of high tenacity polypropylene.

Polypropylene microfibers. Synthetic macrofibers. Steel fibers.

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Page 13: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

2.4 - Steel fibers. Classification upon geometrical, physical, chemical, mechanical characteristics and production process.

Fibers are a steel product geometrically characterised by one dimension prevailing onto the

others. Fibers may have a smooth or a worked out surface, they may be employed as reinforce-

ment into a cement conglomerate, they may have straight or shaped configuration, capable to

be homogeneously dispersed into a mixture by keeping unaltered geometrical characteristics

(UNI 11037).

A fiber is geometrically characterised by the length L, the shape and the equivalent diameter De.

The ratio between the length L and the equivalent diameter De provides the aspect ratio, or

shape ratio (l=L/De).

Figure 2.1 - Steel fibers with hooked ends.

Figure 2.2 - Different forms of steel fibers.

Length (L)

Diameter (D)

A fiber can be defined as straight if its longitudinal axis presents localised deformations having

a size which is smaller than L/30, and in any case not greater than its equivalent diameter.

Length L (mm): it is the distance between the two ends of the fiber measured as geometrical

projection with respect to the dominant axis.

Axially, the shape may be straight or shaped; transversely, the fiber may have round, rectangular

or irregular cross-section (Figure 2.2 and 2.3).

De

De De

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Page 14: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

STRAIGHT HOOKED CRIMPED DOUBLEDUOFOR

ORDINARYDUOFORM

PADDLED ENLARGED ENDS IRREGULAR INDENTED

ROUND (wire) RECTANGULAR (sheet) IRREGULAR (mel extract)

(b) Types of cross sections (c) Sticked steel fibers

(a) Various shapes of steel fibers

Figure 2.3 - Different forms of steel fibers.

Equivalent diameter De (mm): it is defined by means of different methods, depending from the

cross-sectional shape and the production process.

Direct method

In the case of fibers obtained from wire, disregarding from the longitudinal shape, the equivalent

diameter De is equal to the nominal diameter of the original wire or of the finished fiber.

Indirect geometric method

In the case of fibers obtained from laminate, disregarding from the longitudinal shape, the

equivalent diameter De is equal to the circle having the same area as the fiber cross-section

given by the following relation.

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Page 15: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

Whereby A is the area of the fiber cross-section (mm2).

Where w = width, t = thickness

Indirect gravimetric method

In the case of fibers manufactured using other production methods and having a variable cross-

section, disregarding from the longitudinal shape, the equivalent diameter is calculated based

upon the mean length L of the fibers, the mean weight m [g] of a given number of fibers, and

on the base of a volumetric mass r = 7.85 g/cm3, following the relation:

Simplifying, in the case of steel fibers:

Following prEN 14889-1. Fibers for concrete. Part. 1: Steel fibers, the equivalent diameter is

calculated from the fully developed length of the fiber Ld obtained by flattening or straightening

the fiber by hand or by hammering.

Number of fibers per kilogram [n°/kg]

The number of fibers in a kilogram is calculated using the following relationship:

where:

L = Length of the fiber (mm)

De = Equivalent diameter of the fiber (mm)

g = Density (kg/m3)

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Page 16: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

The aspect ratio [l=L/De] defines the slenderness of the fiber: for the same fiber length, the higher

is the aspect ratio, the smaller is the equivalent diameter, which is the thinner is the fiber.

Moreover, for the same fiber length, the greater the value of l, the more lightweight the fiber

is, indicating a higher fiber density.

If the direct method and the indirect geometric method are applied, the aspect ratio neglects

the longitudinal shape, thus the volume and weight of the fiber.

If, in contrast, the indirect gravimetric method is applied, the aspect ratio takes the effective

geometry of the fiber into account through the fiber’s mass:

The tensile strength Rm [N/mm2 or MPa] of the fiber is calculated by dividing the tensile force

necessary to break through the cross-section of the fiber or of the intermediate product (UNI EN

10218 for wire). Besides the tensile strength Rm, the standard UNI 11037 foresees that the tensile

strength for a residual deformation set of 0,2 %, Rp0,2

, is indicated as well. Again, in the same Ital-

ian standard, the tensile strength is divided into three classes, R1, R2 and R3. Each of these three

classes is further subdivided depending upon the case that the tensile strength is referred to the

intermediate product applied to obtain straight fibers:

1) Straight fiber: in this case is does not matter to test the intermediate product or the fiber itself,

and the case that the tensile strength is referred to the intermediate product applied to obtain

shaped fibers.

2) Fiber with hooked ends: In that case, and for a same class, the strength threshold is higher if it

is foreseen that the shaping / forming process produces a detriment of the tensile strength of the

fiber. This classification of tensile strength takes into account the diameter of the fiber: to decreas-

ing diameters correspond increasing strength thresholds.

Table 2.3 - Tensile strength for three fibers classes according to Italian norm.

Equivalentdiameter

(mm)

Tensile strength(N/mm )2

R 11) 2)

Rm400350300

Rp0.2320280240

Rm480450390

Rp0.2400350300

R 21) 2)

Rm900800700

Rp0.2720640560

Rm1.0801.040910

Rp0.2900800700

R 31) 2)

Rm1.7001.5501.400

Rp0.21.3601.2401.120

Rm2.0402.0151.820

Rp0.21.7001.5501.400

Tensilestrengthtest

All theclass

Tensilestrength

NOTE: The indicated mechanical properties in the present table mention all to it the types of steel fib re s.1) Straight fib re s.2) Profiled fib re s.

0.15 D < 0.500.50 D < 0.800.80 D < 1.20

<<<

e

e

e

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Page 17: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

In prEN 14889-1. Fibers for concrete. Part. 1: Steel fibers the category “Other production

methods” is further detailed:

Group I: cold-drawn wire;

Group II: cut sheet;

Group Ill: melt extracted;

Group IV: shaved cold drawn wire;

Group V: milled from blocks.

Chemical composition

The raw material might have various chemical compositions. It is for this reason that in the

standard UNI 11037 a prospect for the chemical analysis of casting has been elaborated.

Table 2.4 - Fibers classification in function of its chemical composition.

Ductility

To evaluate the ductility of a fiber, or of the intermediate product from which it is obtained, alternate

bending tests are applied. If drawn wire has to be considered, please refer to UNI EN 10218.

Production process

Following the standard UNI 11037, according to the production process different types of fibers

can be considered:

- Cold-drawn steel wire obtained from rod produced following standard UNI EN 10016-

1,2,4 or UNI EN 10088-3

- Cold-laminated sheet of non-alloy (plain carbon) steel

- Other production methods (such as, e.g., milling from a steel block)

The classification of fibers is further cross-impacted by the chemical composition:

Surface coating

In order to guarantee durability in the case that the fibers are applied in particularly aggressive

environments, fibers may have a zinc surface coating. The following table presents coating thick-

ness as a function of wire diameter:

Table 2.5 - Chemical composition of steel fibers according to Italian norm.

AFibers from drawn wire

A1Low Ccontent

A2High Ccontent

A3Inox

BFibers from cut laminated sheet

B1Low Ccontent

B2High Ccontent

B3Inox

COther production methods

C1Low Ccontent

C2High Ccontent

C3Inox

Type of steel

A1-B1-C1A2-B2-C2A3-B3-C3

<<

0.200.20

1)

1)

C<<

0.600.80

2)

2)

Mn<<

0.300.30

Si0.0450.06

0.0450.05

Smax. Pmax. Cr----

Ni----

Following UNI EN 10088-1

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2. Fibers as structural element for the reinforcement of concrete.

Tolerances

Standards (UNI 11037, prEN 14889-1 and ASTM A820) provide different criteria for the evaluation of toler-

ances. The following table reports the most restrictive conditions provided by prEN 14889-1, which prescribes

that the percentage of conformity should not be less than 95 % of the verified specimens (whereby ASTM

A820 considers 90%, and additionally, with deviation onto the higher average nominal values):

Table 2.6 - Minimum zinc coating for steel fibers.

Table 2.7 - Dimensional tolerances of steel fibers according to European norm.

The least 95% of the individual samples the specified tolerances must be in agreement.

Table 2.8 - Dimensional tolerances of steel fibers according to American norm.

The least 90% of the individual samples the specified tolerances must be in agreement.

Standard prEN 14889-1 indicates tolerances for the tensile strength and the Young’s modulus.

For tensile strength, a tolerance of 15% is considered onto the average value, and a tolerance of

7.5 % is considered onto individual values; at least the 95% of the specimens must be conform

to the above indicated tolerances.

Diameter (mm) Minimum coating mass (g/m )2

0.15 D < 0.50

0.50 D < 0.80

0.8 D < 1.20

<

<

<

e

e

e

15

20

25

prEn 14889-1 - Tolerances

Property

Length> 30 mm

30 mm<Equivalent diameter

> 30 mm30 mm<

Length/diameterratio

Symbol

L

De

= L/De

Deviation of the individual valuerelative to the declared value

+ 10% ++

5%1.5 mm

++

5%0.015 mm+ 10%

+ 15% + 7.5%

Deviation of the average valuerelative to the declared value

ASTM A820 - Tolerances

Length

Equivalent diameter

L

De

= L/De

+ 10% + 10%

+ 10%

+ 15%

+ 10%

+ 15%

Property Symbol Deviation of the individual valuerelative to the declared value

Deviation of the average valuerelative to the declared value

Length/diameterratio

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Page 19: Manual beton armat cu fibre

2. Fibers as structural element for the reinforcement of concrete.

2.5 - Synthetic and natural fibers. Classification based upon geometric, physical, chemical, mechanical characteristics and production process.

Synthetic fibers for use in the most common concretes can be grouped as indicated by the

following figure, taken from a BISFA document:

Designation

Following UNI 11037/2003 “steel fibers to be employed in the manufacture of fiber-reinforced

cement conglomerate”, fibers are designated through the following short-name:

UNI 11037 – A1 – 1.00 x 50 – R2 – shaped

Where:

A = indicates fibers obtained from drawn wire

1 = indicates low carbon content

1.00 = indicates the fiber diameter

50 = indicates the fiber length measured between its ends

R2 = indicates the 2nd tensile strength class (R > 910 MPa for the considered diameter)

Shaped = indicates transverse or longitudinal deformations greater than L/30

Fiber composed of linear macromoleculesmade up of saturated aliphatic hydrocarbonunits in which one carbon atom in twocarries a methyl side group, generally in anisotactic configuration and without furthersubstitution.

Polypropylene Polyproyilene

Linear macromolecules of poly (vinylalcohol) whith different levels ofacetalization.

Vinylal Acetalized poly (vinyl alcohol)

Where n > 0

Fiber composed of linear macromleculeshaving in the chain at least 50% and lessthan 85% by mass of acrylonitrile.

Modarcrylic Acrylic copolymers

If X = H e Y = ClPoly(acrylonitrile or vinyl chloride)

If X = Y = ClPoly(acrylonitrile or vinylidene chloride)

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2. Fibers as structural element for the reinforcement of concrete.

2.6 - Current standard situation.

From raw material to the intermediate product, the following standards can be applied (in a

European contest):

- UNI 5549 Mechanical tests for metallic materials – Alternate bending tests of thin

steel sheets and tapes with thickness below 3 mm.

- UNI EN 10002-1 Metallic materials – Tensile test – Part 1: Test method (at ambient

temperature).

- UNI EN 10016 Rod of non-alloy (plain carbon) steel destined to cold-drawing and/or

to cold-lamination.

- UNI EN 100 Stainless steels.

- UNI EN 10130 Flat cold-laminated products made of low carbon content steel for

dishing or cold bending.

- UNI EN 10204 Metallic products – Types of control documents.

- UNI EN 10218-1 Steel wire and wire products - Part 1: Generalities – Test methods.

- EN 10244-2 Steel wire and wire products – Non-ferrous metallic coatings on steel

wire – Part. 2: Zinc or zinc alloy coatings on steel wire.

- ECISS CR 10261 Information circular n. 11 – Steels and cast irons – List of available

chemical analysis methods.

Table 2.9 - Classification of synthetic fibers according to BISFA.

Fiber composed of linear macromoleculeshaving in the chain recurring amide linkages,at least 85% of which are joined to aliphaticcycloaliphatic units.

Polyamideornylon

Polyhexamethylene adipamide (polyamide 66)

Fiber composed of linear macromoleculesmade up of aromatic groupps joined byamide or imide linkages, at least 85% ofthe amide or imide linkages being joineddirectly to two aromatic rings and thenumber of imide linkage, if the latter arepresent, not exceeding the number ofaramide linkages.

Aramid Example 1:

Example 2:

Note: In example 1. the aromatic groups may be thesame or different.

Polycaproamide (polyamide 6)

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2. Fibers as structural element for the reinforcement of concrete.

Specific standards concerning steel fibers are:

- UNI 11037 Steel fibers to be applied for confection of fiber-reinforced cement con-

glomerate.

- ASTM A820 Standard specification for steel fibers for fiber-reinforced concrete.

- prEN 14889-1 Fibers for concrete – Part 1: Steel fibers – Definition, specifications and

conformity.

The standard EN 14889-1 has been further elaborated by CEN/TC104/WG11, under Man-

date M128, CPD 89/106, and has been approved by the Formal Voting of May 2006. This is

a harmonized standard. The following scheme depicts the standard and the other correlated

standards:

Table 2.10 - Outline of the Norms prEN 14889-1 and correlated.

CEN Enquiry(July 2003)

CEN Enquiry( 2004)May

Construction ProductDirective

CPD 89/106

M128Products related toConcrete, Mortar

and Grout

CEN/TC104/WG11Concrete

fibers for concret

CEN/TC229/WG3/TG7Precast concret products

Test method for metalic fiber

prEN 14845-2Test method for fibers

in concretPart 2 - Effect on strenght

prEN 14651Test method for metalic

fiber concretMeasuring the flexural

strenght

prEN 14845-1Test method for fibers

in concretPart 1 - References

concret

CEN Enquiry(May 2004) CEN Enquiry (August 2004)

prEN 14889-1Fibers for concretPart 2. Steel fibers

prEN 14889-2Fibers for concret

Part 1. Polymer fibers

CEN Enquiry (August 2004)

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2. Fibers as structural element for the reinforcement of concrete.

2.7 - List of MACCAFERRI’s fibers. Classification of MACCAFERRI’s fibers.

Officine Maccaferri produces shaped fibers and fibers cut from cold-drawn steel wire. Chemical

characteristics of the raw material (rod) are reported in the following table, in function of the

final diameter of the fiber:

Table 2.12 - Qualitative behavior of the Maccaferri fibers.

Code ofthe Fiber

Fiber classificationaccording to

productive processMaterial ofproduction

Dimensions

Length(mm) (mm)

DiameterAspectratio(L/d)

Number offibers for kg(n°/kg)

Inorganic 33 0.75 44 8651

Inorganic 33 0.60 55 13518

Inorganic 33 0.55 60 16087

InorganicMultifilament of

virgin polypropylene 12 0.02 180.000.000(for ofmixture)

m3

Vegetalorganic

Multifilamento ofvirgin cellulose 02:01 0.02 1.450.000.000

Inorganic Meltextracto

Tensilestrength

(MPa)

Wirand FF1 InorganicCold-drawn wire

with lowcarbon content.

Cold-drawn wirewith low

carbon content.

Cold-drawn wirewith low

carbon content.

Cold-drawn wirewith low

carbon content.

Cold-drawn wirewith low

carbon content.

Cold-drawn wirewith low

carbon content.

50 1.00 50 32121100

Inorganic 50 0.75 67 57101200

Inorganic 37 0.55 67 143481200

1200

1200

1300

320-400

90-130 ksi

800 32 0.4 765732

Wirand FF3

Wirand FS1

Wirand FS3N

Wirand FS4N

Wirand FS7

FibroMac 12

Ultrafiber 500

MC1

WirandFF1

Maximum performance

Qualitative properties of thesteel fiber reinforced concrete.

Ductility and tenacityFatigue resistanceImpact resistance

PermeabilityMicrocracking controlAbrasion ResistanceLong term shrinkage

Fire resistance

WirandFF3

WirandFS1

WirandFS3N

WirandFS4N

WirandFS7

MC1FibroMac12

Ultrafiber500

Minimum performance

Table 2.11 - Maccaferri fibers.

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2. Fibers as structural element for the reinforcement of concrete.

Table 2.13 - Application guide of the concrete fibers reinforced. Orientation according to type of fiber and thicknesses.

Maximum diameter of aggregates (mm) 25 25 18 15 15 15 25 Advisedaddition

Advisedaddition

Prefa

brica

tedan

d othe

rs

Light

Pretensile

Extruded

Channel linings

25

35

20

40

200

300

100

250

25

30

20

35

200

300

100

250

20

30

60

250

25 50 20

35

50

250

20

35

50

250 35

40

30

300

20 150 20 150 30 200

300

200

0.6 / 0.10

1.9

0.6 / 0.10 0.6 / 0.9

0.6 / 0.90.6 / 0.9

300300

3560

150150 25150 30150 3525

30 30060 350 50 350

50 3060 3025 50 25 50

50 50 50 50

0.6 / 0.10

0.6 / 0.10

30 150 25 150

25 150 20 150

Minimum dosages andminimum thicknesses (mm)

(kg/m³)Wirand

FF1Wirand

FF3Wirand

FS1WirandFS3N

WirandFS4N

WirandFS7 FibroMac

12Ultrafiber

500

MC1Wirand

FF1(mix)

Dos. Dos.Thick. Dos. Dos. Dos. Dosage

Industries

Airports

Commercial areasImprovement of sub-basefoundationFoundation for machines baseFlo

orsa

ndpa

veme

nts

Primary linings

Final liningsPrecast segmentTu

nnels

35 300

Thick. Thick. Thick. Thick. Dos. Thick. Dos. Thick. Dosage

Comments:

All the advised dosages and thicknesses in this table are based on experiences, therefore they can vary each in accordance with case that will have particu-

larly to be studied.

To consult the Structural Engineering department of the Maccaferri for a correct orientation to its project.

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3. Fiber reinforced concrete; Basic elements for the structural project.

Introduction

By adding to concrete fibers of different kinds, either micro or macro fibers, as related in the previous chapter, a new material with features different from normal concrete is obtained.

Such a mixture is called Fiber Reinforced Concrete. If it’s a reinforcement made of steel fibers it’s called Steel Fiber Reinforced Concrete.

The surveys of FRC different technological properties are made by normalized tests, some of which typical of ordinary concrete, some others made on purpose for the fiber reinforced one.

Properties of the fiber reinforced concrete in hardened state

Here are the factors which affect the properties of a fiber reinforced concrete:

- The fibers: geometry, aspect ratio, contents, orientation and distribution; - The matrix: resistance and maximum dimension of the aggregates; - The interface fiber-matrix; - The tests: test dimensions, geometry and methodology.

The properties of under load (static and dynamic) fiber reinforced concrete may be classified accord-ing to the following actions:

- Compression; - Uniaxial direct traction; - Splitting indirect traction; - Bending indirect traction (measure of toughness and fracture energy); - Shearing and torsion; - Fatigue; - Impact; - Abrasion; - Viscous deformation (Creep).

The physical and chemical behaviour is to be valued according to the following phenomena:

- Short-term shrinkage (plastic); - Long-term shrinkage (hydraulic); - Durability; - Freeze-thaw; - Carbonation;

3.1 - Mechanical characterization of fiber reinforced concrete. Most important resistant features.

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3. Fiber reinforced concrete; Basic elements for the structural project.

- Fibers corrosion in the presence of chlorides (cls cracked and not cracked); - Exposure to the fire.

For each of the above-mentioned features suitable prescriptive references will be given.

Compression

Concrete compressive strength isn’t substantially modified by fibers addition.

A moderate increase for considerable rates of steel fibers (no less than 1.5% in volume, approxi-mately) can be observed.

After reaching the peak, the material shows a marked ductility which strongly depends on fibers contents:

Again about the behaviour of fiber reinforced to compression, the elastic modulus and the ratio of Poisson prove to be substantially unchanged for rates of fibers lower than 2% in volume.

Strength tests are made on cylindrical (diam 150mm, height 300mm) or cubical (side 100 or 150mm) specimen. Reference prescriptions are the same applied to ordinary concrete (ASTM C39, EN 12390-3, etc.).

Uniaxial direct traction

Fiber reinforced behaviour to uniaxial traction is strongly affected by the presence of fibers, particu-larly in the phase following the first cracking.

Graphic 3.1 - Chart load vs. deformation, for concrete with different fiber dosages.

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3. Fiber reinforced concrete; Basic elements for the structural project.

Only by using high measurings, above all of microfibers (about 1.5 – 2% in volume and above), re-markable additions of peak value can be obtained:

It’s the case of High Performance Fiber Reinforced Cement Composites (fck > 100 MPa) and with

high short fibers measurings (Lf < 13 mm, measuring > 2% volume), where the behaviour turns into

hardening kind.

The direct traction test of fiber reinforced concrete isn’t easy to be carried out.

As it may be proved by the following picture, it’s better to engrave the specimen so as to spot the crack:

Graphic 3.2 - Load curve (P) vs. deformation (δ), for concrete with low fiber dosage (a) and high fiber dosage (b).

Figure 3.1 - Arrangement for direct tensile strength test.

Figure 3.2 - Arrangement for fiber reinforced concrete tensile strength test according UNI U73041440.

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3. Fiber reinforced concrete; Basic elements for the structural project.

At present there are no regulations on direct traction.

The UNI U73041440 norm, which provides some information on dimensions of the specimen, cy-lindrical or prismatical, on the engraving depth, by which the cracking aperture can be measured, is being passed in Italy.

Indirect traction – Brazilian test

The practical difficulties to carry out the direct traction led to alternative procedures, as the splitting indirect traction, also called “Brazilian test”:

In the picture the specimen is cylindrical but it’s also possible to test cubical or prismatical speci-men.

The test consists in subjecting a cylindrical specimen to a compression force applied to a restricted zone for the cylinder overall length.

The breaking comes after reaching the maximum traction strength in direction orthogonal to the applied force. The fiber reinforced concrete indirect traction strength is obtained by the maximum load.

To determine such a property it’s possible to apply to ASTM C496 and EN 12390-6 norms.

As for ordinary concretes, it’s possible to deduce the direct traction strength following up the in-direct one (EC 2, Italian Technical Norms, ACI). The possible correlations also for fiber reinforced concretes aren’t at present codified.

Indirect traction - Bending

The bending test is surely the most widespread owing to its carrying out relative facility and as it is representative of many practical situations. Another reason for the success of this test comes from the higher degree of the test redundancy, which points out the ductility brought by the fibrous rein-forcement, more than it happens in the previous tests (compression and direct traction):

Figure 3.3 - Arrangement for Brasilian concrete tensile strength test.

Photo 3.1 - Indirect tensile strength test apparatus.

Photo 3.2 - Example of configuration for indirect tensile strength test element.

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3. Fiber reinforced concrete; Basic elements for the structural project.

There are two kinds of tests: bending test on prismatical specimen (beam) and plate (circular or square) punching test.

Bending test on beam:

This test aims at determining the toughness brought by the fibers to concrete.

The toughness is the strength opposed by the material to the feed of breaking process (static, dy-namic or after shock) owing to its capacity of dispersing energy distortion.

The specimen rests on two points, and is loaded in one or two points: the former case is called Three Point Bending Test (3PBT), the latter Four Point Bending Test (4PBT) (Figures 3.4 and 3.5):

Graphic 3.3 - Results comparison of fiber reinforced concrete tensile strength with different dosage rates.

0.00 0.10 0.20Displacement w (mm)

5.0

4.0

3.0

2.0

1.0

0.0

Aver

age

tens

ion

(MPa

) t

TRA0 medTRA4 medTRA8 med

zoom w = 0.2 mm

Graphic 3.4 - Results comparison of fiber reinforced concrete flexural strength with different disage rates.

FLE0 medFLE4 medFLE8 med

zoom w = 5.00 mm12.0

8.0

4.0

0.00.00 2.50 5.00

Deflection f (mm)

Load

P(k

N)

Plain

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3. Fiber reinforced concrete; Basic elements for the structural project.

The beam on three load points is loaded at midspan, while in the four points one the span is divided in three parts of equal length.

The beams dimensions in the main regulations aren’t so different one from another.

In ASTM C1018 norm, according to the fibers length, it’s possible to choose between two different structures:

Support Loading device

Support

L

Figure 3.5 - Configuration of flexural test with the four point load arrangement.

Figure 3.4 - Configuration of flexural test with the third point load arrangement.

Standard Specimen andloading

Specimendimensions

Parametersmonitored Measurements

- Beam- Third-point loading

100 x 100 x 350 mmpreferred(variations permitted)

- Load- Net deflection atmidspan

- First crack strength and deflection- Toughness index 15, 110, 120 (ratio of energyabsorbed up to n and that absorbed energy up to

- Residual strength factor(s)

r

r

(n = 3; 5,5; 10,5)

- Beam- Third-point loading

d/b < 1,5l = 3ds > 3d + 50 mm

- Load- Deflection at midspan

- Load- Net deflection atmidspan

- First crack strength- Energy absorbed until the deflection of 1/150Ratio of energy absorbed up to deflection of15,5 to that up to-

r r

b = d = 140 mml = 420 mms = 560 mm

- Load- Deflection at midspan(avg)

- First crack load P- Ratio of load at deflection to load P( = 0,7; 1,4; 2,8 mm)

r

r

- Beam- Third-point loading

b = d = 150 mml = 3d4d s 5d< <

- First crack strength- Flexural strength- Energy absorbed up to deflection l/n (n = 300, 150)- Equivalent flexural strength up to deflection l/n(n = 300, 150)- Ratio of load at a deflection of l/n (n = 300, 150) tothe first crack load

- Beam- Third-point loading

- Beam- Third-point loading

h = d = 100 mm forl < 40 mmh = d = 140 mm forIf > 40mml = 3d + 80 mm

l

- Load- Net deflection atmidspan, or Netdeflection at loadpoints

- Flexural strength- Load ratio P* / P (P* = maximum loadon reloading after unloading at 0,9 P in thepost-peak; P = maximum load)

max max max

max

max

h = d = 150 mml = 600 mms = 700 mm

- Total load- Net deflection atmidspan (avg)

- First crack strength- First crack load- Equivalent flexural load carrying capacity untildeflection- Equivalent flexural strength until deflection

G fiberslimit = ( / )limit

h = d = 150 mml = 450 mms = 600 mm

- Total load- Net deflection atmidspan

- First crack strength and load- Energy absorbed up to deflection ( = 1,5, 3 mm)- Equivalent flexural strength up to deflection to thefirst crack strength

ASTM 1018-92

UNE 83-510-89Spain

P 18-409France

NBN B 15-238Belgium

ConcreteInstituteJSCE-SF4Japan

DBV Recommendat(Germany)

CUR Recommend(The Netherlands)

ConcreteAssociationRecommendNorway

h = 125 mmd = 75 mml = 450 mms = 550 mm

- Total load- Load point deflection

- Flexural strength- Residual flexural strength at deflections of 1 mmand 3 mm- Toughness classification based on residual flexuralstrength

- Beam- Third-point loading

- Beam- Third-point loading

- Beam- Third-point loading

Table 3.1 - Comparison table of different international codes, description and results.

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3. Fiber reinforced concrete; Basic elements for the structural project.

The bending test may be represented by a Load curve – Vertical displacement (measured under load points) or, if the specimen is engraved, by a Load curve – Crack Opening Displacement or COD), so as it can be seen in the following picture:

Graphic 3.5 - Example of UNI 11039 flexural test. Load vs. crack opening.

Stiffnessratio(mm )2

Nº Country Standard Issued Dimensions/spanw x d x l/s (mm)

System/loading

Flex.strength

Cq. flex.strength

Res. flex.strength

Tensilestrength Specialties

781,3nn World RilemTC 162-TDF 2000

150 x 150 x 550 / 550(150 x 125 x 550 / 500)

3 pt/centrally

LOP (Fu)0,05 mminterval

l/1000(0.5 mm)l/200

(2.5 mm)- 0.37 x flex.

0.45 x flex

0.37 x flex.0.45 x flex

Notched beamsConcrete partof absorptiontaken intoaccount

370,41 Suisse SIA 162/6 1999h0 x h0 x 6h0 / 4,5h0

(h0 100) 4pt/3 ptrd - Dependent oncrack location - - Crack location

normalized

260,42 NorwayNBpublicationn°7

1999 125 x 75 x l / 450( l 500) 4 pt/3 ptrd Fu

(1 crack)st -0.5 mm1.0 mm2.0 mm4.0 mm

- -

937,53 Germany DBVtunneling 1996 150 x 150 x 700 / 600 4 pt/3 ptrd

Fu(1 crack)0,05 mminterval

stl/1200

(0.5 mm)l/200

(3.0 mm)

-Concrete partof absorptiontaken intoaccount

0.37 x flex.260,4723,44 Sweden SB Report

nr 4 1997125 x 75 (125) x l / 450

(l 550)Fu, Fcr(specialmethod)

- fcr x R10, x/100(ASTM 1018)

Refers toDBV, ASTM

-1250,05 SpainAENOR UNE83-5xxCIMNE n°54

2000

1989150 x 150 x 600 / 450

4 pt3 pt/

centrally

pt/3rd

Fu, Fcrl/300

(1,5 mm)l/150

(3,0 mm)- -

-1250,06 Netherlands CUR 35Komo-Attest

19941997 150 x 150 x 600 / 450 4 pt/3 ptrd

Fu(1 crack)0,05 mminterval

st

Fu, Fr0,05 mminterval

l/300(1,5 mm)l/150

(3,0 mm)R = feq/fcr -

-555,61250,07 Austria

OBVguidelinefor shotcrete

1998 100 x 100 x 400 / 300150 x 150 x 600 / 450 4 pt/3 ptrd - (DBV)

Toughnessclasses

l/600 l/150-

-1250,08 Belgium NBNB-15-238 1992 150 x 150 x 600 / 450 4 pt/3 ptrd l/300 (1,5 mm)

l/150 (3,0 mm) - -

FuFr (0,05mminterval)

-1088,99 France NF P 18-409 1993 140 x 140 x 560 / 420 - -l/600 (0,7 mm)l/300 (1,4 mm)l/150 (2,8 mm)

ctility factorsdx.x = Fx.x/Fcr

Fu -555,61250,010 Japan JSCE-SF4 1984 100 x 100 x 380 / 300

150 x 150 x 530 / 450 4 pt/3 ptrd

l/600 (0,75 mm)l/300 (1,5 mm)l/200 (2,25 mm)l/150 (3,0 mm)

Residualfactor afterreloadingF 0.9/Fu

Reloadingof specimen

Fcr -555,61250,011 USA

ATSMC 1018 1997 100 x 100 x 350 / 300

150 x 150 x 500 / 450 4 pt/3 ptrdToughnessindicesIxx

Residualstrength

factors Rx,x

Evaluation stagesdepending oncracking

displacement

4 pt/3 ptrd

R60-FF3-35 - Vf=0,45%

0,0

1,0

2,0

3,0

4,0

5,0

6,0

7,0

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5CTODm (mm)

CTODm ACTODm BCTODm CCTODm DCTODm ECTODm FCTODm G

Nom

inalstress

(MPa

)

Table 3.2 - Comparison table of different flexural test international codes, description and results.

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3. Fiber reinforced concrete; Basic elements for the structural project.

The Italian norm UNI 11039 is based on bending tests on 4 points in control of crack aperture.

Figure 3.6 - Example of first crack moment definition. Energy absorption calculation in the post cracking phase in the load vs. crack opening chart.

A particularly interesting parameter is the “first crack point”, starting from which the fibers start to give their share.

This parameter is prearranged, owing to the difficulty to determine the trigger of crack procedure.

The first crack formation is associated by some regulations to the loss of linearity of the load-dis-placement curve (ASTM), while in further cases it is associated to the intersection between the load-displacement curve and a parallel to the linear outline starting from a uniform value of 0.05 mm on abscissae axis (vertical displacement) (RILEM, CUR, DBV, AFNOR, NBN).

As for the behaviour in postcracking phase, the regulations are based on the definition of dimen-sionless ductility indexes based on the energy dispersed in the cracking procedure and/or on the residual strength.

In ASTM C1018 norm it’s calculated the area subtended by the Load-Displacement curve for mul-tiple values of the first crack displacement; in other cases it’s assumed the punctual residual strength for a vertical displacement denominated as ratio of the beam span (NBN, JCI-SF4).

The recent European norm EN 14651 locates the postcracking residual strength values as punctual values of crack aperture: the RILEM norm assumes “equivalent” strength values which are obtained by the energy absorbed in crack aperture intervals

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3. Fiber reinforced concrete; Basic elements for the structural project.

The UNI 11039 norm allows to classify the fiber reinforced concrete according to its resistance and its toughness.

The first crack strength (fIf) derives from the relation

Where: - l is the distance between inferior supports (450 mm) - b is the width of the beam (150 mm) - h is the height of the beam (150 mm) - a

0 is the depth of the engraving (45 mm)

The norm provides as well the determination of two post-crack strengths: the former, typical for exercise

Photo 3.3 - Frontal view of an instrumented specimen before the beginning of the test.

Figure 3.7a - Geometry and restraints for fiber reinforced concrete beams. Figure 3.7b - Detail of the triangular shaped engraving.

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3. Fiber reinforced concrete; Basic elements for the structural project.

With:

The UNI 11039 norm (2003) proposes to determine two “Ductility indexes” defined as:

Bending test on plate

The bending test on plate, also called punching test, was codified for the first time by SNCF (French Railways Company) in 1989.

Unlike the bending test on beam, in this case a plate, square or circular, is subjected to central concentrated load, so as to determine, for a prearranged lowering of the load point, the absorbed energy.

Both in case of square plate and in case of circular plate, the lowering is equivalent to 1/20 of the free span, so as to generate a very large cracking sight, concerning more than a cracking line of remarkable width.

Graphic 3.6 - Typical Load – CTOD curve. Graphic 3.7 - Crack intervals considered for the calculation of equivalent tensions.

U1 U2

P If

Load

CTOD0 CTOD + 0.6mm0 CTOD + 0.3mm0

U1 U2

Stre

ss

mm0.3 0.6 1.8 3

.. . .

. .

. . .

.

conditions, is the medium tension in the stretch with crack aperture at the top of the engraving (CTOD) variable between 0 and 0.6 mm (f

eq (0-0.6)

); the latter, typical of breakdown conditions, is the medium tension in the stretch of crack aperture variable between 0.6 and 3.0 mm (f

eq(0.6-3.0)):

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3. Fiber reinforced concrete; Basic elements for the structural project.

This kind of test has become very popular in common in usual practice being fairly easy to be carried out. On the other hand, the results show a marked statistical dispersion, owing to the redundant bond: that’s why it’s spreading, starting from the USA, the test on circular plate put on 3 spherical hinges and for this reason statistically determined.

Figure 3.8 - UNI 10834 or EFNARC test arrangement. Plate test or energy absorption test.

Photo 3.4 - UNI 10834 or EFNARC test full configured front view.

Photo 3.5 - Example of ASTM C1550 energy absorption test configuration.

Figure 3.9 - ASTM C1550 plate test, geometric arrangement.

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3. Fiber reinforced concrete; Basic elements for the structural project.

A schedule of the existing regulations is following.

Shearing and torsion

Generally, steel fibers increase the strength to shearing and to concrete torsion.

After test carried out on beams in which fibers for shearing and longitudinal framework for bending had been used, it’s possible to state that fibers can replace partially or totally the traditional hangers for tangential strains, by modifying the mechanism of shearing cracking in bending cracking, with suitable contents and kind of fiber.

A few formulations of beams shearing strength (ACI Building Code, Walraven, etc.) have been sug-gested.

Some of them are following:

(ACI Building Code)

(Walraven)

(ACI Building Code – simplified rel.)

Nº Country Standard Issued Dimensionsa x b x d/s (mm) System/loading Toughness classes Specialties

nn UE CEN TC229 - 600 x 600 x 100 / 500 E in J -

nn UE EFNARC 1996 600 x 600 x 100 / 500 Allround hinged,centrally loaded

100 x 100

Allround hinged,centrally loaded

100 x 100E1: > 500 JE2: > 700 JE3: > 1000 J

(@ 25 mm defl.)

-

1 Suisse SIA 162/6 1999 600 x 600 x 100 / 500Ø 800 x 100 / 700

Allround hinged,centrally loaded

100 x 100

l: 500 Jll: 800 J

lll: 1000 J(min G = 4 kN/m)

Calculation of equivalentflex. tensile strength

2 NorwayNBPublicationn°7

1999 600 x 600 x 100 / 500Allround hinged,centrally loaded

100 x 100E700: > 700 J

E1000: > 1000 J-

3 AustriaOBVGuideline forShotcrete

1998 600 x 600 x 100 / 500Allround hinged,centrally loaded

100 x 100

E1: > 500 JE2: > 700 JE3: > 1000 J

(@ 25 mm defl.)

-

4 EUA ASTMC1550-05 2005 Ø 800 x 75 / 700 4 pt/3 pt support @ 5, 10, 20, 40 mm Bernard´s statically

determined test

Table 3.3 - Comparison table of different energy absorption test or plate test.

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3. Fiber reinforced concrete; Basic elements for the structural project.

Generally, it’s possible to state that the field of validity of all the expressions above is anyway still rather restricted, as they derive from experimental observations and as specific national regulations don’t exist.

Fatigue

The increase of fatigue strength caused by the introduction of fibers is well known: in support there exists a wide literature based on several experimental campaigns.

The tests dimensions and procedures are various: in this case, too, there are no regulations in this matter.

The fatigue strength can be defined as the maximum stress level to which the fiber reinforced con-crete can resist for a definite number of load cycles before cracking, or as the maximum number of load cycles necessary to breaking for a definite stress level (ACI Committee: Report 544.1R – Fiber Reinforced Concrete; Report 544.2R – Measurement of Properties of Fiber Reinforced Concrete).

Impact

The behaviour of fiber reinforced concrete may be studied by various test procedures (ACI Commit-tee: Report 544.2R – Measurement of Properties of Fiber Reinforced Concrete):

1. Weighted Pendulum Charpy-type impact test; 2. Drop-weight test (single or repeated impact); 3. Constant strain-rate test; 4. Projectile impact test; 5. Split-Hopkinson bar test; 6. Explosive test; 7. Instrumented pendulum impact test;

For instance, in the case 2, the number of drops necessary to generate a certain level of damage in the specimen is measured.

With these kinds of tests it’s possible to compare:

1. Difference of behaviour between fiber reinforced and ordinary concretes; 2. Difference of behaviour between fiber reinforced subjected to impact and static load.

Some experiments carried out by several researchers have proved that, by using drop-weight proce-dure, it’s registered a very strong increase of the strength of normal strength concretes, of about 6-7

(Minelli)

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3. Fiber reinforced concrete; Basic elements for the structural project.

times in comparison with not reinforced concretes, with measurings in volume equivalent to 0.5% of steel fibers.

Abrasion

The calculation of abrasion, cavitation and/or erosion strength may be carried out by ASTM C418 and C779 tests.

Particularly interesting it’s the use of fiber reinforced to prevent or repair the damages caused by cav-itation, as it was experimentally proved in laboratory by carrying out some tests according to ASTM C779 - C779M-05 Standard Test Method for Abrasion Resistance of Horizontal Concrete Surfaces.

Another suggested procedure is CRD-C 63-80 “Test Method for Abrasion-Erosion Resistance of Concrete (Underwater Method)”, U.S. Army Corps of Engineers.

On the other hand, it isn’t easy to prove the advantage brought by fibers in improving the behaviour of the surfaces subjected to traffic of tyred vehicles.

Viscous deformation (Creep)

The tests carried out so far don’t show remarkable differences between ordinary and fiber reinforced concretes (fibers contents < 1%) subjected to compression prolonged in time.

The norm for the test is the same as for ordinary concrete: ASTM C512-02 Standard Test Method for Creep of Concrete in Compression.

Short-term shrinkage (plastic) – Plastic Shrinkage Cracking

The plastic shrinkage cracking develops owing to water leak in the transformation from the liquid to the plastic state.

The concrete plastic shrinkage may be efficiently controlled by using microfibers of polymeric kind in virtue of the very high specific surface of such fibers for volume unit and therefore of their capacity of restraining water for superficial tension.

There are various procedures to measure cracking, one of which is AASHTO PP34-98 “Standard Practice for Estimating the Crack Tendency of Concrete”.

A specific norm for fiber reinforced has been recently drawn up: ASTM C1579-06 “Standard Test Method for Evaluating Plastic Shrinkage Cracking of Restrained Fiber Reinforced Concrete (Using a Steel Form Insert)”.

Long-term shrinkage (hydraulic) – Long Term Shrinkage cracking

During concrete ripening the water leak goes on and that requires a volumetrical reduction: should this happen freely there would be no tensions in the structure.

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3. Fiber reinforced concrete; Basic elements for the structural project.

If, on the contrary, the structure isn’t free of shrinking, there would arise some traction tensions which can overcome the material resistant capacity causing the arising of cracks spread over con-crete.

It’s possible to get out of this phenomenon by adding to the mixture short fibers, in suitable quan-tity.

The optimum fibers in this sense are steel microfibers (Q ≤ 0.20 mm) owing to the larger specific surface and, therefore, to the possibility of interacting with cementitious matrix.

One of the procedures used to measure the effects of shrinking, in not confined conditions, is the norm ASTM C157 “Standard Test Method for Length Change of Hardened Hydraulic-cement Mor-tar and Concrete”.

At present, there are no confined condition regulations, for fiber reinforced concretes.

Durability

In the recent instructions CNR DT204 2006 it’s reproduced a table concerning steel fibers, which specifies these fibers possibilities of use according to exposure classes (in accordance with the norm EN 206-1:2006 - Concrete - Part 1: Specification, performance, production and conformity) and to penetration depth of water under pressure (UNI EN 12390-8).

Freeze-thaw

As for frost resistance of fiber reinforced mixtures with steel fibers, it must be said that just an in-crease of air pockets ratio is to be held as efficient: only by acting this way it’s possible to obtain frost resistant concretes and this is true also for fiber reinforced concretes.

Reinforced concretes with steel fibers, with suitable air contents show a very good resistance to freeze-thaw cycles in comparison with not reinforced concretes (Massazza and Coppetti, Italce-menti, 1991).

The norm to be used, ASTM C666-03 “Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing”, applies to fiber reinforced concretes, too.

In European ambit it’s possible to use the regulations CEN/TR 15177:2006 “Testing the freeze-thaw resistance of concrete - Internal structural damage”, EN 13581-2003 “Products and systems for the protection and repair of concrete structures - Test method - Determination of loss of mass of hydro-phobic impregnated concrete after freeze-thaw salt stress” or the norm UNI 7987-2002 “Concrete - Determination of deterioration resistance for freeze and thaw cycles”.

Carbonation

The presence of fibers seems not to affect meaningly the carbonation phenomenon as no increases of the depth of CO

2 face have been noticed.

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3. Fiber reinforced concrete; Basic elements for the structural project.

The measurement of fiber reinforced concrete carbonation depth is carried out by the test procedure used for ordinary concretes: UNI 9944-1992 “Corrosion and protection of concrete framework. De-termination of carbonation depth and of profile of penetration of chloride ions into concrete”. Fibers corrosion

In order to estimate the effects of the exposure of fiber reinforced concrete to aggressive environ-ments (environment saturated with salt, aggressive ions, etc.) it’s necessary to distinguish between integral concretes and pre-cracked concretes.

In the first case the corrosion is restricted to the surface fibers with just an aesthetical result.

In the case of cracked specimen, the strength lowering is moderate and depends on the crack width and depth: with crack apertures larger than 0.1 mm, but limited in depth, there are no consequenc-es on structural efficacy (ACI 544.1R – Fiber Reinforced Concrete).

Fire exposure

The following statements are integrally drawn from the Instructions CNR DT204 2006. On the basis of the experience so far acquired on the behaviour in the presence of fire of fiber reinforced con-cretes with steel fibers the following remarks can be expressed:

- Low ratios of fibers (up to 1%) don’t’ alter meaningly the thermal diffusivity, which remains therefore computable on the basis of the data available for the matrix;

- The damage caused in the material by a thermal cycle pushed up to 800 °C proves to be mainly correlated to the maximum temperature reached in the cycle and produces an irreversible effect on the matrix. This behaviour, mainly noticed in presence of limited volumetrical fractions of metallic fibers, suggests, once restore the room temperature, to rate the deterioration produced through the calculation of the remaining strength;

- As the exposure maximum temperature varies, the first crack strength proves to be basically lined up with that of the matrix. With temperatures above 600°C, the fibers improve the behaviour of the matrix;

- As the exposure maximum temperature varies, the coefficient of elasticity of fiber rein-forced concretes isn’t meaningly affected by the presence of limited volumetrical fractions (≤ 1%) of fibers and, therefore, it may be assimilated to that of the matrix;

- The presence of polypropylene fibers proves to be effective to limit the consequences of destructive spalling. In particular, such fibers partially sublimate at a temperature of 170°C leaving free cavities in the matrix. A volumetrical fraction of fibers included between 0.1% and 0.25% can meaningly mitigate or remove the phenomenon.

To verify the effects of fire exposure, there are several procedures, some of which here quoted:

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- ISO 834 – 1994: Fire-resistance tests - Elements of building construction; - BS 476 – 2004: Fire tests on building materials and structures.

3.2 - Structural compatibility of fiber reinforced concrete elements.

In principle, the use of fiber reinforced concrete is recommended above all for redundant frame-works, as the remaining traction strain can increase the total load capacity of the framework and improve its ductility.

The mechanical properties of fiber reinforced concrete must be directly determined on specimen through normalized tests.

In absence of specific tests the properties not explicitly specified below can be assimilated to those of ordinary concrete.

Here are the minimum requirements, as quoted in “Instructions for the Design, the Execution and the Control of Fiber Reinforced Concrete Frameworks - CNR DT204 2006”:

- The minimum measuring of the fibers for structural employments mustn’t be inferior to 0.3% in volume;

- The employment for structural aims of fiber reinforced concrete with deteriorating behav-iour is allowed provided that the remaining strength to traction in exercise f

Fts is equal or superior to

20% of that of the matrix fct;

- In all fiber reinforced frameworks it’s necessary to assure that the maximum load is superior of at least 20% to that of first crack; otherwise it can be at least equal or superior provided that the ratio between the maximum displacement and that of first crack is at least equal to 5;

- It’s possible to carry out monodimensional elements in fiber reinforced concrete in absence of traditional framework if, besides satisfying the previous restrictions, the fiber reinforced concrete has a hardening behaviour to traction so that the ratio between the last remaining strength f

Fts and

the matrix strength fct is at least equal to 1.05.

Graphic 3.8 - Tension vs. deformation relation.

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3. Fiber reinforced concrete; Basic elements for the structural project.

3.3 - Instructions for the design of fiber reinforced concrete frameworks.

The design of fiber reinforced concrete frameworks is based on the principles stated by the Euro-codes for concrete and reinforced concrete frameworks.

In this paragraph there will be a hint at the regulations included in “Instructions for the Design, the Execution and the Control of Fiber Reinforced Concrete Frameworks” (CNR DT-204/2006) and in the document “RILEM TC 162-TDF: Test and design methods for steel fiber reinforced concrete – s-e Design Method”.

The strength and the constitutive connection to compression of fiber reinforced concrete may be assimilated to those of ordinary concrete, therefore according to what provided in EUROCODE 2, “Design of Concrete Structures”, ENV 1992-1-2, 2003.

For the traction, if there isn’t a hardening behaviour reachable only for measurings of about 1.5–2% in volume, the traction strength is the same of the cementitious matrix fct, which may be drawn starting from the first crack strength obtained by the bending test (Instructions CNR DT204 2006 and RILEM TC 162-TDF).

The constitutive connections s - e are drawn by the curves s - e obtained by the bending tests, (UNI 11039 or RILEM TC TC 162-TDF – Bending test).

In case of hardening or deteriorating bending behaviour there are some equivalence formulae to ob-tain the values of remaining strength to traction in service fFts

and last fFtu

starting from the equivalent strengths f

eq(0-0.6) and f

eq(0.6-3.0).

In case of rigid plastic behaviour, in CNR Instructions slightly different formulae are used:

Softening(Fibers Volumen < Critical Volumen)

Hardening(Fibers Volumen > Critical Volumen)

Plastic-Rigid)(Fibers Volumen = Critical Volumen

Graphic 3.9 - Constitution law determination, tensile strength vs crack opening. Hardening, plastic-rigid and softening behavior idealization. CNR DT 204/2006.

The same can be said for the advice RILEM TC 162-TDF, with some differences in the constitutive con-nection and in the formulae which correlate the bending remaining strengths and the traction ones:

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3. Fiber reinforced concrete; Basic elements for the structural project.

fc (N/mm )2

fc (N/mm )2

(% )0(% )0

(Axial force)

Graphic 3.10 - Tension versus deformation diagram considered for RILEM TC-162).

The testings of fiber reinforced elements must be carried out both concerning the limit states of exercise (SLE), and concerning the last limit state (SLU), as determined in the regulation in force.

It must be tested, through the partial coefficients procedure, that, in all design situations, adopting the design values of actions, of stresses and of strengths, no limit state has been violated.

Therefore it must come out:

where Ed and R

d are, respectively, the design values of the generic effect taken into consideration

and of the corresponding strength in the environment of the limit state examined.

The design values are obtained from the characteristic ones, resulting from laboratory normalized tests, through suitable partial coefficients, the values of which, for the various limit states, are those recommended by the regulation in force appropriately supplemented concerning fiber reinforced concrete traction strength.

The properties values of the materials used in the fiber reinforced frameworks design must have been determined through laboratory normalized tests. The mechanical properties of strength and distortion of the materials, as it was said above, are quan-tified by the corresponding characteristic values.

The only rigidity parameters (coefficient of elasticity) of the materials are evaluated through the cor-responding average values.

The design value of the generic strength property, Xd, may be expressed in general form through a

relation such as:

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3. Fiber reinforced concrete; Basic elements for the structural project.

where X

k is the characteristic value of the generic property and g

m is a partial coefficient of the material.

In the determination of the characteristic value of the fiber reinforced concrete traction strength it’s possible to consider the structural redundancy:

where fFtm

is the middle value, k is Student’s factor, s the standard deviation while a is a coefficient which decreases when structural redundancy increases.

Testing to limit states for monodimensional elements

Combined compressive and bending stress

The design to SLU of beam elements subjected to bending requires the reckoning of the resistant last moment and the comparison with the design moment.

It’s assumed that bending cracking shows when one of the following conditions takes place:

- Reaching of the maximum compression distortion in concrete; - Reaching of the maximum traction distortion in framework steel (if present); - Reaching of the maximum traction distortion, e

Fu, in fiber reinforced concrete.

For a deteriorating constitutive connection, the maximum traction distortion is assumed equal to 2% and anyway the maximum crack aperture mustn’t be wider than 3 mm.

For a hardening constitutive connection, the maximum distortion is about 1%.

The calculation of bending and combined compressive and bending stress SLU, with or without the presence of steel bars ordinary framework, can be carried out on the basis of constitutive connec-tions simplified as in the following picture:

Graphic 3.11 - Limit states for the combined compressive and bending stress: use of the constituent simplified laws (stress-block with coefficients η e λ as EC2).

Hardening Softening(V>V )f crítico (V<V )f crítico

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3. Fiber reinforced concrete; Basic elements for the structural project.

Graphic 3.12 - Limit states for the combined compressive and bending stress: simplified method (stress-block as RILEM TC-162).

A similar approach is followed in the advice RILEM TC 162-TDF:

As already quoted, the values to be used in testing come out of bending tests in laboratory and are then converted into traction values, reduced of safety partial coefficients.

Shearing and torsion

Without going into details (it’s possible to refer to the quoted normative documents for the study in depth) it’s interesting the possibility of quantifying the contribution due to fibers (to be determined with the same procedure followed for the combined compressive and bending stress) which allows to replace, partially or totally, the shearing or torsion framework.

If the shearing or torsion strain is of little importance, the regulations require, however, a minimum framework which can be guaranteed by the fibrous reinforcement.

Testing to SLU for plate elements

For plate elements without conventional framework subjected to prevalent bending strains, the strength testing can be carried out referring to the resistant moment, m

Rd, reckoned assuming the

rigid-plastic constitutive connection:

In case of contemporary action of two bending moments m

x and m

y acting in orthogonal directions,

the testing to SLU requires the fulfilment of the restriction:

RelationFactors

Axial strenght

Equivalent resistance Relation

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3. Fiber reinforced concrete; Basic elements for the structural project.

It’s worth noticing that the resistant capacity of a plate lying on the ground, as in the case of floor-ings, would be of little importance if estimated, with a traditional approach, in tension terms, as prescribed by all regulations, and CNR Instructions aren’t an exception.

To consider properly the contribution given by structural redundancy, very high in case of ground floorings, absolutely necessary for deteriorating bending behaviours, it’s possible to work with not linear analysis methods (Yield lines method or Non-Linear Fracture Mechanics method).

Testing to Exercise Limit State

Tensions testing

The testing of compression tensions in exercise must be carried out according to the current regula-tion, as for ordinary concrete.

If the structure is made with a deteriorating behaviour fiber reinforced, the testing of traction ten-sions in exercise is implicitly fulfilled if the same structure has been tested at the SLU.

If, on the contrary, the fiber reinforced concrete has a hardening behaviour, it’s also necessary to carry out the testing of traction tensions in exercise, checking that the maximum stressing tension complies with the following condition:

Cracks aperture

In reckoning the cracks characteristic width, it’s possible to quantify the contribution given by fibers through the aliquot of the strain absorbed by the fiber reinforced for the benefit of the ordinary framework (RILEM TC 162-TDF and Instructions CNR DT204 2006).

To do this the CNR Instructions suggest to assume a constant distribution of width tensions equal to traction tension characteristic to SLE, f

Ftsk.

Minimum framework for crack control

In order to control crack, in bent elements it’s necessary to provide for a minimum framework.

In CNR Instructions the minimum framework area is equal to:

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3. Fiber reinforced concrete; Basic elements for the structural project.

where: - A

s is the stretch bending framework area [mm2]. In case As is negative, the minimum frame-

work may consist only of fibrous reinforcement; - A

ct is the concrete area of the section subjected to traction [mm2], determined assuming a

strain state to the elastic limit; - s

s is the maximum tension in the framework admissible in cracked phase. It may be as-

sumed equal to steel yield; - f

ct,ef is the traction strength to concrete effective at first crack moment [mm2]. It depends

on environment conditions. In absence of specific data, the traction strength must be considered as determined 28 days after the casting; - k

c is a coefficient which considers sectional reallocation of strains soon before the crack.

kc = 1 in presence of pure traction, k

c = 0.4 in presence of pure bending,

- ks considers the effect of not uniform autobalanced strains. In absence of precise data, this

value may be considered equal to 0.8; - k

p considers the presence of precompression:

where

is the precompression ratio, ev is the eccentricity of precompression strength resultant,

3.4 - Current standard situation.

All norms previously quoted are following. - ACI Committee - Report 544.1R – State-of-the-Art Report on Fiber Reinforced Concrete - ACI Committee - Report 544.2R – Measurement of Properties of Fiber Reinforced Con-crete

for e/h>0.4;for e/h<0.4;

In pure bending kc = 0.4 , then k

p = 1-1.5a

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- ACI Committee – Report 544.4R – Design Considerations for Steel Fiber Reinforced Con-crete - ASTM C39 - Standard Test Method for Compressive Strength of Cylindrical Concrete Speci-mens - ASTM C157 - Standard Test Method for Length Change of Hardened Hydraulic-cement Mortar and Concrete - ASTM C418 - Standard Test Method for Abrasion Resistance of Concrete by Sandblasting - ASTM C496 - Standard Test Method for Splitting Tensile Strength of Cylindrical Concrete Specimens - ASTM C512 - Standard Test Method for Creep of Concrete in Compression - ASTM C666 - Standard Test Method for Resistance of Concrete to Rapid Freezing and Thawing - ASTM C779 - Standard Test Method for Abrasion Resistance of Horizontal Concrete Sur-faces - ASTM C1018 - Standard Test Method for Flexural Toughness and First-Crack Strength of Fiber Reinforced Concrete - ASTM C1116 - Standard Specification for Fiber Reinforced Concrete and Shotcrete - ASTM C1399 – Standard Test Method for Obtaining Average Residual-Strength of Fiber Reinforced Concrete - ASTM C1550 - Standard Test Method for Flexural Toughness of Fiber Reinforced Concrete (Using Centrally Loaded Round Panel) - ASTM C1579 - Standard Test Method for Evaluating Plastic Shrinkage Cracking of Re-strained Fiber Reinforced Concrete (Using a Steel Form Insert) - CRD-C 63-80 - Test Method for Abrasion-Erosion Resistance of Concrete (Underwater Method), U.S. Army Corps of Engineers - AASHTO PP34-98 - Standard Practice for Estimating the Crack Tendency of Concrete - EFNARC - European Specification for Sprayed Concrete - EN 206-1 - Concrete - Part 1: Specification, performance, production and conformity - EN 12390-3 - Testing hardened concrete - Compressive strength of test specimens - EN 12390-6 - Testing hardened concrete - Tensile splitting strength of test specimens - EN 12390-8 - Testing hardened concrete - Depth of penetration of water under pressure - EN 13581 - Products and systems for the protection and repair of concrete structures - Test method - Determination of loss of mass of hydrophobic impregnated concrete after freeze-thaw salt stress - EN 13687-1 - Products and systems for the protection and repair of concrete structures - Test methods - Determination of thermal compatibility - Freeze-thaw cycling with de-icing salt im-mersion - EN 14651 – Precast concrete products - Test method for metallic fiber concrete - Measuring the flexural tensile strength - CEN EN 1992-1-1 - Eurocode 2 – Design of concrete structures - Part 1-1:general rules and rules for buildings - CEN/TR 15177 - Testing the freeze-thaw resistance of concrete - Internal structural damage - RILEM TC 162-TDF: Test and design methods for steel fiber reinforced concrete – Bending test - RILEM TC 162-TDF: Test and design methods for steel fiber reinforced concrete – s-e De-sign Method - RILEM CPC-18 – Measurement of hardened concrete carbonation depth - NF P18-409 – Beton avec Fibers Metalliques. Essai de flexion

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- UNE 83-510 – Determination del Indice de Tenacidad y Resistencia a Primera Fisura - NBN B 15-238 – Essai des bétons renforcés des fibers. Essai de Flexion sur éprouvettes pris-matiques - JCI–SF4 – Method of Tests for Flexural Strength and Flexural Toughness of Fiber Reinforced Concrete - UNI 7087 - Calcestruzzo - Determinazione della resistenza al degrado per cicli di gelo e disgelo - UNI 9944 - Corrosione e protezione dell’armatura del calcestruzzo. Determinazione della profondità di carbonatazione e del profilo di penetrazione degli ioni cloruro nel calcestruzzo - UNI 11039-1 – Calcestruzzo rinforzato con fiber di acciaio. Part. I: Definizioni, classificazi-one e designazione - UNI 11039-2 – Calcestruzzo rinforzato con fiber di acciaio. Part. II. Metodo di prova per la determinazione della resistenza di prima fessurazione e degli indici di duttilità - UNI U73041440 - Progettazione, esecuzione e controllo degli elementi strutturali in calces-truzzo rinforzato con fiber d’acciaio - Norme Tecniche per le Costruzioni – Decr. 14/09/05 – G.U. 23/09/05 - CNR DT204 2006 - Istruzioni per la Progettazione, l’Esecuzione ed il Controllo di Strutture di Calcestruzzo Fibrorinforzato - ISO 834 – Fire resistance tests - Elements of building construction - BS 476 - Fire tests on building materials and structures

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4 - Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Concrete is, no doubt, the material most employed by humankind in the construction of civil engi-neering works. Much testing and research has been done in order to better understand the behav-iour and to improve the performance of the material. This chapter will summarize briefly the main characteristics of the material, and identify the contribution that fiber reinforcement can provide. The aim of this chapter is to give the reader a picture of the technological aspects for the formulation of reinforced concrete with steel fibers.

Steel fiber reinforced concrete (SFRC) is simply a standard concrete mixture into which reinforcing fibers are incorporated, creating in the matrix a three-dimensional framework that significantly in-creases the post-crack mechanical strength of the concrete.

Concrete of pumped or cast kind is nowadays the most used in the greater part of appliances. When designing a concrete mixture, it is important to consider the what its use will be and whether it’s necessary more or less workability. In this chapter will be introduced, concisely, the main factors and necessary considerations for your formulation.

For the formulation of any kind of concrete, it is necessary to consider the three main variables which must be modified to reach the desired result: water/cement ratio, workability (measured by Abrams’s cone) and cement content. The interaction of these three variables allows the designer to achieve a specific concrete strength. Any variation in one requires the others to vary accordingly if the same strength is to be achieved (See Figure 4.1).

4. 1 - Concrete, technological aspects for its formulation.

STRENGTH

WATER/CEMENT RATIO

WORKABILITY QUANTITY OF CONCRETE

Figure 4.1. - Base relation between the parameters which affect the mixture.

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The relation existing between these three variables may be determined with reasonable precision through the following equation:

Where:c = cement content (kg/m3)a = a/c = water/cement ratio (1/kg)T = Slump of Abrams’s cone (cm) K, m e n are variables which depend on the kind of aggregate used.

This equation is known as the triangular ratio. Together with Abrams’s law (workability), these rela-tionships form the two main laws which must be considered for the design of concrete mixture using the method presented in this handbook.

At present, there are many design methodologies proposed for the design of concrete mixtures. For the purpose of this handbook, a method with a general character has been selected that has been used and proven on many occasions. The method has been developed for use in the design of com-pression strength concretes (average strength after 28 days of age, in cylindrical test tubes of 15 cm of diameter and 30 cm of height) between 18 MPa and 42 MPa and Abrams’s cone lowering between 2,5 cm and 18 cm. For concrete mixes that differ from these stated conditions, it is recommended to use another design methodology.

The methodology which follows will be proposed in summed up form, if there’s the wish of analysing better this subject it’s advisable to see the corresponding regulations.

Entry data

1) Strength

The calculation strength or characteristic strength will have to be equal to compression strength ex-pected by the designer, increased through the following equation (strength measured in test tubes of 15 cm of diameter and 30 cm of height):

Where:Fcr

= calculation compression strength or characteristic strength.f´

c = compression strength expected by the designer.

Z = student’s variable of normal distribution (see Table 4.1).s = deviation expected for concrete (see Table 4.2).

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Table 4.2 - Ratio between control degree and standard deviation.

2) Workability

It has to be calculated through Abrams’s cone. It must be considered that the more it’s difficult to cast concrete, the greater the expected lowering will have to be. Table 4.3 shows the usual values of lowering to the cone:

Table 4.1 - Frattili and values of Student’s variable Z correspondent.

Table 4.3 - Typical values for slump.

FRATTILE % Z

20

10

5

0,842

1,282

1,645

CONTROL DEGREE WITHOUTCONTROL BAD MEDIUM GOOD EXCELLENT

STANDARD DEVIATION

STANDARD DEVIATION

MPa

kg/cm2

9,0

>92

6,5

66

5,0

51

4,0

41

3,0

31

Element Design Slump (cm)

Prefabricated building

Huge foundations

Reinforced pedestals and foundation walls

Floors

Plates, beams, columns, edgewise walls

Thin structural walls

Carried by pumping

Superplasticized

None

3

4

5

6

10

6

6

8

8

8

11

18

18

Greater than 18

3) Aggregates maximum dimension

The maximum aggregate dimension will have to be selected according to the application of the structure and the type of structure being designed. The maximum aggregate dimension should not be more than ½ of the minimum dimension of the element to be produced, nor should it be more than ¾ of the spacing distance between two adjacent pieces of reinforcement.

3

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Normally the maximum dimension of the aggregate varies between 20 and 50 mm; if aggregates of greater dimension are used, there will be a tendency for the mixes to segregate. For high strength concretes, reduced maximum dimensions are recommended. 4) Aggregate gradation limits

In concrete there must be aggregates of different dimensions, allocated so as to minimize the con-tents of interstitial voids. On this subject there are many theories about the optimum combination or better granulometry which must be adopted in a definite design. Table 4.4 presents granulometrical limits suitable for aggregate of different maximum dimensions.

5) Ratio b

It represents the weight of sand expressed in percentage in ratio with the aggregates total weight to be found in the mix (sand + coarse aggregate) and is expressed through the following equation:

This ratio must be such as to include the granulometry in the zone recommended in Table 4.4.There are several methods for the correct calculation of b, the easiest and quite precise it’s the graphic method which can be found in the usual bibliography for the formulation of concrete.

6) Abrams’s law

This law fixes the correlation existing between concrete strength and the relation of water content/cement in weight, the expression of which is called a:

Where:a = water weight;c = cement weight.

Abrams’s law can be expressed as:

where:R = strength to a defined age of ripening;

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Table 4.4 - Gradation limits recommended for different maximum dimensions of the aggregate – passing rates.

If from the expression 37 the unknown a is made explicit, the result is:

For coarse aggregates of 25.4 mm of maximum dimension, natural sand (both in saturated condi-tion with dry surface) and Portland cement Type I of a medium quality, good approximations are obtained with:

a) R7 = 902.5 / 13.1a ; a = 1.724 – 0.3887 Ln R

7 ; (MPa)

b) R28

= 88.50 / 8.69a ; a = 2.073 – 0.4628 Ln R28

; (MPa)c) R

90 = 95.43 / 7.71a ; a = 2.232 – 0.4896 Ln R

90 ; (MPa)

Formule 37. Specific Abrams Low.

7) Correction of a

In case the conditions of M and N aren’t those expected originally, there is a factor KR the aim of which

is to fit the values of a to the different kinds of aggregates. Refer to Table 4.5 and Table 4.6.

Sieve(mm/inches)

Maximum dimension(mm / inches)

88,9mm

3 / ''1 2

76,2mm

3 ''

63,5mm

2 / ''1 2

50,8mm

2 ''

38,1mm

1 / ''1 2

25,4mm

1 ''

19,0mm

/ ''3 4

12,7mm

/ ''1 2

9,53mm

/ ''3 8

6,35mm

/ ''1 4

---------

100-9062-5238-2621-98-25-12-0

--------

100-9073-6162-4840-2626-1413-57-35-1

3 ''3''

22

11

48

163050

100

1

1

1

3

1

3

1

/

/

/

/

/

/

/

2

2

2

4

2

8

4

''''''

''''''''''''''''''''''

88,9mm76,2mm63,5mm60,8mm38,1mm25,4mm19,0mm12,7mm9,53mm6,35mm4,76mm2,38mm1,19mm0,595mm0,298mm0,149mm

100-9095-8092-6085-5076-4068-3363-3057-2853-2545-2245-2240-2035-1525-1016-78-2

-100-9092-7087-5580-4572-3868-3562-3558-3048-2548-2543-2035-1525-1016-78-2

--

100-9087-6580-5573-4768-4362-3760-3558-3050-2845-2035-1525-1016-78-2

---

100-9087-7377-5973-5368-4465-4060-3555-3045-2035-1525-1016-78-2

----

100-9084-7077-6170-4965-4360-3555-3045-2035-1525-1016-78-2

-----

100-9090-7075-5568-4560-3555-3045-2035-1525-1016-58-2

------

100-9085-6575-5565-4560-3845-2035-1525-1016-58-2

-------

100-9078-9065-5158-4243-3731-1720-1011-56-2

M and N: they are constants which depend on the characteristics of the materials component the mixture and on the test age.

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Page 54: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Table 4.5 - KR, factors to correct a for maximum dimension, mm (inches).

Table 4.6 - KA, factors to correct a for kind of aggregate.

Once calculated, it is necessary for the correction factors KR and K

A to be applied according to the

kind of aggregate to be used so as to obtain a more precise value

8) Limits of a for durability

It’s important to consider that a must be within certain limits, as this factor affects concrete durabil-ity. In case a exceeds these values, its value will have to be considered as the maximum allowable. See Table 4.7.

Table 4.7 - a maximums for different conditions of services or environments.

9) Triangular ratio

Through this law, it is possible to correlate three of the most important parameters which are typical of concrete, water/cement ratio (a), quantity of cement (c) and slump through Abrams’s cone.

Dimension

Maximum

Factor KR

6.35

(1/4)

1.60

76.1

(3)

0.74

64.0

(2 ½)

0.78

50.8

(2)

0.82

38.1

(1 ½)

0.91

25.4

(1)

1.0

19.0

(3/4)

1.05

12.7

(1/2)

1.10

9.51

(3/8)

1.30

Natural sandGround sand

1.001.14

0.971.10

0.910.93

Fine

CoarseGround Half-ground Cobblestone

(natural gravel)

0.75

0.60

0.55

0.50

0.40

0.45

0.65

According to case

Deterioration ofconcrete andcorrosion offrameworks

Deterioration forwashed out.permeability

Kind of damage Conditions Maximum

,

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4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Where K, n and m are constants which depend on the characteristics of the materials being parts of concrete.

Similarly to the case of a, in the situation where concrete is formed by coarse, round aggregates of 25.4 mm of maximum size, natural sand (both in saturated condition with dry surface) and Portland cement Type I of a medium quality, good approximations are obtained with:

is expressed in cm and c in kg/m3.

10. Correction of c

Similarly to the case of a, in the event of using other characteristics different from those previously described for concrete components it’ll be necessary to use Tables 4.8 and 4.9 to correct the quantity of cement to be used.

Table 4.8 - C1 factors to correct c in function of the maximum dimension, mm (inches).

Table 4.9 - C2, factors to correct c for kind of aggregate.

And, as in case of a, the quantity of cement will never have to be inferior to the values shown in Table 4.10

(39)

c = 117.2 . . T-1.3 0.16

Dimension

Maximum

Factor KR

6.35

(1/4)

1.33

76.1

(3)

0.82

64.0

(2 ½)

0.85

50.8

(2)

0.88

38.1

(1 ½)

0.93

25.4

(1)

1.0

19.0

(3/4)

1.05

12.7

(1/2)

1.14

9.51

(3/8)

1.20

1.001.28

1.031.23

0.900.96

Fine

CoarseGround Half-ground Cobblestone

(natural gravel)

Natural sandGround sand

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Page 56: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

11) Calculation of the remaining components

Any mixture design is carried out on the basis of one cubic metre (1000 litres), therefore it’s neces-sary to consider the other components which form concrete. As the aim of this handbook isn’t that of give specific details, the remaining components will be briefly described.

- Included air:

Where:V = volume of included air c = quantity of cement (kg/m3)P = maximum dimension of aggregates (mm)

- Cement absolute volume:

It’s equal to the weight of the material divided by its specific gravity, it’s a value which must be cal-culated in laboratory, for the aim of this handbook it’s sufficient to know that, in normal conditions, this value is equal about to 3.3, the opposite of which is 0.3.

- Water absolute volume (kg/m3)

Considering that water specific gravity is equal to 1.

- Aggregates absolute volume

It corresponds to their weight, divided by their respective specific gravities. These specific gravities will have to be calculated in laboratory; for the aim of this handbook it’s sufficient to know that, in normal conditions, this value is on average near to 2.65 both for big aggregates and for sand.

Table 4.10 - Minimum contents of cement according to environment al service conditions.

Quantities of cement(kg/m )3

In sea aggressive environments. etc. orin concretes subjected to deterioration

.

270

350

Service or environmental conditions

In any circunstance (massive concretes are a special case)

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Page 57: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

12) Final calculation of mixture

As said before, the mixture design must be carried out on the basis of 1 cubic metre, therefore, the sum of components will have to be equal to unity;

Where:g

(G + A) = Specific gravity of the combined aggregate. This value can be calculated on the basis of b

through the following expression:

; ( b < 1)

Finally, drawn A + G from formule 42 and using ratio b, each of the weights can be obtained sepa-rately;

Evidently, as already previously explained, the method shown in this handbook is rather simplified and doesn’t consider many other factors which may come into play when designing a mixture, neverthe-less it sums up, in a simple way, the main steps to follow for concrete formulation.

(42)

(G+A)(G+A)

+ 0.3.c + a + V 1000 litros

(44)

G+A = 1000 - (0 3 c + a + V) . . .G+A

G+AA =

A....G

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Page 58: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

4.2 - Advice for the incorporation of fibers in concrete.

Fiber Reinforced Concrete is simply a standard concrete mix with an additional component, reinforcing fibers. For the mixture production, the fiber must be considered as an additional aggregate; it is necessary to slightly modify the components after adding these in the mixture design. The initial considerations to obtain specified compression mechanical strength and the breaking modulus remain valid.

There is fundamental advice to control the addition of fibers in a mixture which meet the suitable geometrical selection of the element, to avoid some problems such as segregation, agglomeration and assuring then a uniform distribution. There follow such fundamental rules which are valid for any kind of concrete and for any appliance:

- The length of the selected fiber will have to be greater than double maximum dimension of the aggregates with 20% tolerance.

q max > 0.5 LFiber

, com uma tolerância de até 20%.

Example: aggregate maximum 1” (25 mm) of diameter, would require a fiber of 2” (50 mm) of length, with a variation not superior to 20% of length (40 mm < L

Fiber< 60 mm).

- The fiber length will be defined in function of the minimum dimension of the structural element, according to the following ratio:

Smin ≥ 1,5 LFiber

For this rule, too, a 20% tolerance can be accepted.

- It will be necessary to consider the minimum measuring advised according to the current regulation of the country where the fiber is used. It’s never advised to use less than the following measuring of steel fibers:•MinimumMeasuring:20kg/m3 (0.25%V) for not structural elements.•MinimumMeasuring:25kg/m3 (0.3%V) for structural elements.

As we have commented for previous rules, which can be applied to any kind of concrete, some hints in function of the peculiarities of mixtures for cast on site concretes are following.

These concretes must have a workability compatible with the difficulty of their allocation and the general advice for fibers applications is to consider an additional lowering of 1” (25 mm), to make up for the loss of workability which can occur owing to fibers forming a minimum interblocking. Such a device is valid for measurings which go from a minimum of 20 kg/m3 to a maximum of 45 kg/m3. Clearly all that follow the basic rules of fibers geometrical selection, and non-keeping them may substantially damage the result with the possibility of causing problems such as, for instance, segregation and agglomeration.

The lowering expected in the reference schedules previously shown, will have then to be increased no more than 1” (25 mm), and the workability will have to be obtained with concrete plasticizing admixtures.

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Page 59: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Fibers can be incorporated in the mixture in two ways:

Incorporation into batched mixture at site. The fibers are added directly into the truck mixer prior to placing into the concrete formwork. In this particular case, it is advisable to specify the mix workabil-ity/slump before and after the incorporation of fibers in the mixture, and to conduct field testing to verify. In any case, following the hints previously given, there mustn’t be any problems of workability caused by adding fibers.

Photo 4.1 - Mechanical addition in the truck mixer. Photo 4.2 - Manual addition to the truck mixer.

Photo 4.3 - Appearance of wet concrete mixture after adding fibers. Photo 4.4 - Slump testing after adding fibers.

Insertion with the aggregates at batching plant. The fibers are incorporated with the dry aggregates during the batching of the concrete mix. In this case, it is important to specify the correct water/ce-ment ratio in order to obtain the desired workability. The design slump can vary up to +/- 25 mm.

Photo 4.5 - Manual insertion with the aggregates in the belt conveyer.

Photo 4.6 - Slump testing of batched concrete mixture.

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Page 60: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Photo 4.7 - Manual insertion in the concrete mixer. Photo 4.8 - Slump testing of batched concrete mixture.

The use of fiber reinforced concrete cast on site does not require the additional use of specialized equipment. Equipment normally used, such as vibrators and pumps, is all that is required. Special care is required when using pumped concrete mixes in order to avoid clogging. The fiber length must not exceed 70% of the diameter of the exit mouth of the pumping system.

Presented below are photos of fiber reinforced concrete mixes being poured in various conditions and using different types of equipment.

Photo 4.9 - Casting directly from truck mixer. Photo 4.10 - Casting directly from truck mixer.

Photo 4.11 - Placing pumped concrete. Photo 4.12 - Discharging concrete mix into pump hopper.

Concretes poured in the field typically have slumps ranging between 100-150 mm and water/cement ratios of 0.3-0.5. The choice of the aggregates and their granulometry will have to suit the element to cast and will be affected only by the structure and the mechanical strength required by the design, so the choice of the fiber will have to be compatible with these bases.

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Page 61: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

4.3 - Advice for insertion of fibers into concretes for prefabricated elements.

In the previous sections, it has been widely described the manufacture of mixtures with the addition of fibers, and the fundamental rules to avoid problems of segregation or fibers conglomeration. The flexibility of the insertion of fibers into the mixture is so wide that can generate concretes with very low ratio water/cement, in this particular case, the rules of fibers configuration and geometrical se-lection are of maximum importance. Nowadays, the steel fibers of loose format can be incorporated to dry mixtures without harming homogeneity.

In the case of concrete mixes with a low water/cement ratio, the role of the additives is to keep the mixture workable and to obtain a suitable finish of the precast elements.

The suggestion for these types of mixes is to use fibers with low high aspect ratios. This will avoid fiber conglomeration during the dry mixing process that can prevent the development of uniform fiber distribution in the mix. It is generally accepted that fibers with high aspect ratios have a greater tendency towards conglomeration; there are few producers that have been successful in controlling this phenomenon.

One possible solution to control the tendency to conglomerate of high aspect ratio fibers is to use fibers that have a thin coating of glued. This approach is problematic in the case of low ratio water/cement mixtures, as the small quantity of water cannot thin completely the glue resulting in a certain amount of conglomeration of fibers. The use of plasticizing admixtures in this case can help improve this situation.

As previously mentioned, the presence of the fibers in the concrete mix does not require the use of specialized production equipment. Standard concrete batching facilities are used and the fibers are incorporated as an additional aggregate, as shown in the photos below:

Photo 4.13 - Example of dry mixture with fibers. Photo 4.14 - Mixer in a precast concrete plant producing dry mixture for vibrocompressed concrete.

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Page 62: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Photo 4.15 - Batching of dry mix for vibrocompressed concrete. Photo 4.16 - Incorporation into the pump.

Photo 4.17 - Batching of dry aggregates for ashlar concrete. Photo 4.18 - Introduction into the pump.

4.4 - Recommendations for the use of fibers into wet and dry sprayed concretes.

In case of mixtures used in the manufacture of precast concrete elements, it is possible to sometimes use higher slump mixes than normally used for cast-in-place structures. The considerations previously stated for cast-in-place concretes must be followed.

The selection of aggregates and their gradations are generally controlled by the dimensions of the precast elements to manufacture. The choice of fiber used in these mixes should be compatible with the element dimensions and aggregates used.

A sprayed mixture of sand, water and cement commonly referred to as shortcrete or gunite has been used for almost a century in the field of civil engineering. The materials used in the formulation of the mix are the same as in traditional concrete mixes, only the method of application differs – pneumatic spraying instead of casting.

There are two general methods of applying shotcrete mixtures, wet or dry. In the dry method, sand, gravel and cement are worked in a mixer and then conveyed through pipes using pressured air. In the wet method, the mixture is conveyed through pipes as well, but water is introduced at the point of discharge.

A combination of the wet and dry methods of shotcrete application is also used. A small amount of water is incorporated into the mix during batching. The resultant ‘damp’ mixture is conveyed through pipes and onto the work surface by pressured air. This procedure is in common usage throughout the world. In some countries, it is the only method used.

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4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

There are numerous fields where shotcrete technologies have been applied. The ease of use of its manufacture and the advantages it offers in approaching in quick and effective way places difficult to be reached in another way, are some of the reasons for which this procedure was and keeps on being used all over the world. Typically applications are:

- Building of tunnels. - Mining industry. - Slope facing. - Stabilization of excavations for foundations. - Clearance works.

Generally, shotcrete can be used in any kind of work directed to pursue the stabilization or the covering of an irregular superficial layer where the conventional formwork cannot be used. Although the pri-mary application is that of soil support, it can be used in the general repair of concrete structures.

GENERAL ASPECTS OF MIX DESIGN

As it has already been stated, the composition of shotcrete is similar to that of conventional concrete mixes. There are, however, some differences, including:

- Low water/cement ratio. - Lower quantity of water. - Lower quantity of cement. - Maximum aggregate of 16 mm.

Regarding the water/cement ratio, it is necessary to mention the differences between the two appli-cation procedures. For the dry application method, the water/cement ratio is calculated considering not only the water which will be added to the pipe mouth, but also the moisture content of the ag-gregates used in the mix. Nevertheless, in this procedure there isn’t a definite value for the aforesaid ratio as the worker who controls the pipe is the same who controls the quantity of water which will be discharged, which is a disadvantage. Just the physical characteristics of concrete get Water/Cement ratio not to be so changed, because in case such proportion isn’t between the allowed values either there will be an excess of powder (in case of water shortage) or concrete will not fix to the surface (in case of water excess). Such ratio varies normally between 0.4 and 0.5.

In the damp way procedure, the Water/Cement ratio keeps the same levels as the dry way procedure, the difference is that, as the mixture has been manufactured previously, it’s possible to control such ratio from the beginning.

Owing to the fact that, in most cases, gunite is used through damp way, this will be the method of most reference in this chapter.

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Page 64: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

As for aggregates composition, it’s important to pay special attention, as for any kinds of concrete, to their quality. In order to obtain good results it’s necessary to have a good granulometric distribu-tion of the aggregates. Some of the criteria on which it’s impossible to skip at the moment of using shot concrete are:

- The aggregates maximum dimension mustn’t exceed 16 mm and, in any case, it’s advisable that parts larger than 8 mm don’t exceed 10% of the total, otherwise there will be an excessive bounc-ing when these get in touch with the surface.

- The aggregates granulometric curve is of maximum importance, none of the fragments will have to exceed 30% of the total weight. It will be necessary to pay special attention to the inferior sec-tion of the curve, the finest aggregates (Sieve no 0.125) will have to be between a minimum of 4% and a maximum of 9%. In case there is an excess of fine material there would occur segregations which would cause obstructions of the pipe. A shortage of the material will cause on the contrary that mixture loses cohesion interfering on the last concrete strength (See Graphic 4.1).

- The use of additives has the aim of improving the material conditions, such as for instance:

- Increasing setting quickness. - Improving concrete workability. - Improving aggregates distribution. - Reducing bouncing.

Given the importance and the variety of the additives existing on the market, this subject has been left for a separate chapter. For more information see chapter 3.1 and 3.2.

- The insertion of fibers distributed homogeneously in concrete, on one hand proves to be extremely effective to contrast the phenomenon of shrinking crack and, on the other hand, gives the concrete a ductility which may become remarkable insofar as the fibers strength is increased. For further information see chapters 3.1 and 3.2.

As peculiarity of the dry way procedure, the fibers incorporation isn’t very spread as they then bounce in great quantity (up to 50%).

Graphic 4.1 - Recommended granulometric curve for shot concrete.

Sieve ISO

Detei

nrate

(%)

Sieve ASTM (mm)

. . .

. . . . . . . . . .

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Page 65: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Table 4.11 - Selection of aggregates in function of the sieve for a shotcrete mixture.

Shotcrete application equipment

The specification and selection of the type of equipment used to apply the shotcrete is as important as the selection of the suitable components from which form the concrete mixture. Depending on the procedure used (wet or dry process) there are substantially two different kinds of equipment.

Dry process:

There is on the market a wide range of mixers for this use, anyway all are based on the same prin-ciple. The aggregates mixture must be poured into the hopper designed for such aim (Figure 4.2(A)). Insofar as the mixer turns (See Figure 4.2 (B)) the aggregates begin to fall and to fill the ejection zone and, in the end, through an air pressure between 3 and 6 bars, are shot through the conveying pipe which ends into the mouth where they are mixed with water (See picture 4.2 (C)).

A

B

P

PC

Water way out

ggregates way out

A

Figure 4.2 - Diagram of equipment for dry mixture. On the left diagram of mixer machine: A. Material, B. mixture rotor, C. pipe way out nozzle, P. pressure from the compressor to pump the mixture.

0.149 0.125 4 12

0.297 0.25 11 26

0.595 0.5 22 50

1.19 1 37 72

2.38 2 55 90

4.76 4 73 100

9.51 8 90 100

19 16 100 100

38.1 32 - -

76.1 64 - -

Tamiz ASTM (mm) Tamiz ISO Min. % Max. %

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Page 66: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Photo 4.19 - Introduction of aggregates into the mixture. Photo 4.20 - Introduction of fibers into the mixture.

Photo 4.21 - Coming out of dry mixture from the mixer. Photo 4.22 - Material conveyance by belt.

Photo 4.23 - Material conveyance by belt. Photo 4.24 - Material conveyance by belt.

Here follows a photographic sequence of preparing and using of concrete mixture with dry way process:

Photo 4.25 - Aggregates belt and spraying equipment. Photo 4.26 - Detail of spraying equipment.

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Page 67: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Photo 4.27 - Mixer detail. Photo 4.28 - Pumping of mixture into the system.

Photo 4.29 - Detail of spraying with insertion of water in the way out nozzle.

Photo 4.30 - Detail of spraying with insertion of water in the way out nozzle.

Damp process:

At present, the pumping mechanisms of the equipments used for spraying concrete through damp way use two kinds of systems: a) a spiral system which pumps the flow of concrete or b) a system of plungers which, through pressure, expel the mixture from the conveying pipe.

It’s important to point out that in damp way procedure the mixture must be prepared before being incorporated to the machine (including corresponding water). This mixture must be enough fluid to avoid obstructions of the pipe, it’s advisable the use of additives to increase concrete fluidity at the moment of pumping.

Here follows a photographic sequence of preparing and using of concrete mixture with damp way process:

Photo 4.31 - Fibers loose for the mixture. Photo 4.32 - Insertion of fibers into the truck.

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Page 68: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Photo 4.33 - Ready damp mixture. Photo 4.34 - Ready mixture with fibers uniformly distributed.

Photo 4.35 - Check of lowering (slamp). Photo 4.36 - Notice the mixture homogeneous distribution.

Photo 4.37 - Incorporation of mixture into concrete pump. Photo 4.38 - Incorporation of mixture into the pump.

Photo 4.39 - Spraying with manual nozzle. Photo 4.40 - Spraying with manual nozzle.

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Page 69: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

Spraying techniques

As already pointed out, being shot concrete a method of application, its correct carrying out is as important as the mixture composition. An uncorrected carrying out leads to a faulty result.

With a good application of Shotcrete a conglomerate with the characteristics required by the designer is obtained. The uncorrected carrying out may lead to a bad distribution of the components, excessive waste or bouncing, bad allocation, among the other unwanted factors.

In order to finish this chapter there will follow some of the most important recommendations which will have to be respected during the gunited:

Photo 4.41 - Worker who keeps the perpendicularity between the surface to gunite and the position of the plain of the nozzle mouth.

Angle of incidence:

The angle of incidence through which the concrete casting is going to reach the surface must be perpendicular to the surface itself. Otherwise, the quantity of bouncing material (wasted material) will be excessive. For this reason, the mouth of the conveyance pipe will always have to be perpen-dicular to the surface.

Velocity of impact:

The distance between the mouth and the surface is of great importance; this distance is directly pro-portional to the way out speed of concrete that is, the faster it is, the greater the distance will have to be and vice versa. So, in case the velocity of impact is very high there will be an excess of bouncing preventing that concrete gets fixed effectively to the surface, on the contrary, owing to absence of cohesion, the mass of concrete won’t get fixed to the surface causing wide leaks.

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Page 70: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

In order to reach a balance in this relation, it’s advisable to add some air at the rate of 7-15 m3/min at a pressure of about 7 bars in the end mouth and, in this situation, the distance between the pipe and the surface will have to be between 1 and 2 meters.

Selection of the suitable worker:

As it can be seen in the two previous recommendations, much of the responsibility is charged to the worker who uses the pipe (both manually and through a robot), the choice of the right person for the gunited is of great importance, as he largely affects the final result (nozzle allocation, distance of separation, quantity of water in the dry way process, etc.).

Photo 4.42 - Gunited with robot. Photo 4.43 - Manual gunited with pipe.

4.5 - Concrete admixtures and their compatibility of use in fiber reinforced concrete.

In the application of Fiber Reinforced Concrete (FRC), there are common considerations on the ap-plication of additives in the mix-design which aren’t different from those commonly adopted for mixtures of simple concrete.

Here are following, according to the technological aspects of mixtures formulation on the basis of the different applications previously described, the additives which can be used.

- Plasticizers and retarders. As their names imply, these admixtures are used to control the workability of the concrete mix. They are normally they are based on Sulfonato Naphtalene, Vinyl Copolymers, Modified Policarboxilati. They can keep the concrete workability from 2 to 6 hours, according to the mix design requirements. These additives are incorporated, once the mixture has been prepared, to control the time of workability when there are difficulties of access to the place of shotcrete or in case of long way stretches of concrete up to arrive at the work. Liquid format.

- Setting accelerants. These admixtures are setting accelerants and are incorporated to the mixture to obtain a rapid increase of strength. Normally they are products derived from silicates and aluminium sulphate. It is important to control the rate of application of these chemicals as excessive use for a prolonged period of time can reduce the material strength. A typically dosage rate is 4% to 6% of the cement fraction. The format may be in powder or liquid.

- Corrosion protectors. This is a newer class of additives that can be used to inhibit chloride ions reactions within the concrete.

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Page 71: Manual beton armat cu fibre

4. Design and detailed considerations for concrete mixtures; advice for fibers incorporation into the mixture.

The additives discussed above are in common usage in the design and batching of concrete mixtures. There have been no interaction problems reported with the use of fiber reinforcements. The addi-tives control the mixture quality and workability; the fibers are a reinforcement. The fiber dosage in a concrete volume does not appear to represent a workability problem requiring additional methods of control.

4.6 - Typical applications of the structural and not structural fiber reinforced concrete.

Starting in the1960’s, the technology of steel fiber reinforced concrete has evolved from lab experi-mentation done in the 1950’s, into practical industrial applications. Examples of the various applica-tions are monolithic prefabricated elements, industrial floors, the supports of surface and subsurface excavations using shotcrete, and prefabricated tunnel lining segments. Steel fibers reinforcement is now accepted as a viable alternate to conventional reinforcing steel.

The steel fibers were initially incorporated to the concrete matrix in order to avoid brittle behaviour and improve its physical characteristics. Under normal conditions concrete, will tend to crack, mainly owing to the traction forces which are internally produced. In order to avoid this phenomenon, it is necessary to reinforce the concrete either with welded wire mesh or with fibers. The advantage of using fibers is that the fibers will blend into the matix, creating a three-dimensional framework, avoiding then the phenomenon of plastic shrinking.

Additional research has concluded that fiber reinforcement not only improves the physical proper-ties of the concrete, but also improves the mechanical characteristics. These improvements allow the fibers to used as structural reinforcement in many cases.

There are many cases in which fibers can be and are used as structural reinforcement. Nevertheless, the lack of a clear and simple regulation is the greatest restriction limiting this “new” technology to be able to spread among a greater number of engineers and applications.

4.7 -Current standard situation.

There are many different standards and codes involved in design and manufacturing of concrete mixtures. These documents have been previously presented in chapter 3 of this handbook, and cover such phases as:

- Mixture design. - Fibers, regulations for their incorporation in different production processes. - Control of material mechanical properties. - Structural design codes.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

When great length and constant geometrical properties are characterising elements for the project design of an underground tunnel, conditions are in principle suitable to choose for a mechanised construction through the use of a TBM (Tunnel-Boring Machine), which can be adequately selected between the ever increasingly wide range of ever more versatile design alternatives.

5.1 - Conventionally bored tunnels and tunnels excavated through TBM.

Photo 5.1 - Tunnel obtained through TBM of 12 m diameter, Line 9 of the metro in Barcelona, Spain.

In the almost total number of cases, this mechanised excavation procedure is associated to the use of lining rings made of precast segments of reinforced concrete. These segments are adequately as-sembled within the underground tunnel systematically and continuously throughout the advancement of the excavation works in such a way that the tunnel turns out to be completed after the passage of the TBM.

Photo 5.2 - Precast ashlars for TBM tunnel construction, Line 9 of the metro in Barcelona, Spain.

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However, when we decide by the conventional excavation of a tunnel, be by means of the explosives use or resorting to mechanical removal of the soil, generally we procede immediate stabilization of the exposed cavity with the front advance of excavation, where are placed supports, characterized by your technological compatibility in the extensive use of the projected concrete. These supports are eventually integrated for metallic structures elements, such as anchorages and profiles. (It is then placed a support by the construction of which current technology does extensive use of the shotcrete, eventual integrated with metallic structural elements, which are the anchorages and the profiles).

Photo 5.3 - Example of a tunnel obtained through conventional excavation with explosives. Railway line Caracas-Charallave, Venezuela.

Photo 5.4 - Example of a tunnel obtained through conventional excavation with explosives, place-ment of metallic support. Railway line Caracas-Charallave, Venezuela.

Right after or even immediately after tunnel excavation has been completed, the cavity is generally, although not necessarily, covered through an on-site casting of completely or partially reinforced concrete, which function may vary from rigorously structural to purely “cosmetic”. This depends from the geostatic and functional conditions of each specific work.

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For all the above sequentially mentioned elements, such as the precast concrete rings, the primary supporting structures in shotcrete and the linings of cast-in-place concrete, modern technology of structural concrete makes use of metal fibers, either in substitution or in addition to conventional reinforcement metal bars, ever more frequently and with ever increasing comparative advantages and excellent results. Metal fibers may be eventually also complemented through the use of synthetic fibers.

Photo 5.5 - Example of tunnel obtained through conventional excavation with explosives, which final lining is obtained though on-site concrete casting. Railway line Caracas-Charallave, Venezuela.

5.2 - Design criteria for tunnel supports and linings.

The geostatic behaviour of an underground excavation depends, between many other factors, on the geomechanical characteristics of the working environment, on the natural stresses which were already present in the environment, on the adopted construction process and constructing proce-dures, thus including the nature of the construction support which has been eventually installed, and the specific circumstances in which the installation was made. The aforesaid reflects in what is appropriately defined as “type of behaviour of the excavation” that comprehends, between other factors, the geomechanical concretization of the environment (the geomechanics of the rock mass to be excavated) as well as the definition of the status of natural stresses (as function, in a first instance, of the depth or covering of the tunnel and of the density of the rock mass).

The initial, or primary phase, support shall guarantee safety conditions for workers and (possibly to-tal) stability of the cavity in the short term. It is generally put in place in uncomfortable, hostile and even dangerous environmental conditions, which render controls over its quality generally limited and sometimes even insufficient. As a result, it is recommended not to assign a formal long-term structural reliability to such initial lining, but only an immediate and temporary task of support in guaranteeing structural integrity. A conservative initial lining (such as made up of shotcrete containing metal fibers, metallic ribs or sewing or fixing spiles) may be integrated with elements for mechanical strengthening (for improvement) of the rock mass (such as e.g. metal spiles, glassfiber composite, injections, etc.) or alternatively, with elements having pre-supporting function (such as e.g. truncated cone archs of concrete in pre-shear, or jet-grouting, or microspiles). These criteria may be applied each

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time that such an integration may result necessary or beneficial towards improving safety conditions and achieving an adequate control over stabilization of the cavity in the short term, concurring at the same time to the establishment of more efficient static conditions in view of the exploitation of the final lining’s functions.

The deformation of the advancing nucleus of the excavation represents a fundamental element in the control of stability of the excavation. Thus, controlling and limiting deformation of the advanc-ing nucleus (extrusion) by appropriately increasing its rigidity plays a fundamental role in the whole tunnel’s stability both in the short and in the long term. This derives all from the proven existence of a strict relationship between the phenomenon of nucleus’s extrusion at the excavation advancement face and the phenomena of pre-convergence and convergence of the cavity, where a chronologic dependence exists between phenomena of deformation of the cavity and those preventively impact-ing the nucleus at the excavation face. Analogously, an equally strict relationship exists between the instability or collapse of the excavation face or advancing nucleus and the consequent instability or collapse of the cavity, though preventively stabilized.

The final lining shall guarantee that the adequate safety factor or the reliability defined for the work are achieved, thereby absorbing loads estimated to be applied to the lining in the long term, fol-lowing criteria defined to the purpose. Between those loads, at the beginning, seismic actions will not be included, unless it is dealt with specific sections corresponding to situations considered to be particularly sensitive to seismic actions, such as e.g. it happens for tunnel sections located close to the surface or for tunnel sections excavated in particularly unfavourable geologic sectors (fault fractures, etc.). In the lining sections where reinforcing steel is not requested to be applied to absorb static tensile stresses, steel will be placed to control cracking due to shrinkage.

In case tensile stresses are limited and in case reinforcing steel is only requested to be applied to control cracking due to shrinkage, reinforcing steel can be advantageously applied in form of metal fibers in the adequate quantity. When the lining is not to be directly applied to fulfil structural require-ments, its functions will be, between others: to facilitate natural ventilation, to guarantee geometric regularity of the section, to contribute to waterproofness. In these cases, the lining thickness will be limited to minimum values compatible with technological requirements (in the order of 30 cm), and, in those cases, the quantity of reinforcing fibers to be applied will be limited to minimum values foreseen by standards (25 kg/m3).

Procedures to be applied for excavation, as well as for the support and the lining, shall be selected in such a way that they will result statically efficient, feasible from the point of view of construction, and ideal from an economic perspective. As a result, at the beginning, they will be characterised by a horseshoe profile, or by a single arch of a circle, except for the upper part, which will be adequately selected for each sector of the tunnel, thereby ranging from flat to curve, with same radius as the rest of the tunnel section perimeter, inasmuch as the geomechanical quality of the excavated section ranges from very good to highly precarious

In the case that the final lining is not conceived to have structural character or provide structural func-tion, but to provide a “cosmetic” function only, including the case in which this element should miss completely such as it happens in some designs, then, it will be the primary phase support that will have to fulfil all structural functions formerly assigned to the final lining, both in terms of structural capacity as well as in terms of structural reliability.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

In a certain sense, something similar happens also in the case of the pre-cast concrete ring segments applied to cover tunnels excavated through TBM, because of the fact that this single support shall fulfil all permanent static functions. Moreover, in this case, each element composing the lining shall fulfil as well all highly demanding temporary structural functions, which are related to the construc-tion process, to the storing, handling, assembling processes, and, sometimes, to the process of counteracting forces exerted at the face by the TBM during excavation.

Finally, and independently from which is the case, the structural design shall begin from the defini-tion of acting loads and of boundary conditions. As such, the geomechanical characterisation of the environment to be excavated results being a fundamental prerequisite.

Geomechanical characterisation of rocks and ground.

The identification of grounds, soils, rocks and rock mass, which will be impacted by the excavation, is the first step in the complex process of designing a tunnel. This characterisation is directly related to results of what is traditionally named a geological study, or a geological survey, or, more simply, the geology of the site of the underground construction work.

It is important that such identification and eventual classification of the involved soils, rocks and rock mass, is carried out not just following geologic criteria, but also following engineering criteria, in what is meant considering at any time physical and mechanical conditions and properties of the materials and of the system as a whole.

Since the tunnel will be definitely excavated and constructed in the rock mass on a natural scale, this will be in the end the medium towards which the geomechanical characterisation will be directed. Nonetheless, as a consequence, characterisation will pass from the characterisation of single materi-als (soils and intact rock) forming the rock mass, to the characterisation of structures (discontinuities) interconnecting materials composing the rock mass.

For highly pronounced rocky environments, in function of the fracture density and orientation (level of anisotropy) with respect to the rock medium, the rock mass can be represented with a continuum model, a discontinuum model, or an equivalent continuum model. For environments typically consisting of cohesive or incoherent soils, it will be generally referred to the respective continuum models.

In case a discontinuum model is applied, fundamental objective of the characterisation is to identify geometric and strength characteristics of discontinuities, thereby utilizing, as an example, Barton’s criterion, which becomes explicit through the following equation for shear stress:

Where:

t - shear stress

sn - normalized stress

fb - base friction angle (obtained through shear tests onto smooth, non-altered, surfaces)

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JRC = roughness coefficient (Joint Roughness Coefficient)

JCS = compressive strength of the discontinuity (Joint Compressive Strength).

In case rock mass can be represented by a continuum model or an equivalent continuum model, ac-

cording to the methodology proposed by Hoek and Brown (1997), in order to estimate geomechani-

cal parameters such as strength and deformation of the rock mass, which can be macroscopically

considered isotropic related to the specific scale of application, the following thee basic parameters

should be know, whereby two of them are related to the rock materials forming the rock mass, and

the third is related to the macro-structure of the rock mass:

- The uniaxial compressive strength of intact rock ¨sci¨

- The constant ¨mi¨ defining the friction character of the rock

- The Geological Strength Index ¨GSI¨ of the rock mass.

Two tables summarizing values to be possibly assumed by each of the first two parameters mentioned

above are enclosed. These tables can be used, as a first approximation, to estimate values which those

two parameters could assume for a specified rock, if laboratory tests are completely missing, or to

be used as complement to laboratory test results. Subsequently, Hoek’s tables to be applied for the

definition and determination of the third parameter, the GSI, are enclosed as well.

The following step consists in considering the geomechanical characteristics of strength and defor-

mation of the rock mass:

- The angle of friction of the rock mass ¨ϕm¨

- The cohesion of the rock mass ¨cm¨

- The uniaxial compressive strength of the rock mass ¨scm

¨

- The modulus of deformation of the rock mass ¨Em¨.

The following empirical equations are recommended by Hoek and Brown:

ϕm = sen-1[(6am

b(s+ m

b s

3n)a-1)/(2(1+ a)(2+ a)+ 6am

b(s+ m

b s

3n)a-1)]

cm

= sci[(1+2a)s+(1-a)m

b s

3n](s+ m

b s

3n)a-1/(1+a)(2+a)[1+(6am

b(s+m

b s

3n)a-1)/((1+a)(2+a)]0.5

scm

= sci [(m

b+4s–a(m

b–8s))*(m

b/4+s)a-1]/[2(1+a)(2+a)]

Em = 1000(s

ci/100)1/2 10 (GSI-10) / 40 (in MPa)

Where:

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

s3n

= s3max

/sci

(s3max

/scm

) = 0.47.(scm

/γ.H)-0.91

with H = depth of the tunnel and ¨D¨ construction disturbance factor: equal to ¨0¨ for undisturbed

conditions and equal to ¨1¨ for not well controlled explosions.

It must be highlighted that since these equations are empirical, they should be used carefully. And

in any case, it is recommended that each of those seven geomechanical parameters is quantified in

statistic terms, thus assigning to each of them a probabilistic distribution in function of its nature,

and some statistic indexes and factors in function of the specific knowledge available for them.

Examples

Fresh basalt, chert, diabase, gneiss,granite, quartzite.

Limestone, marble, sandstone,schist.

Concrete, phyllite, schist, siltstone.

Chalk, claystone, potash, marl,siltstone, shale, rocksalt.

Grade*

R6

R4

R3

R2

R0

Term

Extremelystrong

Very strong

Strong

Mediumstrong

Weak

Very weak

Extremelyweak

Pointloadindex(MPa)

> 10

2 - 4

1 - 2

**

**

Field estimate of strength

Specimen can only be chipped with ageological hammer.

Specimen requires more than one blowof a geological hammer to fracture it.

Cannot be scraped or peeled with apocket knife, specimen can befractured with a single blow from ageological hammer.

Can be peeled with a pocket knife withdifficulty, shallow indentation made byfirm blow with point of a geologicalhammer.

Indented by thumbnail. Stiff fault gouge.

* Grade according to Brown (1981).** Point load tests on rock with a uniaxial compressive strength below 25 MPa are likely to yield highly ambiguous results.

> 250

Amphibolite, sandstone, basalt,gabbro, gneiss, granodior i te,peridotite, rhyolite, tuff.

R5 4 - 10 Specimen requires many blows of ageological hammer to fracture it.100 - 250

50 - 100

25 - 50

5 - 25

Highly weathered or altered rock,shale.R1 **

Crumbles under firm blows with point ofa geological hammer, can be peeled bya pocket knife.

1 - 5

0.25 - 1

Uniaxialcomp.strength(MPa)

Table 5.1 - Rock bulk degrees in accordance with the estimates of resistance the uniaxial compression for different types of rock.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Values of the constant Mi for intact rock group. Note that values in parenthesis are estimates. The

range of values quoted for each material depends upon the granularity and interlocking of the crystal structure - the higer values being associet with tightly interlocked and more frictional characteris-tics.

* These values if relate the proven samples of unbroken rock in the normal direction to the stratification. The gotten value of mi it can vary significantly if the rupture itself verifies in the direction of the weak or plain plan of stratification.

1* Note: this table contains substantial exchanges in reference to the shown ones in preceding publications. Such exchanges had been made to reflect given accumulated in recent tests of laboratory and the gotten experience of great quarrels techniques with Geologists and Engineers geologists.

Rocktype

TextureCoarse Medium Fine Very fine

Clastic

Conglomerates(21 3)+

Sandstones17 4+

Siltstones7 2+

Claystones4 2+

Crystallinelimestone(12 3)+

Spariticlimestones( 10 2 )+

Micriticlimestones(9 2)+

Dolomites(9 3)+

Gypsum( 8 2 )+

Anhydrite( 12 2 )+

Chalk07 2+

SEDIMENTARY

METAMO

RPHIC

IGNEOUS

Non foliated

Slightly foliated

Foliated*

Marble9 3+

Hornfels( 19 4 )+

Metasandstone( 19 3 )+

Quartzites20 3+

Migmatite(29 3)+

Amphibolites26 6+

Gneiss28 5+

Schists12 3+

Phyllites(7 3)+

Slates7 4+

Granite32 3+

Diorite25 5+

Granodiorite(29 3)+

Cabbro27 3+

Dolerite(16 5)+

Norite20 5+

Hypabyssal Porphyries(20 5)+

Diabase(15 5)+

Peridotite(25 5)+

Class

Non-Clastic

Plutonic

Vulcânica

Gr upo

Carbonates

Evaporites

Organic

Light

Dark

Lava

Pyroclastic

Rhyolite(25 5)+Andesite25 5+

Dacite(25 3)+Basalt(25 5)+

Obsidian(19 3)+

Agglomerate(19 3)+

Breccia(19 5)+

Tuff(13 5)+

Breccias(19 5)+

Greywackes(18 3)+

Shales(6 2)+Marls(7 2)+

Table 5.2 - Values of mi for different classifications of rock according to its geomorfológical origin.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.3 - Classroom determination of rock according to GSI.

Table 5.4 - Values of the GSI in function of the condition of the rock in the surface and its breaking.

STRUCTURE

BLOCKY - Well interlocked un-disturbed rockmass consisting of cubical blocks formed bythree intersecting discontinuity sets.

INTACT OR MASSIVE - Intact rock specimensor massive in situ rock with a few widely spaceddiscontinuities.

VERYBLOCKY - Interlocked, partially disturbedmass with multi-faceted angular blocks formedby 4 ormore joint sets.

BLOCKY/DISTURBED/SEAMY - Folded withangular blocks formed by many intersectingdiscontinuity sets. Persistence of beddingplanes or schistosity.

DISINTEGRATED - Poorly interlocked, heavilybroken rock mass with mixture of angular androunded rock pieces.

LAMINATED/SHEARED - Lack of blockinessdue to close spacing of weak schistosity orshear planes.

90

80

70

60

50

40

30

20

10

N/A N/A

N/A N/A

DECREASING SURFACE QUALITY

Rock type:

GSI s :election

SURFACE CONDITIONS

VERYGOOD GOOD FAIR POOR VERY

POOR

General

31

DECR

EASIN

G INT

ERLO

CKING

OFRO

CKPIE

CES

SURFACE CONDITIONS OF DISCONTINUITIES

VERYGOOD GOOD FAIR POOR VERY

POOR

A- Thick bedded, very blocky sandstoneThe effect of pelitic coatings on the bedding planes isminimized by the confinement of the rock mass. In shallowtunnels or slopes these bedding planesmay cause structuralycontrolled instability.

B - Sand-stone withthin inter-layers ofsiltstone

70

60

50

40

30

20

10

C - Sand-stone andsiltstone insimilaramounts

D - Siltstoneor silty

shale withsandstonelayers

E - Weaksitstone orclayey shale

withsandstonelayers

F - Tectonically deformed, intensivelyfolded/faulted, sheared clayey shale orsiltstone with broken and deformedsandstone layers forming an almostchaotic structure

C, D, E and G - May be more or less foldedthan illustrated but this does not change thestrength. Tectonic deformation, faulting andloss of continuity moves these categories to FandH

G - Undisturbed silty or clayeyshale with or without a few verythin sandstone layers

H - Tectonically deformed silty or clayeyshale forming a chaotic structure withpockets of clay. Thin layers ofsandstone are transformed into smallrock pieces

Means deformation after tectonic disturbance

COMPOSITION AND STRUCTURE

Rock type: Flysch GSI Selection: 31

A

B C D E

F

G H

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Table 5.5 - GSI determination in function of the superficial quality observed and its degree and breaking.

Type of behaviour and pre-selection of the initial support.

The geostatic behaviour of an underground excavation, or more schematically, the “type of behaviour of the excavation”, depends from the combination of a number of factors, which can be identified, in highly simplified terms, as: the state of pre-existing natural stresses in the environment where the excavation will take place, and its geomechanical strength.

From the description of the structure and the conditions of the surfaceof the rock mass, to select the appropriate interval of this table.Esteem the average value of Geolocical Strength Index (GSI) of thisinterval. It does not have very to be looked for to be necessary. Tochoose an acceptable value of GSI between 36 e 42 that to fix aGSI =36. It is also important to recognize that the criterion of Hoek-Brownwill have only to be applied in rock bulks where the dimension of thefragmented blocks is small making a comparison with the dimensionof the hollowing that must be evaluated. When the dimension of theindividual blocks is approximatively bigger to the quarter of thedimension of the excavation, generally the rupture would becontrolled for the structure and the criterion of Hosk-Brown would nothave to be used.

GEOLOGICAL STRENGTH INDEX

STRUCTURE

SURF

ACECO

NDITION

UNBROKEN OR MASSIVE - unbroken rocks ormassives rocks with few widely separatediscontinuities

BROKEN - Massive rock partially disturbed,formed in cubic blocks formed for three ortogonaissystems of discontinuity, very joined well betweenitself.

MUCH BROKEN - Massive rocky partiallydisturbed, formed in blocks joined between itself,formed for fourmore the systemsof discontinuity.

BROKEN/DISTURBED - Massive rock foldedand/or failed with angular blocks formed by theintersection of the somesystemsof discontinuity.

DISINTEGRATED - Massive rock highly brokenwith mixtures of angular and rounded off, joinedfragmentos poor between itself.

STRATIFIED/LAMINATED - Rock tectonicstratified and fissured. The schists prevail on anysystemof discontinuity, completelywithout blocks.

Decreasin

ginterlo

ckingofrock

pieces

90

80

70

60

50

40

30

20

10

N/A N/A

N/A N/A

Reduction of the surface quality

VERY

GOOD

Very

wring

led,surfac

eswitho

utme

teoriz

ation

.

GOOD

Wrin

gled,

sligh

tlyme

teoriz

ed,spo

ttedo

xides

urfac

es.

MEDIA

Plain

,mod

erate

lyme

teoriz

ed,m

odifie

dsurfac

es.

BAD

Mirro

rsof

brea

king,

surfa

cesve

ryme

teoriz

edwith

hard

wadd

ingso

fang

ularfr

agme

ntos.

VERY

BAD

Mirro

rsof

brea

king,

surfa

cesve

ryme

teoriz

edwith

hard

clayw

addin

gs.

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In a first approximation (and in case additional elements such as on-site measurements are missing), the state of natural stress can be related directly to the depth or covering of the excavation (H) and to the geomechanics of the environment where the excavation will take place. Moreover, it can be related, with some approximation, to the strength of materials dominating the environment on the one side, and to the geomechanical macro-structure of the rock mass on the other side (fractures, modifications, anisotropies and morphologies of surfaces from discontinuities, between others), for whose identification several geomechanical quality indexes can be used (such as e.g. the RMR of Bieniawsky, the Q of Barton, the RSR of Wikham, etc.), and especially the already commented Hoek’s GSI.

If natural stresses result being considerably high with respect to the strength of the rock mass, and simplifying further, one can directly refer to the non-confined compressive strength of the rock mass (s

cm). The latter can be directly related to the state of natural stress (γ.H), with (γ) being the density

of the rock mass, whereby, for such correlation, the important concept of “index of excavation com-petence” (IC=s

cm/γ.H) is introduced, which will be very useful at the time of discriminating the type

of behaviour of the excavation in the above described circumstances. Whereas, for high values of the above mentioned index (IC), such as it generally happens for moderate coverings, where natural stress conditions result being low as well, the geomechanical quality of the rock mass (GSI) alone will be sufficiently conditioning and discriminating of the type of behaviour, as it will be explained forward.

Within this framework, for practical reasons, the possible types of behaviour of an excavation can be summarized in the following five ones:

*TYPE OF BEHAVIOUR “A”

Behaviour presenting stable overhead face and cavity. This type of behaviour appears when the state of stress at the cavity face and the surrounding, forming as a consequence of the redistribution of natural stresses following excavation, is such that stresses in the environment are not overcoming strength characteristics of the environment itself. Thus, the relationship of mobilization between strength and stresses is always greater than one (FS>2.5).

The deformation phenomena, which follow the excavation, evolve by maintaining themselves in the elastic range; they are immediate and generally of modest capacity, thereby limiting themselves to the order of few centimetres. The nucleus’ axial deformations, which appear in the form of extru-sions, are negligible.

The free radial deformation of the cavity (percentage relation between radial displacement and radius of the tunnel: R

o) is very low (e<1%). Even lower is the radial deformation at the face (e

o<<0.5%). The

plastification (expressed as the spread of plastic radius, Rp) is practically inexistent (R

p/R

o=1), and the

index of excavation competence results being very high (IC>>0.45). The GSI, which is the principal control over the behaviour of the when coverings are contained, is high (GSI>60).

The eventual presence of water, also if hydrodynamic conditions exist, does generally not influence the stability of the tunnel, unless for loose ground, or unless excessively high hydraulic gradients cause such a wash-out that shear strength along the existing planes of discontinuities is drastically reduced.

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The whole excavation is globally stable. Eventually, only extremely localized instabilities might occur in the form of isolated blocks falling down, due to localized unfavourable geo-structural conditions within discontinuous rock mass.

Stabilizing interventions are generally the lowest and are principally directed towards avoiding the occurrence of localized sliding of ground, which could be potentially dangerous for people, and, at the same time, towards maintaining a regular excavation profile.

Regarding specifically the support to be pre-selected for this class, the installation of isolated spiles is deemed to be sufficient. Eventually, a thin layer or fiber-reinforced shotcrete may be applied as well.

Photo 5.6 - Example of excavation in area of type A behaviour.

*TYPE OF BEHAVIOUR “B”

Behaviour presenting stable overhead face and stable cavity in the short term. This type of behaviour appears when the state of stress at the cavity face and the surrounding, forming as a consequence of the redistribution of natural stresses following excavation, is such that stresses in the environment approach elastic strength characteristics of the environment itself. Thus, the relationship of mobiliza-tion between strength and stresses is greater than one (FS

f≈2) at the face and is near to one (FS

c≈1)

in the cavity surrounding at a certain distance from the prior one.

The deformation phenomena, which follow the excavation, evolve in the elastoplastic range in the cavity surrounding; they are slightly postponed in time and generally of modest capacity, in the order of few centimetres. The nucleus’ axial deformations, which appear in the form of extrusions, are limited and do not influence the stability of the tunnel since the ground is still capable to mobilize sufficient residual strength.

In case of high coverings, the free radial deformation of the cavity corresponds to (1%<e<2.5%). The radial deformation at the face corresponds to (e

o<0.5%). The plastification radius corresponds

to (1<Rp/R

o<2), and the index of excavation competence corresponds to (0.3<IC<0.45). The GSI,

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which is the principal control over the behaviour of the excavation when coverings are contained, is relatively high (40<GSI<60).

The eventual presence of water, and particularly if hydrodynamic conditions exist, promotes expand-ing of plastification by reducing the ground’s shear strength capacity, thereby increasing the relative importance of instability phenomena. As a result, the presence of water must be prevented, especially at the excavation advancement face, by draining water in order to keep it as far as possible towards the nucleus’ outer side.

Instability phenomena, appearing in the form of localized sliding at the face and the surrounding of the cavity, leave generally the time to take action after a relatively short dismissal from the working front, allowing the use of traditional radial containment intervention methods.

Stabilizing interventions are generally of conservative type and are based on passive contrast techniques, which are directed towards avoiding complete confining of the rock mass in the cavity surrounding and thus its decompression well beyond the surrounding itself.

Regarding specifically the support to be pre-selected for this class, the installation of a system com-posed of the integration of a layer of fiber-reinforced shotcrete of moderate thickness with short spiles, and eventually light metal centres, capable to contrast radial loads with an appropriate safety factor, is considered appropriate.

Photo 5.7 - Example of excavation in area of type B behaviour.

*TYPE OF BEHAVIOUR “C”

Behaviour presenting unstable cavity. This type of behaviour appears when the state of stress at the cavity face and the surrounding, forming as a consequence of the redistribution of natural stresses following excavation, is such that stresses in the environment slightly overcome elastic strength characteristics of the environment itself. Thus, the relationship of mobilization between strength and

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stresses is near to one (FSf≈1) at the face and is lower than one (FS

c<1) in the cavity surrounding at

a certain distance from the prior one.

Deformations develop slowly with respect to normal excavation advancement velocities, and, although evident collapses of the overhead face do not take place because of the moderate tension unbalance, the nucleus’ axial deformations, which appear in the form of extrusions, may influence the stability of the tunnel. Moreover, due to the occurrence of plastic deformations already at the face itself, the cavity conditions far from the face result rather critical, and the plastic fringe develops radially with an extension which overcomes the tunnel radius, thus resulting in a considerable radial convergence and axial deformations at the front.

In case of high coverings, the free radial deformation of the cavity corresponds to (2.5%<e<5% The radial deformation at the face corresponds to (0.5<e

o<1%). The plastification radius corresponds to

(2<Rp/R

o<4), and the index of excavation competence corresponds to (0.2<IC<0.3). The GSI, which

is the principal control over the behaviour of the excavation when coverings are contained, is low (30<GSI<50).

The eventual presence of water promotes expanding of plastification by reducing the ground’s shear strength capacity, thereby increasing the relative importance of instability phenomena. As a result, the presence of water must be prevented, especially at the excavation advancement face, by draining water in order to keep it as far as possible towards the nucleus’ outer side.

Regarding specifically the support to be pre-selected for this class, stabilization actions are generally realized in that only an adequate counteracting structure is applied, which consists of ribs and fiber-reinforced shotcrete, having sufficient weight to withstand equilibrium loads. Just eventually, the structure may be complemented by scaffolding the overhead face with glassfiber composite elements, which are placed up to a distance of the same dimension order of the tunnel radius, with the objec-tive of providing to the overhead face enough stiffness so as to enable the temporary equilibrium of the cavity. These elements’ function will end as soon as the installation of the primary support will begin, after a limited, thus beneficial, convergence of the cavity will have taken place.

Though, due to the more critical conditions characterizing this class, interventions may become mainly of improving character. For this purpose, the consolidation of the face by means of glassfiber composite elements may be extended to the vicinity of the excavation perimeter, by installing a set of outlying glassfiber composite elements. These will be slightly sloping with respect to the tunnel axis so as to interfere with the mechanical action of the pre-consolidating scaffolding, a rock crown immediately outside the excavation perimeter, thus contributing to limit the extension of the plasti-fication radius of the rock around the excavation, and, as a result, limit final equilibrium loads above the selected support.

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Photo 5.8 - Example of excavation in area of type C behaviour.

*TYPE OF BEHAVIOUR “D”

Behaviour presenting unstable overhead face. This type of behaviour appears when the state of stress at the cavity face and the surrounding, forming as a consequence of the redistribution of natural stresses following excavation, is such that stresses in the environment overcome strength character-istics of the environment itself. Thus, the relationship of mobilization between strength and stresses is lower than one (FS

f≈<1) at the face and is much lower than one (FS

c<<1) in the cavity surrounding

at a certain distance from the prior one.

Deformation phenomena are unacceptable as they evolve rapidly in the braking range, thus giving rise to serious instabilities’ displays such as breakouts at the face and collapses of the cavity, which do not leave the time to take action through radial containment interventions. As such, the nucleus’ axial deformations, which appear in the form of extrusions or collapses, influence the stability of the tunnel. At the face the tension unbalance is such that it gives rise to high deformation gradients, because the face’ stability conditions result critical for normal excavation advancement velocities. Moreover, the cavity conditions far from the face result critical, and the plastic fringe develops radially with an extension which overcomes the tunnel radius, thus resulting in a highly important radial convergence. As a result, pre-consolidating interventions must be provided upstream of the excavation advancement face in order to put in place pre-containment actions capable to induce artificially arc effects.

In case of high coverings, the free radial deformation of the cavity corresponds to (5%<e<10%). The radial deformation at the face corresponds to (e

o>1%). The plastification radius corresponds to

(Rp/R

o>4), and the index of excavation competence corresponds to (0.15<IC<0.2). The GSI, which

is the principal control over the behaviour of the excavation when coverings are contained, is low (20<GSI<40).

The eventual presence of water, if hydrostatic conditions exist, reduces even more the ground’s shear strength capacity, thus promoting a further increase of plastification and increasing the magnitude of deformation phenomena. If hydrodynamic conditions exist, water produces materials dragging

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Photo 5.9 - Example of excavation in area of type D behaviour.

phenomena and siphoning phenomena, which are absolutely unacceptable and dangerous for the global stability of the excavation. As a result, the presence of water must be prevented, especially at the excavation advancement face, by draining water in order to keep it as far as possible towards the nucleus’ outer side.

In order to contain the development of plastification, both beyond the overhead face and in the radial direction, a massive intervention of improving character directed towards the preventive consolida-tion of the nucleus by means of resistant glassfiber composite elements connected to the rock mass through the injection of cement mixes is very useful.

The pre-selected primary support must be heavy and should be constituted by a thick fiber-reinforced shotcrete layer and heavy metal ribs eventually integrated with radial elements to be applied for the improvement of the rock mass, whose number and length will depend essentially from the deforma-tion behaviour of the rock mass around the excavation. Such radial improving elements may be made of glassfiber composite, or they may be constituted by structurally equivalent strands or spiles. This will depend from the practical feasibility related to construction with respect to the number and the length which will result necessary.

*TYPE OF BEHAVIOUR “E”

Unstable behaviour. This type of behaviour appears when the state of stress at the cavity face and the surrounding, forming as a consequence of the redistribution of natural stresses following excavation, is such that stresses in the environment highly overcome strength characteristics of the environment itself. Thus, the relationship of mobilization between strength and stresses is much lower than one (FS<<1) both at the front and in the cavity surrounding.

This type of behaviour is characterised by a short-term instability of the front with immediate sliding breakouts of the face itself as a result of advancement operations and by the presence of a highly emphasized free convergence of the cavity.

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Such behaviour is typical e.g. of incoherent grounds, of cataclastic rock mass, as well as in fault zones, or in the presence of high hydraulic gradients, or in any case whereby extremely high tension unbalances determine immediate sliding of the face just as the cavity is opened.

In the case of crossing faults, or in any tract characterised by a short-term instability of the face with immediate collapse conditions, the necessity of pre-confining, pre-support or improvement inter-ventions, or eventually of an adequate combination of the aforesaid methods, to be applied during excavation advancement should be evaluated in function of geo-structural and hydrogeological characteristics.

In case of high coverings, the free radial deformation of the cavity corresponds to (e>10%). The radial deformation at the face corresponds to (eo >>1%). The plastification radius corresponds to (R

p/R

o>>4),

and the index of excavation competence corresponds to (IC<0.15). The GSI, which is the principal control over the behaviour of the excavation when coverings are contained, is very low (GSI<20).

The eventual presence of water reduces drastically the ground’s shear strength capacity, thus promot-ing a greater extension of plastification and increasing the magnitude of deformation phenomena, thereby possibly producing materials dragging phenomena and siphoning phenomena, which are absolutely unacceptable and dangerous for the global stability of the excavation. As a result, the presence of water must be prevented by draining water in order to keep it as far as possible towards the outside.

Due to the reduced load capacity of soils, besides resulting sufficiently heavy and properly integrated such as for the prior type, the primary phase counteracting system should foresee as well adequate complementary technical solutions (such as e.g. ribs with incremented support, remedial treatments of the centres’ foundation ground, temporary inverted archs, permanent inverted archs during the advancement of works, excavation’s pre-supporting archs, etc.).

The pre-selected primary support must be extremely heavy and should be constituted by a extremely thick fiber-reinforced shotcrete layer and heavy metal ribs integrated with radial elements to be densely applied for the improvement of the soil. Such radial improving elements may be made of glassfiber composite, or they may be constituted by structurally equivalent strands or spiles. This will depend from the practical feasibility related to construction with respect to the number and the length which will result necessary.

Photo 5.10 - Example of excavation in area of type E behaviour. Figure 5.1 - Example of conceptual representation of support for type E soils.

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Table 5.6 - Classification of support behavior in function the GSI, index of competence and quality of the bulk and the covering of the escavation.

TYPE BEHAVIOURCOVERING

HIGHIC

LOWGSI

PRESELECTION OF THE SUPPORT(Tunnel of approx. 10 m diameter)

C 0.2 - 0.3

Sprayed concrete (15-20 cm)

+ Spiles (L = 6 m) (density 0.5/m²)or Medium ribs @ 1 m

+ Reinforcement of the face (eventual)

D 0.15 - 0.2

Instable faceInstable cavity(high deformations)

FS 1f

5% < <10%(2 < R /R < 4)p o

FS > 1c

<1%o

Sprayed concrete (20-25 cm)

+ Heavy ribs @ 1 mor spiles (L = 6-9 m)(density 1/m²)

+ Reinforcement of the face and extrados

+ Integrative spiles (eventual)

E

Generalized instability(very poor rock massand/or fault zone)

FS << 1f

> 10%(R /R >> 4)p o

FS << 1c

>> 1%o

< 0.15

A

Stability at the faceStability in the cavityEventual instabilities(blocks' kinematisms)FS > 2.5f

< 1%(R /R = 1)p o

FS > 2.5c

o<<0.5%

> 0.45Sprayed concrete (5-10 cm)

+ Spiles L = 4 m (eventual)> 60

B 0.3 - 0.45

Sprayed concrete (10-15 cm)

+ Spiles (L= 4-6 m)(density 0.25/m²)or light ribs @ 1.5 m

Stability at the faceInstable cavity

FS 2,5f

1%<(1<R /R < 2)p o

FS 1c

o<0.5%<2.5%

40 - 60

30 - 50

20 - 40

< 20

Sprayed concrete (20-30 cm)

+ Very heavy ribs @ 1 m

+ Reinforcement of the face and extrados

+ Integrative spiles

+ Pre-support (eventual)

Face approaching equilibriumInstable cavity

FS 1f

2.5% < <5%(2 < R /R < 4)p o

FS > 1c

0.5%< <1%o

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Determination of applied loads.

Once the support, necessary for an adequate stabilization of the tunnel, has been pre-selected, and considering the determination of the type of behaviour of the excavation, according to rules defined before, as base, in order to proceed in elaborating a detailed structural design, all related analyses and calculations must be conducted stepwise. The fundamental objective of such analyses and calculations is the determination of loads acting over the support structure, besides, obviously, the calibration of the rigidity of the soils which will hold the same structure of the support to be designed.

In order to proceed to the practical determination of applied loads, it is convenient to differentiate the excavated sections of the tunnel corresponding to modest coverings (up to the order of 10 times the width ¨b¨ of the tunnel) from the deeper excavated sections, given the fact that those applied loads depend from such covering (H) conditions. Applied loads are then generally estimated by ap-plying two different methodologies for the two cases: the methodology of the “loads’ solid” in the first case, and the one of the “characteristic lines” in the second case.

Moreover, different schemes are applied as well for the acting loads’ distribution: over the final lining this is vertical gravitational loads in the vault and horizontal loads in the frontispieces for sections with moderate coverings, and radial loads only in the vault for deeper sections. Over the primary support, the model of radial loads in the vault and in the frontispieces is generally applied indiscriminately.

For excavated sections below modest coverings, and classifiable as “superficial” (H<2b), the contrast-ing equilibrium load over the primary support and the vertical loads acting over the final lining will be the same, and will be also equal to gravitational loads (γ.H) corresponding to a solid of the same height of the specific covering.

Over the final lining of these sections, design horizontal loads will be the same as loads derived from the application of the classical theory of thrusts over soils containment structures, whereby seismic actions will contribute additionally.

For excavated sections below modest coverings, and classifiable as “moderate” (2b<H<=10b), the contrasting equilibrium load acting over the primary support will be radial and will be equal to the gravitational load corresponding to a solid of height Hp

=a.(b+h), where ¨a is a coefficient of linear proportion (Terzaghi’s coefficient) that is function of the geomechanical characteristics of the ground, and ¨h¨ Is the height of the tunnel section.

The linear proportion coefficient (a) is function of the ¨GSI¨ and of ¨mi¨, as it can be observed in the graph attached, and can be derived approximately through the following equation:

a = 1244 mi-1.433.GSI (0.0004.mi2-0.0046.mi-1.2344)

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TERZAGHI'S LOAD FACTOR “ALPHA” (Perri, 2000)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

3.0

3.2

3.4

3.6

3.8

4.0

0 10 20 30 40 50 60 70 80 90 100

GSI

mi = 10

mi = 13

mi = 16

mi = 20

mi = 30

mi = 25

mi = 35

mi = 5mi = 7

= 1244mi GSI–1,433 (mi0,0004mi–0.0046mi–1.2344)

Graphic 5.1 - Terzaghi’s load factor “alpha” (Perri, 2000).

In those sections classified as intermediate, in order to estimate vertical loads acting over the final lin-ing, an appropriate reduction of the factor ¨a¨, between 25% and 50% of the value derived through the equation, could be eventually considered. This would depend from the geomechanical conditions and from the construction times foreseen for the lining.

Graphic 5.2 - Relationship between loads acting in to the supports vs. covering, incidence of the factor Alfa in function of the GSI.

SUPERFICIAL SECTIONS INTERMEDIATE SECTIONS DEEP SECTIONS

LOAD SOLID CHARACTERISTIC LINES

D = YHv D = Ya(b+h)v D = Ppplv

b(GSI/5)

b(75/GSI)

HI Hs

b

h

LOADS ABOVE OF THE ARC VS. COVERING (H)AND TYPE OF ROCKS (GSI)

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The above mentioned reduction of the design load acting over the lining would be in fact the more emphasized, the more it can be assumed that the primary support has been effectively loaded by the effects of the loads’ solid before the construction of the lining. Thus, the latter should only hold the whole portion of loads not already taken over by the primary support due to the effects of the loads’ solid before the construction of the lining.

Over the final lining of these intermediate sections, design horizontal loads will be the same as loads derived from the application of the classical theory of thrusts over soils containment structures, or they will be simply the same as loads deriving from the elastic reaction to confining generated by the soil over the deformable lining, following what is indicated by the analysis model applied in each specific case.

Seismic actions will be only considered where explicitly recommended by geologic and geotechnical studies.

For sections classifiable as “deep” (H>10b), the contrasting equilibrium loads acting over the primary support will be the ones derived through an interaction analysis following the characteristic lines method.

Over the final lining, design horizontal loads will be radial and will be only applied in the area of the vault. Their value will be proportional to the extension of the plastification radius obtained at the equilibrium reached by the application of the primary support, or, eventually, of the radius which can be actually reached up to the actual entrance into action of the lining, while applied horizontal loads will be resulting from the elastic reaction to confining generated by the soil over the deform-able lining.

Seismic actions will be only considered where explicitly recommended by geologic and geotechnical studies.

All the afore mentioned elements, related to criteria to be used to calculate loads acting over sup-ports, can be accurately applied to obtain a detailed structural design on the base of the structural capacity of specific supports to be possibly applied in each specific case.

These same elements have been used in this handbook to define supports to be applied on the base of most common geomechanical conditions, and considering generally available supports, as it will be reported in the following chapters.

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Sprayedconcreteespessurae = 0.14

Spiles2 IPN-140

Centres

R5.54

R 4.37

10º

TDR

7.99

1.76

1.83

0.71

Figure 5.2 - Primary support - loading scheme.

R min

7.39

6

CB = Loads in the vault CH = Loads in the sides

1.09 1.09R 4.05

19º

1.8319º0.70

4.09 4.09

TDR

R 5.14CH CH

CB

Figure 5.3 - Loading scheme on the final lining - moderate coverings.

R min

7.39

6

CB = Loads in the vault CH = Loads in the sides

1.09 1.09R 4.05

19º

1.8319º0.70

4.09 4.09

TDR

R 5.14

CB

CHCH

Figure 5.4 - Loading scheme on the final lining - high coverings.

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5.3 - Design of supporting structures made of fiber-reinforced shotcrete.

In modern tunnels technology, supporting structures placed during the excavation are composed of a number of resistant elements, of which fiber-reinforced shotcrete, eventually complemented by metal ribs and spiles, is the principal element. The placement of ribs and spiles may occur, case by case, following different combinations. Examples are indicated in the following table for five typical primary supports (SP-a; SP-b; SP-c; SP-d; SP-e), which, in the specific case of the table, are referred to a tunnel of approximate width (b), or equivalent diameter, of 10 meters.

In the mentioned table, it can be observed that, with except for the two extreme situations cor-responding, in the one case, to geomechanical conditions for which it is not necessary to integrate the support with metal ribs, and in the other case, to geomechanical conditions for which their use is essential, in all other intermediate situations, which are more recurrent in tunnel practices, it is always possible to decide upon at least to alternative technical solutions for the support. One solu-tion is based on the use of metal ribs to integrate the shotcrete, while the other solution is based on a systematic and intensive use of metal spiles to integrate the shotcrete.

In fact, from a strictly structural point of view, it is certainly possible to reach the same result in what concerns the structural capacity or the contrasting capacity of the support, by using the two alternative technological solutions. Thus, finally, a practical selection depends anyway from other factors such as, for example: the availability of the elements on the construction site, the availability of equipment for the placement of those elements, compared costs for those elements on a specific market, contractual conditions, production efficiencies, the expertise and tradition of the constructor, and the workers’ safety.

Of course, a wider set of other technical-comparative advantages or disadvantages might be mentioned as well for the two alternative solutions, but the subjective judgement of the author would certainly strongly influence this aspect, and this would definitely invalidate all respective positions.

In order to highlight technical-economic advantages to which it is normally turned to when the alterna-tive solution of fiber-reinforced concrete must be sustained, without damaging however the objective proposal for other supporting solutions, we underline that this solution leads to qualitatively important technical improvements, which provide added value to the design, thus allowing to obtain:

- A homogeneous lining without cavities or voids which might be generated at the interface between the rock mass and the shotcrete with welded wire mesh.

- The reduction of rebound of material on the welded wire mesh.

- A more compact and even mix.

- An improvement in safety conditions of the construction site due to the reduction of the personnel’s exposure time to excavation operations. In fact, it is possible to begin stabilization of the working face immediately after explosions have taken place. In this way, it is avoided that personnel is exposed to the risk of eventual sliding of material remaining on the surface of the excavation, as it is the case for fastening operations of the welded wire mesh.

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- A homogeneously reinforced surface, capable to absorb stresses in its entire thickness.

- It generates a dúctil concrete capable to absorb efforts.

- Flexural-tension stress capacity.

- Capability to absorb energy through deformation.

Finally, on the base of the available, or the foreseen, supporting solutions alternatives for each design, it is necessary to proceed to a specific selection for each design section, by comparing values of pres-sures (loads) applied in function of the coverings and of the possible geomechanical conditions of the forward coming soils (whereby these are represented, for example, by Hoek’s Geological Strengh Index) with values of capacities (strengths) of the available supporting structures.

For example, following this procedure for a tunnel with approximate width and equivalent diameter of 10 meters, the supports indicated in the following table have been preliminarily obtained.

Type ofsupport

Fiber-reinforcedshotcrete

Metal ribs Capacity(Kg/cm²)

SP-a 1.5

2 IPN140 each 150 cm 2 x 4 m each two ribsSP-b

or, alternatively, 7 spiles x 4 @ 150 cm (without ribs)2.5

2 IPN160 each 125 cm 4 x 6 m each two ribsSP-c

or, alternatively, 11 spiles x 6 each 150 cm (without ribs)3.5

2 IPN200 each 100 cm 6 x 6 m each two ribs

or, alternatively, 15 spiles x 6 each 100 cm (without ribs)4.5

2 IPN200 each 075 cm 10 x 6 m each two ribs 6.5

Metal spiles 20 t

SP-e

SP-d

10 cm

14 cm

16 cm

20 cm

20 cm

- -

Table 5.7 - Geomechanical and structural characteristics of base supports.

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Alternatively, the design of a support made of fiber-reinforced shotcrete may be also realized on the base of the calculation of its residual flexural strength, with respect to a support made of shotcrete reinforced through welded wire mesh.

In fact, it is already since some decades that shotcrete has been traditionally applied universally in tunnels construction, thereby being coupled with a layer of metallic wire mesh with various objec-tives: providing a certain flexural strength to the concrete, controlling shrinkage cracking, improving adhesion to faces and heading of the excavation, and limiting rebound.

Thus, since the principal functions of the mesh result being much more efficiently performed by metal fibers, it is easy to understand how the replacement of the metallic wire mesh with metal fibers has taken rapid spread.

At the same time, it has been equally easy and obvious to turn to a calculation methodology, for supports made of fiber-reinforced shotcrete, that departed from researching mechanical equivalence between the pressure-flexural strength capacity of a layer of concrete reinforced through a metallic wire mesh installed in the middle of its thickness, and an equivalent layer of fiber-reinforced concrete.

The flexural strength (maximum resistant moment) of a 1 m concrete slab of thickness (d) reinforced by a metallic wire mesh of section S

m (mm2) and strength s

y’ (N/mm2), installed in the middle of its

thickness (d/2 in mm), can be obtained (in Nmm) through the equation:

Table 5.8 - Pre-selection of base supports in function of the GSI and of the covering.

Covering:Geomechanics

GSI <= 20

20 < < 40GSI

30 < < 50GSI

40 < < 60GSI

GSI > 60

H (m)

5 -10

H (m)

10-20

H (m)

20-100

H (m)

100-150

H (m)

150-200

H (m)

200-300

H (m)

300-500

SP-b SP-b SP-b SP-bSP-a

SP-b SP-a SP-a SP-aSP-a

SP-c SP-c

SP-c SP-c SP-c SP-dSP-c

SP-c SP-a

SP-e SP-eSP-e SP-e SP-e SP-eSP-e

SP-e SP-e

SP-d SP-d

SP-d SP-d SP-d SP-dSP-d

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while the maximum resistant moment of the same 1 m fiber-reinforced concrete slab results from:

where feq

is the equivalent tensile strength on bending of fiber-reinforced concrete in N/mm² (MPa), whereby, from the equivalence of the resistant moments, it is finally obtained:

feq

= 0.0027.Sm .s

y’/d (strength requested to achieve the equivalence given a specified thickness)

d = 0.0027.Sm .s

y’/f

eq (thickness requested to achieve the equivalence given a specified f

eq)

The characteristic equivalent tensile strength of the fiber-reinforced concrete feq

must be initially ob-tained directly from tests on the beam, or, if testing results are missing, it can be preliminarily derived by empirical correlation with the base concrete type (from which tensile strength at the first-crack point on bending of fiber-reinforced concrete f

If principally depends) and the type and dosage of

fibers (elements from which ductility of fiber-reinforced concrete depends, expressed through the indexes D

0 and D

1).

Accordingly to all what was mentioned before, the structural design of supporting structures is based on the equivalence between flexural strength of shotcrete reinforced through metallic wire mesh (for example: 4 x 100 x 100 mm) and flexural strength of fiber-reinforced shotcrete. Essentially, it consists of the determination of the fiber dosage (kg/m3), assuring to the fiber-reinforced concrete, for a specified concrete strength class and for a specified thickness, an equivalent tensile strength (f

eq)

that is capable to provide the same resistant moment as the one obtained through a corresponding section of concrete reinforced through welded wire mesh.

Thus, one should begin with determining the value of the reported minimum equivalent strength which should be achieved, for each of the foreseen primary supports, and then, one should use the correlation (referential or experimental) between the dosage of the selected fiber and the equivalent tensile strength on bending (f

eq) of the specifically foreseen shotcrete (for example: C24/30).

By applying the equations reported before, the following minimum strengths are obtained, for fiber-reinforced concrete, for each of the four primary supports, corresponding to the four concrete thicknesses examined (10 cm – 14 cm – 16 cm – 20 cm):

For concrete type C24/30, corresponding to a characteristic cylindrical strength f’c = 240 kg/cm2,

European EFNARC standards indicate a tensile strength at the first-crack point of fIf = 3.4 MPa and,

for Wirand FS3N fibers, whose characteristics are included as an example, the producer reports the following approximate correlation between minimum ductility and dosage:

10 cm (P-a)f = 1.40 (MPa)eq

14 cm (P-b) 20 cm (P-d/e)f = 1.00 (MPa)eq

16 cm (P-c)f = 0.88 (MPa)eq f = 0.70 (MPa)eq

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Thus, the following correlation, between dosage and minimum equivalent tensile strength on bend-ing, results for concrete type C24/30:

An Excel sheet, appositely developed to complete the described procedure, follows, which corresponds to the design of fiber-reinforced sections whose flexural strength is equivalent to strength of sections reinforced through welded wire mesh.

In the last row of the table, one can observe that recommended dosage is maintained at 25 kg/m3 as minimum value, with reference to standards indicating this value as the minimum value for structural concrete, independently from theoretical results of analyses conducted.

Table 5.9 - Mechanical comparative degree between reinforced sections with fibers and sections reinforced with conventional steel for the determination of the thicknesses in the primary covering.

Ductility (f /f )eq lf 50 % 40 % 30 % 25 % 20 %kg/m de FS33 33 26 23 21 20

1.70 1.36 1.02 0.85 0.68f (MPa)eq

kg/m Fs33 33 26 23 21 20

A) Calculation of the equivalent strenghtConcrete e=10cmMesh(4/100)

Fiber(0.75x30)

mmN/mmmmmmmmkg/mkg/mmmNmmNmmmm

N/mm

2

2

2

3

2

Thickness (h) of the shotcrete sectionTensile strenght of the welded meshDiameter of the welded meshSide of the welded meshArea (s) of the weldwd mesh in the section of 1 meter of baseWeight of mesh/mWeight of mesh/mUseful thickness (d) of the section of concrete with meshFlexion resistant moment of the concrete withmeshFlexion resistant moment of the concrete with fibersThickness (h) of the section of concrete without fibersEquivalent strenght requested of the concrete with fibers

2

3

feq

1004144100125.71.9719.750

2,341,1152,341,1151001.40

Concrete e=14cmMesh(4/100)

Fiber(0.75x30)

1404144100125.719.714.170

3,277,5613,277,5611401.00

Concrete e=20cmMesh(4/100)

Fiber(0.75x30)

2004144100125.71.979.9100

4,682,230

B) Experimental determination of the fibers dosage

N/mm

%kg/m%

2

3

N/mm

kg/m

2

3

Minimum equivalent strenght fm requestedTheoretical flexion resistance of the concrete base (C24/30)Minimum requested ductility for concrete with fibersEmpirical reference dosage vs. requested ductilityRebond only of fibersRecommended dosage

fr

1.40

30

3.40412710

1.40

30

3.40412710

1.40

30

3.40412710

1.40

30

3.40412710

Concrete e=16cmMesh(4/100)

Fiber(0.75x30)

1604144100125.719.712.380

3,745,7843,745,7841600.88

4,682,2302000.70

Mesh(4/100)

Fiber(0.75x30)

Mesh(4/100)

Fiber(0.75x30)

Mesh(4/100)

Fiber(0.75x30)

Mesh(4/100)

Fiber(0.75x30)

Concrete e=10cm Concrete e=14cm Concrete e=20cmConcrete e=16cm

What has been reported is certainly a simplified way to proceed in sizing a resistant section made of SFRS to be applied as support for tunnels. The objective is essentially to define the section having the same flexural strength as the strength of an equivalent section reinforced through welded wire mesh. Nevertheless, it may be eventually useful whether it is the case to take a decision towards a change in the construction technology, thus whether to decide for the use of fiber-reinforced concrete for a project, for

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

which the use of concrete reinforced through traditional reinforcing techniques was originally foreseen. Standards for the design of fiber-reinforced concrete are under approval procedure, where criteria for calculation of the minimum reinforcement are prescribed. These will be also described in chapter 3 of the following publication, and may be applied to this design situation, being more elaborated.

On the other hand, other structural analysis and calculation methodologies are available, which can be easily adopted and comfortably adapted to the design of structural resistant elements made of fiber-reinforced concrete. These range from simpler analytical methods to more sophisticated and more versatile numerical approaches, such as methods which make use of powerful and widespread codes like SAP 2000®, or of other even more complex codes based on bi-dimensional or three-dimensional finite difference and finite element algorithms, such as ABAQUS®.

Input data necessary for sizing fiber-reinforced concrete supporting structures vary following the analysis method applied: in the simpler case based on the equivalence of flexural strength, only the value of the equivalent tensile strength of fiber-reinforced concrete on bending (f

eq) is required, while for numerical mod-

elling the detailed geometry of the structure, of the specific loads and of constraints (such as the stiffness of supporting soils, and particularly the modulus of reaction of the soil k), are required, besides, again, the value of the equivalent tensile strength of fiber-reinforced concrete on bending, and its modulus of elasticity.

Analysis results for supports of 10 m width tunnels will be illustrated, whereby numerical modelling has been conducted through the code SAP (Structural Analysis Program) of the University of California - Berkeley, for three of the already considered thicknesses of fiber-reinforced shotcrete (14 cm for P-b, 16 cm for P-c and 20 cm for P-d/e). The primary support P-a of thickness 10 cm was not analysed because its use is generally limited to cases with zero static loads or very low static loads, and its function is essentially to protect against possible localized accidental breakouts of small rock blocks from the heading and the faces of the excavation.

The most representing cases, between the numerical analyses conducted, are represented for what con-cerns maximum tensile stresses in critical areas of the structural section of the support (the vault and the faces). These are function both of the stiffness levels of the ground and of the loading schemes which have been considered for the analyses, which is: a uniform normal pressure over the whole perimeter of the supporting arch, and, more critically, again a normal pressure but of different intensity in the vault and in the faces (lateral pressure is gradually reduced only to a fraction towards the bottom of the arch).

Highest tensile stresses are obtained for those analyses simulating ground’s loads over the support having a reduced lateral pressure, while lowest tensile stresses, in contrast, are obtained for those analyses simulating uniform pressures over the whole perimeter of the support.

The most critical areas for what concerns the presence and intensity of tensile stresses in the support are those of the faces in contact with the ground; in analyses considering uniform pressure over the whole perimeter of the support, no tensile stresses are produced in the area of the vault, while in analyses considering reduced lateral pressure, tensile stresses produced in the area of the vault result being always lower than the ones generated at the faces.

Tensile stresses in the faces’ areas, which are generated as well in the case of uniform pressure over the whole perimeter of the support, are always higher, if a lower stiffness of the ground is considered.The highest tensile stress that has been obtained is equal to 9.0 kg/cm2 (0.9 MPa), followed by some other high values (8.2; 7.3; 5.7 and 3.9 kg/cm2). All the other maximum tensile stresses obtained are equal to 2.8 kg/cm2 (0.3 MPa), or lower.

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Table 5.10 - Values resulting from the analysis of the maximum tensile stresses in primary.

All the considered case studies, including the ones corresponding to the most unfavourable conditions as far as loads’ intensity and schemes are concerned, such as the stiffness of the ground, show how tensile stresses generated in supports result always being lower than 1 MPa, thus, being in principle always compatible with the characteristic equivalent tensile strength on bending that can be reached for shotcrete type C24/30 with minimum dosage of metal fibers (25 kg/m3), which is approximately 1.5 MPa according to various test results.

Numerical analyses allow thus to conclude that, from a strictly structural point of view, replacing welded wire mesh with a minimum dosage (25 kg/m3) of adequate metal fibers in shotcrete for tunnel supports is generally technically feasible, thereby confirming results obtained with simpler calcula-tions based on the equivalence between flexural strength of supports made of shotcrete reinforced through welded wire mesh and flexural strength of supports made of shotcrete reinforced through metal fibers.

In more general terms, numerical analysis allowed to demonstrate that by using adequate metal fibers in shotcrete type 24/30 (and obviously also of more elevated type), a fiber dosage of 25 25 kg/m3, such as indicated as minimum value for structural concretes by main standards, is in principle suf-ficient to provide to shotcrete a tensile strength (feq) as high as (1.0 –1.5 MPa), which is compatible with stresses that are generally generated in tunnels supports in the most common geotechnical, geometrical and covering conditions.

Loadscases

Supporttype

More rigidground

Less rigidground

Traction in walls

Lesser lateral pressureTractionwalls

Tractionroof

12345678910

(kg/cm )0.800.552.501.300.450.351.102.800.201.10

2 (kg/cm )0.940.562.531.500.510.411.542.801.302.90

2 (kg/cm )2.502.008.205.702.301.507.309.002.403.90

2 (kg/cm )2.101.303.302.601.500.904.103.701.502.20

2

P-c

P-cP-e

P-cP-dP-dP-d

P-dP-eP-d

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

To continue, the table related to the design of the primary support, obtained by the union of all analyses conducted, following what has been reported so far, is enclosed. The table can be carefully applied in order to produce an immediate preliminary design for a tunnel support having equivalent diameter in the order of 10 metres.

The first part of such table allows selecting the support on the base of the type of behaviour of the excavation, which can be referred to: the GSI (Geological Strength Index) for sections of tunnels below moderate coverings, and, for sections of tunnels of greater covering, to the Index of Competence: IC = s

cm/γ.H = (0.0034.m

i 0.8).s

ci[1.029+0.025.e (-0.1mi)]GSI/γ.H.

Table 5.11- Table representing average strength values obtained through bending tests following UNI11309.

Sanchon_ _1ATestSanchon_ _1BSanchon_ _1CSanchon_ _4ASanchon_ _4BSanchon_ _4CCorona_ _3ACorona_ _3BCorona_ _3CPila 4-2 27-8-04Pila 4-4 27-8-04Pila 1-2A 01-9-04Pila 1-2B 01-9-04Pila 1-2C 01-9-04Midium

TestTestTestTestTest

TestTestTest

Sample

Fiber FS3 (30/0,75)

4,53,74,34,22,63,03,52,72,82,82,62,83,12,53,22

Concrete C24/30

D x Do l

0,31110,26200,38650,40740,34580,44180,35170,67260,34820,38810,41670,43390,41810,56630,39

3,012,473,583,891,952,212,521,041,321,971,611,791,291,832,44

1,400,971,661,710,901,331,231,820,971,091,081,211,301,421,33

f(MPa)

(0,6-3)f(MPa)

(0-0,6)f/(MPa)

f

252525252525252525303030303025

Dosage(kg/m )3

Dos. 25kg/m2

f(MPa)

eqm

1,721,272,042,151,111,501,491,661,041,261,191,331,301,501,47

Table 5.12 - Type of behaviour of the excavation in function of:GSI –H - sci for tunnel of 10 m width or equivalent diameter.

G.Perri, 2002

7 8 9 10 11 12 13 14 15 16 17 18 19 20 23 25 28 30 35 40 45 50 60 70 80 90 100(m/MPa) mi

5 0,11 0,09 0,08 0,08 0,07 0,06 0,06 0,05 0,05 0,05 0,04 0,04 0,04 0,04 0,03 0,03 0,03 0,03 0,02 0,02 0,02 0,02 0,01 0,01 0,01 0,01 0,017,5 0,15 0,13 0,11 0,10 0,09 0,08 0,08 0,07 0,07 0,06 0,06 0,06 0,05 0,05 0,05 0,04 0,04 0,03 0,03 0,03 0,02 0,02 0,02 0,01 0,01 0,01 0,0110 0,18 0,16 0,14 0,12 0,11 0,10 0,10 0,09 0,08 0,08 0,07 0,07 0,07 0,06 0,06 0,05 0,05 0,04 0,04 0,03 0,03 0,02 0,02 0,02 0,02 0,01 0,01

GSI <=20 15 0,24 0,21 0,19 0,17 0,15 0,14 0,13 0,12 0,11 0,10 0,10 0,09 0,09 0,08 0,07 0,07 0,06 0,06 0,05 0,04 0,04 0,03 0,03 0,02 0,02 0,02 0,0220 0,29 0,26 0,23 0,21 0,19 0,17 0,16 0,15 0,14 0,13 0,12 0,11 0,11 0,10 0,09 0,08 0,07 0,07 0,06 0,05 0,05 0,04 0,03 0,03 0,03 0,02 0,0225 0,35 0,30 0,27 0,24 0,22 0,20 0,19 0,17 0,16 0,15 0,14 0,13 0,13 0,12 0,11 0,10 0,09 0,08 0,07 0,06 0,05 0,05 0,04 0,03 0,03 0,03 0,0230 0,40 0,35 0,31 0,28 0,25 0,23 0,21 0,20 0,19 0,17 0,16 0,15 0,15 0,14 0,12 0,11 0,10 0,09 0,08 0,07 0,06 0,06 0,05 0,04 0,03 0,03 0,0335 0,45 0,39 0,35 0,31 0,28 0,26 0,24 0,22 0,21 0,20 0,18 0,17 0,16 0,16 0,14 0,13 0,11 0,10 0,09 0,08 0,07 0,06 0,05 0,04 0,04 0,03 0,035 0,17 0,15 0,13 0,12 0,11 0,10 0,09 0,08 0,08 0,07 0,07 0,06 0,06 0,06 0,05 0,05 0,04 0,04 0,03 0,03 0,03 0,02 0,02 0,02 0,01 0,01 0,01

7,5 0,22 0,19 0,17 0,15 0,14 0,13 0,12 0,11 0,10 0,09 0,09 0,08 0,08 0,08 0,07 0,06 0,06 0,05 0,04 0,04 0,03 0,03 0,02 0,02 0,02 0,0210 0,26 0,23 0,20 0,18 0,17 0,15 0,14 0,13 0,12 0,11 0,11 0,10 0,10 0,09 0,08 0,07 0,07 0,06 0,05 0,05 0,04 0,04 0,03 0,03 0,02 0,02 0,02

GSI =(20-40) 15 0,33 0,29 0,26 0,23 0,21 0,20 0,18 0,17 0,16 0,15 0,14 0,13 0,12 0,12 0,10 0,09 0,09 0,08 0,07 0,06 0,05 0,05 0,04 0,03 0,03 0,03 0,0220 0,40 0,35 0,31 0,28 0,26 0,24 0,22 0,20 0,19 0,18 0,17 0,16 0,15 0,14 0,13 0,11 0,10 0,09 0,08 0,07 0,06 0,06 0,05 0,04 0,04 0,03 0,0325 0,47 0,41 0,37 0,33 0,27 0,25 0,24 0,22 0,21 0,19 0,18 0,17 0,16 0,15 0,13 0,12 0,11 0,09 0,08 0,07 0,07 0,05 0,05 0,04 0,04 0,0330 0,54 0,47 0,42 0,38 0,34 0,31 0,29 0,27 0,25 0,23 0,22 0,21 0,20 0,19 0,17 0,15 0,14 0,13 0,11 0,09 0,08 0,08 0,06 0,05 0,05 0,04 0,0435 0,60 0,53 0,47 0,42 0,38 0,35 0,32 0,30 0,28 0,26 0,25 0,23 0,22 0,21 0,19 0,17 0,15 0,14 0,12 0,11 0,09 0,08 0,07 0,06 0,05 0,05 0,045 0,26 0,23 0,20 0,18 0,16 0,15 0,14 0,13 0,12 0,11 0,11 0,10 0,09 0,09 0,08 0,07 0,07 0,06 0,05 0,05 0,04 0,04 0,03 0,03 0,02 0,02 0,02

7,5 0,32 0,28 0,25 0,23 0,21 0,19 0,17 0,16 0,15 0,14 0,13 0,13 0,12 0,11 0,10 0,09 0,08 0,08 0,06 0,06 0,05 0,05 0,04 0,03 0,03 0,03 0,0210 0,38 0,33 0,29 0,26 0,24 0,22 0,20 0,19 0,18 0,17 0,16 0,15 0,14 0,13 0,12 0,11 0,10 0,09 0,08 0,07 0,06 0,05 0,04 0,04 0,03 0,03 0,03

GSI = (30-50) 15 0,47 0,41 0,37 0,33 0,30 0,27 0,25 0,24 0,22 0,21 0,19 0,18 0,17 0,16 0,15 0,13 0,12 0,11 0,09 0,08 0,07 0,07 0,05 0,05 0,04 0,04 0,0320 0,56 0,49 0,43 0,39 0,35 0,32 0,30 0,28 0,26 0,24 0,23 0,22 0,20 0,19 0,17 0,16 0,14 0,13 0,11 0,10 0,09 0,08 0,06 0,06 0,05 0,04 0,0425 0,64 0,56 0,50 0,45 0,41 0,37 C 0,32 0,30 0,28 0,26 0,25 0,24 0,22 0,20 0,18 0,16 0,15 0,13 0,11 0,10 0,09 0,07 0,06 0,06 0,05 0,0430 0,72 0,63 0,56 0,51 0,46 0,42 0,39 0,36 0,34 0,32 0,30 0,28 0,27 0,25 0,22 0,20 0,18 0,17 0,14 0,13 0,11 0,10 0,08 0,07 0,06 0,06 0,0535 0,80 0,70 0,63 0,56 0,51 0,47 0,43 0,40 0,38 0,35 0,33 0,31 0,30 0,28 0,25 0,23 0,20 0,19 0,16 0,14 0,13 0,11 0,09 0,08 0,07 0,06 0,065 0,43 0,38 0,34 0,30 0,28 0,25 0,23 0,22 0,20 0,19 0,18 0,17 0,16 0,15 0,13 0,12 0,11 0,10 0,09 0,08 0,07 0,06 0,05 0,04 0,04 0,03 0,03

7,5 0,52 0,46 0,41 0,37 0,33 0,30 0,28 0,26 0,24 0,23 0,22 0,20 0,19 0,18 0,16 0,15 0,13 0,12 0,10 0,09 0,08 0,07 0,06 0,05 0,05 0,04 0,0410 0,59 0,52 0,46 0,41 0,38 0,35 0,32 0,30 0,28 0,26 0,24 0,23 0,22 0,21 0,18 0,17 0,15 0,14 0,12 0,10 0,09 0,08 0,07 0,06 0,05 0,05 0,04

GSI =(40-60) 15 0,71 0,62 0,55 0,49 0,45 0,41 0,38 0,35 0,33 0,31 0,29 0,27 0,26 0,25 0,22 0,20 0,18 0,16 0,14 0,12 0,11 0,10 0,08 0,07 0,06 0,05 0,0520 0,81 0,71 0,57 0,52 0,47 0,44 0,41 0,38 0,36 0,34 0,32 0,30 0,28 0,25 0,23 0,21 0,19 0,16 0,14 0,13 0,11 0,09 0,08 0,07 0,06 0,0625 0,92 0,81 0,72 0,65 0,59 0,54 0,50 0,46 0,43 0,40 0,38 0,36 0,34 0,32 0,29 0,26 0,23 0,22 0,18 0,16 0,14 0,13 0,11 0,09 0,08 0,07 0,0630 1,03 0,90 0,80 0,72 0,66 0,60 0,56 0,52 0,48 0,45 0,42 0,40 0,38 0,36 0,32 0,29 0,26 0,24 0,21 0,18 0,16 0,14 0,12 0,10 0,09 0,08 0,0735 1,14 1,00 0,89 0,80 0,73 0,67 0,62 0,57 0,53 0,50 0,47 0,44 0,42 0,40 0,36 0,32 0,29 0,27 0,23 0,20 0,18 0,16 0,13 0,11 0,10 0,09 0,085 0,94 0,82 0,73 0,66 0,60 0,55 0,51 0,47 0,44 0,41 0,39 0,37 0,35 0,33 0,29 0,26 0,24 0,22 0,19 0,16 0,15 0,13 0,11 0,09 0,08 0,07 0,07

7,5 1,07 0,94 0,83 0,75 0,68 0,63 0,58 0,54 0,50 0,47 0,44 0,42 0,40 0,38 0,33 0,30 0,27 0,25 0,21 0,19 0,17 0,15 0,13 0,11 0,09 0,08 0,0810 1,16 1,02 0,90 0,81 0,74 0,68 0,63 0,58 0,54 0,51 0,48 0,45 0,43 0,41 0,36 0,33 0,30 0,27 0,23 0,20 0,18 0,16 0,14 0,12 0,10 0,09 0,08

GSI > 60 15 1,30 1,14 1,01 0,91 0,83 0,76 0,70 0,65 0,61 0,57 0,54 0,51 0,48 0,46 0,41 0,36 0,33 0,30 0,26 0,23 0,20 0,18 0,15 0,13 0,11 0,10 0,0920 1,44 1,26 1,12 1,01 0,92 0,84 0,78 0,72 0,63 0,59 0,56 0,53 0,51 0,45 0,40 0,37 0,34 0,29 0,25 0,22 0,20 0,17 0,14 0,13 0,11 0,1025 1,60 1,40 1,24 1,12 1,02 0,93 0,86 0,80 0,75 0,70 0,66 0,62 0,59 0,56 0,50 0,45 0,41 0,37 0,32 0,28 0,25 0,22 0,19 0,16 0,14 0,12 0,1130 1,76 1,54 1,37 1,23 1,12 1,03 0,95 0,88 0,82 0,77 0,73 0,69 0,65 0,62 0,55 0,49 0,45 0,41 0,35 0,31 0,27 0,25 0,21 0,18 0,15 0,14 0,1235 1,94 1,70 1,51 1,36 1,23 1,13 1,04 0,97 0,91 0,85 0,80 0,75 0,71 0,68 0,60 0,54 0,49 0,45 0,39 0,34 0,30 0,27 0,23 0,19 0,17 0,15 0,14

E

D

B

A

CLASS OF BEHAVIOUR OF THE EXCAVATION IN FUNCTION - H - ciciH/

ABILITY INDEX (IC = cm/yH)

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

The second part of the table describes basic geometrical and structural characteristics of the sup-ports mentioned, for which, according to the principal structural element identifying those supports that is fiber-reinforced shotcrete, the related minimum equivalent tensile strength on bending (f

eq)

referentially recommended for each case, is indicated.

DESIGN OF THE PRIMARY SUPPORT: Tunnel of width ~ 10 m

COVERINGS < 20 m

GSI <= 20

20< GSI <= 40

30< GSI <= 50

40< GSI <= 60

GSI > 60

SP-e

SP-e

SP-d

SP-c

SP-c

COVERINGS 20 - 100 m

GSI <= 20

20< GSI <= 40

30< GSI <= 50

40< GSI <= 60

GSI > 60

SP-e

SP-d

SP-c

SP-b

SP-a

COVERINGS > 100 m

IC<=0.15

0.15< IC<= 0.20

0.20< IC<= 0.30

0.30< IC<= 0.45

IC > 0.45

SP-e

SP-d

SP-c

SP-b

SP-a

Table 5.13 - Supports classification for tunnels of 10 meters of diameter in function of the GSI.

5.4 - Design of lining made of fiber-reinforced concrete pumped on-site.

The table for the design of a support made of fiber-reinforced shotcrete, eventually integrated with metal spiles and/or ribs, that is reported in the previous chapter, refers to a support conceived as a primary support, which foresees the subsequent construction of a final lining. The primary lining shall be realized by considering safety and reliability requirements that correspond to a permanent structure, as it should fulfil the objective of stabilizing the excavation in the short term, thus considering a relatively low safety factor (e.g. 1.1 to 1.5), or, what is the same, a relatively high defect probability (e.g. 1% to 5%).

If in contrast, the fiber-reinforced shotcrete structure would be conceived as the only permanent structure to be applied for the structural support of the tunnel, as it is often the case in modern en-gineering when geomechanical and geostructural conditions of the excavation are contained within non-critical limits, and when functional characteristics of the tunnel enable such a situation, then, it would be necessary to design such structure by considering much higher safety factors, or much lower defect probabilities.

SUPPORT Shotcrete(fiber-reinforced) Metal ribs Metal Spiles (20 t)

10 cm (f = MPa)eq 1,0 -

14 cm (f = MPa)eq 1,1 2 x 4 m each two ribs

4 x 4 m each two ribs

6 x 6 m each two ribs

10 x 6 m each two ribs

16 cm (f = MPa)eq 1,2

SP-a

SP-b

SP-c

SP-e 20 cm (f = MPa)eq 1,4

-

2 IPN160each 125 cm

20 cm (f = MPa)eq 1,3SP-d 2 IPN200each 100 cm

2 IPN200each 075 cm

2 IPN160each 150 cm

Table 5.14 - Example of specification of resistance required for the concrete reinforced with fibers in the primáry support of tunnels.

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Requests ofcontainment

Interactioncontainment-ground

Figure 5.5 - Basic scheme of structural model for final lining.

In a first approximation, the design of such a type of structure, constituting in fact the final lining of the tunnel, can be carried out on the base of the same principles and procedures as illustrated before with reference to primary supports, whereby the required safety and reliability factors characteristic of a permanent final lining must be included in calculations.

By proceeding in the same way for the same five types of behaviour of excavations that were previously defined in function of the GSI and the IC, respectively for moderate and for high coverings, results summarized in the following tables are obtained for tunnels with approximate equivalent diameter of 10 metres. Tables are as well in accordance with numerical results of corresponding systematic structural analyses that were conducted, in a similar way to the ones reported afterwards, for linings made of cast-in-place concrete.

Final linings result having a minimum thickness of 20 cm, and, in order to apply fiber-reinforced shot-crete, this should have more demanding mechanical characteristics, which should be characterised by tensile strength not lower than 1.5 MPa (f

eq >=1.5 MPa), capable to provide high and permanent

flexural strength to resistant sections of the lining’s structure.

COVERINGS < 20 m COVERINGS 20 - 100 m COVERINGS > 100 m

GSI < = 20

20 < GSI < = 40

RD - e

RD - e

30 < GSI < = 50

40 < GSI < = 60

GSI > 60

RD - d

RD - c

RD - c

GSI < = 20

20 < GSI < = 40

RD - e

RD - d

30 < GSI < = 50

40 < GSI < = 60

GSI > 60

RD - c

RD - b

RD - a

IC < = 0.15

0.15 < IC < = 0.20

RD - e

RD - d

0.20 < IC < = 0.30

0.30 < IC < = 0.45

IC > 0.45

RD - c

RD - b

RD - a

Table 5.15 - Basic project of structural model for the definitive covering.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.16 - Project of the definitive covering in shotcrete reinforced with fibers (*),

Type oflining

Fiber-reinforcedShotcrete Metal ribs Metal spiles 20 t

RD - a

RD - b

RD - c

RD - d

RD - e

20 cm1,5(f >= MPa)eq

20 cm1,5(f >= MPa)eq

25 cm1,5(f >= MPa)eq

25 cm1,5(f >= MPa)eq

- -

2 IPN200 @ 150 cm 2 x 4m @ each two ribs

or, alternatively 7 spiles x 4m @ 150 cm (without ribs)

2 IPN200 @ 125 cm 2 x 6m @ each two ribs

or, alternatively 11 spiles x 6m @ 125 cm (without ribs)

2 IPN200 @ 100 cm

2 IPN200 @ 075 cm

6 x 6m @ each two ribs

10 x 6m @ each two ribs

or, alternatively 15 spiles x 6m @ 100 cm (without ribs)

30 cm1,5(f >= MPa)eq

The abovementioned numerical structural analyses have been conducted systematically for linings of tunnels of 10 m net diameter, considering good quality concrete (C32/40), cast-in-place, and considering three possible thicknesses (30 - 40 - 50 cm). The two already defined possible covering conditions (low and high) were analysed, and two different geomechanical ground qualities were simulated (GSI lower than 40 or GSI higher than 40).

Detailed results are reported in the enclosed table that includes, for each of the sixteen simulated cases, maximum tensile stresses reached in the intrados of the keystone and in the extrados of both faces of the lining section.

In the inverted vault arch, that is considered as being present in every model with a bending radius equal to three times the radius of the main arch of the section, tensile stresses in the intrados result being almost always high. As a consequence, they should be more efficiently absorbed by classical reinforcement.

(*) For tunnels with approximate width, or equivalent diameter, of 10 metres.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

One of the results obtained through numerical analyses is reported as an example, whereby principal maximum stresses in the tunnel’s lining section are graphically represented.

Figure 5.6 - Scheme of design loads for the final lining.

Scheme of design loads for the final lining

Unstable edge

Rn

Gravity effect

Decompression is accompained by the formationof a unstable zone above the crown which mighteventually colapse

– Gravity effect on decompressed zone

Table 5.17 - Maximum traction strenght in the covering gotten of the numerical analyses.

LININGS IN LOW COVERINGS

1 RF2-Pc16 RF2-Pc2 RF2-Pd3 RF2-Pd4 RF2-Pd5 RF2-Pc6 RF17 RF2*8

24.60 2.4312.50 0.9542.20 7.4032.60 4.3016.70 2.104.80 0.571.83 0.3546.60 11.6044.95 10.80

131.50 101.7034.40 11.60221.00 178.10175.50 141.8053.30 12.8027.50 4.3015.40 0.76276.30 250.00165.30 216.70 RF2-Pd

LININGS IN HIGH COVERINGS

9 0.60 0.40 1.52 1.90 RF110 1.20 0.70 6.60 0.83 RF2-Pc11 0.29 0.16 0.70 0.75 RF112 2.40 4.20 20.50 1.60 RF2-Pd13 0.65 0.31 3.60 0.00 RF2-Pc14 4.20 1.65 55.40 1.80 RF2*15 3.70 2.41 32.70 2.70 RF2-Pd

LININGCASESType

More rigid groundTractionroof

Tractionwalls

(Kg/cm )2 (Kg/cm )2

Less rigid groundTractionroof

Tractionwalls

(Kg/cm )2 (Kg/cm )2

LININGCASESType

More rigid groundTractionroof

Tractionwalls

(Kg/cm )2 (Kg/cm )2

Less rigid groundTractionroof

Tractionwalls

(Kg/cm )2 (Kg/cm )2

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Finally, the following table summarizes numerical values of maximum tensile stresses obtained in the vault and in the faces, for each of the three lining thicknesses considered, for the two covering conditions analyzed, and for the different geomechanical qualities simulated for grounds.

Figure 5.7 - Graphical example of principal maximum stresses in the lining.

Table 5.18 - Maximum tensile stresses in the vault and in the faces (MPa).

0.18

4.49

4.66

1.54

22.1

27.63

0.06

0.37

0.42

Maximum tensile stresses in the vault and in the faces (MPa)

Low coverings ( Hs)<

Less rigidground

More rigidground

RF (30cm)

RF (40 cm)

RF (50cm)

LiningsHigh coverings (> Hs)

0.19

3.27

5.54

Less rigidground

More rigidground

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By analysing all the numerical results obtained, the following can be observed:

- For sections of tunnels characterized by ¨low coverings¨, if one refers to geotechnical condi-tions characterized by grounds having little hardness, and with except for few cases characterized by very little loads that are a seldom exception for low coverings, tensile stresses generated in the vault and in the faces result generally being highly incompatible with equivalent tensile strengths on bending that are achievable in fiber-reinforced concretes, independently from concrete type and also from dosage of metal fibers to be possibly applied.

If, in contrast, one refers to geotechnical conditions characterised by relatively hard grounds, that is grounds having high moduli of reaction as well as good geomechanical characteristics (GSI > 40), tensile stresses generated in the vault and in the faces result being relatively low, thereby being always lower than 5 MPa, and lower than 3.5 MPa in at least one third of analyzed cases (moreover, in the faces, they reach maximum values of the order of only 1 MPa).

Although in some of these cases tensile stresses result being quite important, they are still compat-ible with a fiber-reinforced concrete produced by applying a high quality and high dosages of metal fibers, both for linings of 40 cm thickness and for linings of 50 cm thickness.

Finally, for exceptionally good geomechanical conditions (GSI > 60), tensile stresses may result neg-ligible, also in the case a lining of only 30 cm thickness is applied.

- For sections of tunnels characterized by ̈ high coverings¨, if one refers to geotechnical condi-tions characterized by relatively hard grounds, that is grounds having high moduli of reaction as well as good geomechanical and geostatic conditions (GSI > 40 e IC > 0.45), tensile stresses generated in the vault and in the faces result always being very low, thereby being lower than 0.5 MPa. Thus, as a consequence, they result being globally compatible with a normal selection of fiber type and fiber dosage, also for linings of only 30 cm thickness.

If, in contrast, one refers to geotechnical conditions characterised by grounds having little hardness, although tensile stresses generated in the faces still remain largely within very low limits (lower than 0.5 MPa), stresses generated in the vault are relatively high, with except for few cases characterized by little loads that are a seldom exception for high coverings. Thus, they oblige differentiating in function of ground’s geomechanical quality (GSI lower than 40 or GSI higher than 40) and geostatic conditions of the section (IC lower than 0.20 or IC higher than 0.20):

In the case of ground and tunnel section characterized by good geomechanical and geostatic condi-tions (GSI > 40 and IC > 0.20), tensile stresses generated in the case a 40 cm thick lining is applied are only relatively high (slightly higher than 3 MPa). Thus, as a consequence, good compatibility still exists with equivalent tensile strengths on bending that are achievable with a fiber-reinforced concrete produced by applying a high quality and high dosages of metal fibers.

In contrast, in the case of ground and tunnel section characterized by poor geomechanical and geostatic conditions (GSI < 40 and IC < 0.20), tensile stresses generated in the vault, although a 50 cm thick lining is applied, are very high (higher than 5 MPa). As a consequence, they are practically incompat-ible with any equivalent tensile strength on bending of any excellent fiber-reinforced concrete.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Finally, in conclusion of this chapter dealing with geostructural design of final linings of tunnels made of fiber-reinforced both shotcrete and cast-in-place concrete, it is absolutely necessary to highlight that methodologies indicated and, above all, results summarized in the design tables enclosed, should in no case be considered completely exhaustive in order to proceed to an executive design of a tunnel. This is because such results could not take into due account all peculiarities, which might characterize real circumstances, as these could often become non-usual and possibly critical in function of real geologic and construction conditions related to a specific tunnel section.

On the contrary, the reported methodologies and results may be very useful in order to proceed to a correct preliminary design of a tunnel. They may be even efficiently and successfully applied in real circumstances, in the case of designs characterized by almost coinciding geomechanical, geostatic and construction conditions, by taking into account the basic assumptions that average represen-tative cases have been considered as far as behavioural models are concerned, for all the analyses conducted over design conditions presented in this chapter for tunnels’ final linings constructed by applying traditional excavation methods.

Project of the final covering in fibers reinforced concrete placed in situ

Table 5.19 - For tunnels of approximately 10 meters of width or diameter equivalent.

COVERING Hi< Hi < COVERING Hs< COVERING > Hs

20 < GSI 40<

40 < GSI 60<

GSI > 60

GSI 20RF reinforced

<

20 < GSI 40< RF(50 cm)

RF(40 cm)

RF(30 cm)

40 < GSI 60<

GS > 60

0,20 < IC 0,30<

0,30 < IC 0,45<

IC > 0,45

RFreinforced

RF(50 cm)

RF(40 cm)

RF(40 cm)

RF(40 cm)

RF(30 cm)

Characteristics of the concrete fiber reforced placed in situ.

RF reinforced

RF reinforced f > = 5 MPaeq

RF (40 cm)

RF (30 cm)

f > = 4 MPaeq

f > = 2 MPaeq

5.5 - Use of fibers for fire resistance of concrete. Description of fiber mixes, structural and anti-spalling proposal for final linings.

Tunnels’ structures are commonly designed to withstand actions to which they will be exposed to for their entire life-cycle. Nevertheless, there is an additional phenomenon which must be taken into

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The fact that tunnels are confined structures and that, in the event of a fire, flames come directly in contact with the concrete of the structure, makes temperatures reaching very high values. Thus, rapid degradation of the structure takes place if no protection measure has been taken against fire.

The exposure of construction elements to high temperatures has the consequence that physical and mechanical characteristics of such elements are altered, with the result that their structural functionality is thereby reduced. In the specific case of concrete, degradation occurs stepwise with increasing tem-perature levels. A graphical representation of degradation can be observed in the following figure:

Table 5.20 - Summary of structural damages related to recent tunnel fire events.

Tunnel(year)

Concretestrength

Maxtemp

Fireduration

Lengthaffected

Great Belt(1994)

76 MPa28 day

800 ºC -1,000 ºC 7 hrs

16 segment rings(1.65 long)

damaged in crown

Channel(1996)

110 MPamature 1,000 ºC 9 hrs

500 m with 50 mseverely affected

by spalling

Mont Blanc(1999) Not reported 1,000 ºC 50 hrs

900 m – tunnelcrown most affected

Affect on segment

Peak of spalling270 mm

Up to 100% (400 m)of thickness spalled

showing grout

Serious damageto tunnel structure

Graphic 5.3 - Increase in Temperature vs. Concrete Degradation.

Temperature Increase vs. Concrete Degradation

0

200

400

600

800

ºC

Frontal face collapse“spalling”

First crackingappearance

Bearing capacityhalf reduction

account when designing tunnels’ supporting structures, which is exposure to fire.

The risk of the occurrence of a fire is high in tunnels. Moreover, following recent accidents occurred in various tunnels all over the world, characterized not only by structural damages but also by loss of human lives, the design of fire resistant structures has become an absolute priority both for standard-izing entities and for designers.

The primary function that has to be fulfilled by any type of fire protection instrument in tunnels is to leave people sufficient escape time, besides assuring sufficient mechanical strength of the structure so as to enable firefighters to enter the tunnel and extinguish the fire. It becomes therefore clear that it is principally in the initial phases of a fire that a passive protection measure should come into action.

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yz

xConcrete

Spall

Load andthermal stresses

L

I

Pore pressure P

L I+

Figure 5.8 - Graphical representation of the “spalling” phenomenon.

Concrete melted

Melting starts

Ceramic bindingTotal loss of water of hydration

Marked increase in “basic” creepα β Inversão expansiva do quartzo

Calcium hydroxide dissociatesTriple point of water

Thames river gravel breaks up

Start of siliceous concreteStrength loss

Hidrothermal reactionsLoss of chemically bound water starts“Hot” permeability increases markedly

Free water lost at 1 atm

1,400ºC

1,300ºC

1,200ºC....

800ºC

700ºC

600ºC

500ºC

400ºC

300ºC

200ºC

100ºC

20ºC

Co

ncre

testr

uctu

rally

no

tu

se

ful

Exp

losiv

esp

alli

ng

(su

rfa

ce

tem

pe

ratu

re)

Dissociation of calcium carbor ate

Some flint aggregates dehydrate

Figure 5.9 - Physico-chemical reactions taking place in the concrete’s structure with temperature increase.

As it can be observed in Fig. 5.8, the first phenomenon occurring by an increase in temperature is crumbling of the surface layer (spalling). As soon as the concrete’s surface temperature increases, most of the water vapour, that is present in concrete, will migrate towards the inside part, where lower temperature conditions exist. The consequence to this phenomenon is an increase in internal pressure of the cement matrix up to the point at which the concrete’s characteristic strength is over-come, and at which spalling (crumbling of the surface layer) takes place.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

It is evident that a fire’s intensity will depend from the materials originating the fire. Thus, when designing a protection against fire for concrete, one should take into account the type of vehicles passing through the tunnel. Nowadays, different standards propose various heating curves, which give the designer the opportunity to select the one that is most representing of the specific tunnel situation. The European Norm EN1363-1-2/1999 defines two types of curves that can be used:Standard (for low fire intensity): T = 345 . Log

10.(8.t + 1) + 20

Hydrocarbons (for fires of higher intensity): T=1080.(1– 0.325 . e-0.167.t – 0.675 . e-2.5.t) + 20

Where:t: is the time, in minutes, calculated from the beginning of the test;T: is the average temperature required in the furnace in ºC.

Graphic 5.4 - Example of heating curves following different European codes.

Furnacetemperature(ºC)

1400

1000

600

200

00 5 10 30 60 90 120 150

Time (minutes)

RWS (NL)ZTV (D)Hydocarbon (EC)Standard ISO or BS 476

5.5.1 - Objective of passive protection of concrete against fire.

The principle objective that has to be achieved by any passive protection of concrete against fire is to avoid loss of human lives by acting in such a way that mechanical characteristics of structural elements are kept stable during the tunnel evacuation process and the intervention of firefighters. Structural characteristics that should be guaranteed for passive protection are:

a) Preservation of the supporting capacity. b) Avoided emission of flammable gases in the exposed face. c) Avoided dissipation of flames or gases. d) Thermal insulation towards the internal part of the structural element.

Thus, it may be concluded that the whole passive protection of concrete against fire should play an important role during the first minutes in which it is called to take action, given the fact that it is in such period of time that evacuation of people would take place and that firefighters would try to extinguish the fire.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

5.5.2 - Polypropylene and cellulose fibers as passive protection of concrete against fire.

Recent studies have allowed to conclude that the addition of micro-fibers of polypropylene (mono-filament type, with diameters lower than 32 mm) or of cellulose to the matrix, significantly reduces the occurrence of “spalling” in concrete during a fire. Moreover, those studies have allowed to conclude that a directly proportional correlation exists between the number of fibers embedded in the matrix and the improvement of the concrete’s behaviour with respect to fire.

The mechanism following which polypropylene fibers contribute to reduce the “spalling” phenomenon is rather simple. When the temperature of 160°C is reached, polypropylene fibers melt, thereby reduc-ing their occupied volume. When the temperature of 360°C is reached, polypropylene evaporates, thereby forming a set of small conduits within the matrix, which arrive up to the surface.

Those small conduits are utilized as well by the gases which are produced due to evaporation of water within the concrete. In this way, pressure is reduced and crumbling of the surface layers is avoided.

As it can be observed in degradation of concrete by increasing temperature, the phenomenon which should be primarily controlled is “spalling”, since this is the principal degradation phenomenon which concrete would suffer during the initial minutes of a fire.

Before any kind of protection against fire is utilized, it is important to study the behaviour which is produced by such protection in concrete. Although there is currently no standards to be applied for tests of fire resistance of concretes to be applied for tunnelling, it is recommended that the European standard EN 1363 –1 and 2 (2000) is applied, regulating fire resistance tests. Here, procedures for tests are described.

Figure 5.10 - Escape ways of gases within the matrix.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Figure 5.11 - Detail of the evaluated prismatic element, with a reinforced of 30 mm. All dimensions are in mm.

Specimens with three different types of mixtures have been tested: - Normal concrete mixture without the insertion of fibers. - Mixture with insertion of polypropylene fibers. - Mixture with insertion of cellulose fibers.

Various opinions exist referring to the quantity of fibers which should be embedded in the matrix in order to offer efficient protection. What is evident, however, is that the higher is the number of fibers, the better will be the results. Currently, recommendations concerning the minimum dosage of fibers indicate a volume percentage of ≥ 0.2 % (corresponding to 1.82 kg/m3). This evidently depends from the quality of concrete, since the application of high resistance concretes would imply a higher requirement for protection, thus higher dosages.

In order to provide a clearer graphical representation of the effect of this material, in the following section a summary of experiments conducted over specimens exposed to the heating curve as pro-posed by standard EN 1363-1-2/1999 is presented.

Photo 5.11 - Example of a specimen in the testing furnace.

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The different behaviours in the different stages of the heating curve proposed by standard EN 1363-1-2/1999 have been evaluated, and the mass losses of the material have been evaluated during the same curves. With the insertion of fibers, excellent results have been obtained, and the final objec-tive of maintaining integrity of the element for a period of time that was safely corrected to assure the possibility to evacuate from structures which are accidentally exposed to a fire, has been thereby achieved.

Case of cellulose fibers

Photo 5.12 - Specimens evaluated with cellulose fibers.

Water drops on the material surface, produced by the increase in temperature.

Photo 5.13 - Specimens evaluated with cellulose fibers.

Photo 5.14 - Samples of material lost due to superficial “spalling” in specimens with cellulose.

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Relatively to the behaviour of specimens prepared with mixture, in which cellulose fibers had been inserted, a good behaviour has been observed, as only a light “spalling” has been produced after 8 minutes of testing. Moreover, subsequently, and up to the end of the test, no significant loss of material mass was observed

Photo 5.15 - Specimens of material with use of polypropylene fibers. Specimen after the end of the test.

Case of polypropylene fibers

Photo 5.16 - Specimens with polypropylene fibers. To be observed superficial watering due to the loss of water and vapour.

In the test of specimens with addition of polypropylene fibers, an adequate behaviour, with a mini-mum loss of mass produced by the physico-chemical reactions already reported in previous sections, has been observed during the whole heating curve. Moreover, over these specimens, an almost null effect of “spalling” has been observed.

Case of specimens without fibers

Photo 5.17 - Example of experimental specimens without use of any type of fibers.

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Photo 5.18 - Samples of material that have detached due to “spalling” during testing of specimens without fibers.

The degradation degree is evident that can reach a structure without any type of protection. During the experimental process, a begin of “spalling” has been observed in the initial 3 ÷ 8 minutes of the test. Thereby, significant additional loss of material has been observed, which can be considered as being caused by the loss of water or of vapour due to heating of the material.

To summarize, and in order to provide an exemplifying comparison between the loss of mass related to the three different types of specimens that have been tested, the following graph showing mass loss is shown:

Graphic 5.5 - Graph showing a comparison between the loss of mass related to the different experimented specimens.

�2 4

�2 2

�2 0

�1 8

�1 6

�1 4

�1 2

�1 0

�8

�6

�4

�2

00 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Time (minutes)

Perte

sde

mas

se(%

)

Fibers CF16 Prisme 1 Fibers CF16 Prisme 2Fibers PP18-18 Prisme 1 Fibers PP18-18 Prisme 2Sans fibers Prisme 1 Sans fibers Prisme 2

As a final reference to the present theme related to protection of concrete structures against the effects of fire, it is fundamental to highlight that the use of fibers provides an effective solution for new works. This generates that emphasis that is currently given by technicians to this kind of solution especially in the case of underground work designs, considering the fact that those types of projects have a highly significant economical, social as well as political importance, and considering the fact that any kind of failure or accident which might occur would have irreversible consequences.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

5.6 - Quality control of fiber-reinforced concrete in tunnels.

Quality control of fiber-reinforced concrete in an underground work is fundamental, since concrete is one of the principal components forming the supporting structure in the case the latter is of primary type, of final type, or is made of precast elements such as segment rings.

As it has been highlighted in previous chapters, the presence of concrete as fundamental element in the supporting structure of an underground work is specified by detailed mechanical properties that must be assured during the whole life cycle of the work. Mechanical properties such as compressive, and flexo-tensional strength, are the principal mechanical characteristics that must be accurately evaluated. They will depend from a rigorous composition of the mixture. Quality controls on ag-gregates, cement, water-cement ratio, additives selection already discussed within chapter 4 of the present publication, constitute the basis to manage to obtain a mixture that guarantees mechanical specifications considered in the design of the whole structure.

Available mixtures to be employed for the design of an underground work are:

- Mixture for sprayed concrete. It can be used both as primary lining, and as final lining in an underground work, primarily depending from the type of work, whether it is underground hydraulic, for rail or street transport, pedestrian, etc.

- Mixture for pumped concrete. Commonly applied in case of final linings, upset archs, and other structural elements of a final lining. This type of mixture is applied for elements such as ring segments, that are immediately used as final lining.

All these choices for concrete have been exemplified at the elaboration level within chapter 4. In the current chapter, technical considerations leading to the need for quality control on the material will be reported.

The design of a tunnel supporting structure is influenced by the type of mechanical and functional characterization, as specified below:

Mechanical characterisation: - Structural - Non-Structural

Functional characterisation: - Temporary - Permanent

What has been hereby presented by means of this document, reports about experiments and consid-erations related to materials produced by MACCAFERRI. In any case, good technical practices foresee material suppliers to demonstrate quality adequateness of materials, as well as compliancy of their behaviour with heating curves foreseen by the project design.Various options exist as well for protection of existing structures. These proposals may be considered as well for the type of underground works of which it is reported within this document. Neverthe-less, particular attention should be paid to the development of solutions for protection of structures against fire.

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Combinations of these terms will lead to different analyses having following conditions, ordered by importance:

- Non-Structural Temporary. Regularly, in excavations of self-supporting systems, where the lining just provides a function of sealing the surface in order to avoid its degradation due to exchanges with the atmosphere that may occur between the surface of the fresh rock and its diaclases, or fractures on the surface of the rock mass. These may be activated by the exchanges with the new environment, and, as a result, they may generate partial detaching of blocks, which might become an operational hazard, even if they do not produce a structural disequilibrium in the excavation. This kind of supports complies with behaviours of type “a” that have been discussed in chapter 5.2 of the present publication, where deformations of the arch are not foreseen. Generally, they are characterized by very low thicknesses, ranging from 3 cm to 5 cm, they are realized with sprayed concrete, both by dry or wet systems, and are put in place during the first phase of the excavation of an underground work.

- Non-Structural – Permanent. This type of lining has the same functional characteristics as the ones described for the type “Non-Structural – Temporary”, with one difference, that is the fact that, at the design level, it may be increasingly loaded in order to be considered as a permanent lining within the work. It is generally realized with sprayed concrete, both using dry or wet systems. In this case, higher thicknesses are foreseen, that may be in the order of 10 - 15 cm. Occasionally, it may be combined with the use of dispersed anchorage spiles to be applied in those areas from which blocks may potentially detach, with the objective of increasing the safety factor of the work as a whole. Another alternative exists that may be also included within this class, that is final linings made of concrete that has been pumped on-site in mobile moulds. Though this alternative has a permanent character as well, in this case, it provides no structural function. Instead, it is only fore-seen as finishing for the section of the underground work, whereby all the structural responsibility for the underground excavation is assigned to the primary lining, which has been properly designed to fulfil this function. As an example of geomechanical behaviour corresponding to this functional classification, areas of behaviours type “a” and “a/b”, as reported within chapter 5.2 of the present publication, may be mentioned for the case of supports made of sprayed concrete.

- Structural – Temporary. This type of linings, generally realized in the first phase of the exca-vation, correspond to heavier linings when compared to the previous ones, since these are effectively put in place to withstand loads generated by the rock mass and/or by the layer of ground through which the underground work passes. Having temporary characteristics, these linings are designed by considering low safety coefficients, ranging from 1.2 to 1.5, with the objective of providing tem-porary containment, while the subsequent construction of a final lining is taken into account, which would take over final responsibility for the whole supporting system of the work, and which would be characterized by greater safety factors. These linings are generally realized by using a set of sup-porting elements such as sprayed concrete, anchorage spiles, occasionally metallic profiles known as centres or ribs, and even piles’ or micro-piles’ systems, jet-grouting when geomechanical zones are very week, thus requiring an action of this kind. The combination of these elements manages to stabilize the excavation, and, in this case, thicknesses of sprayed concrete are in the order of 15 cm up to 30 cm. Moreover, they may arrive to 45 cm in the case of particularly unfavourable areas. Pumped concrete is not applied in this particular case. In order to provide a reference to the type of lining that may be included in this functional classification, supports of types a”, “b”, “c”, “d” and “e” are extensively discussed within sub-chapter 5.2 of the present publication.

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- Structural – Permanent. In this functional classification supports previously denominated as “Structural – Temporary” supports may be included. However, in order to be considered as perma-nent, these should be designed by considering safety factors higher than the ones reported in the previous section, and specifically by considering minimum values between 2 and 2.5. This results in a set of supports having the same structural conception as before, but being evidently characterized by a higher stress level due to the increase in the safety factors. This is valid for the case of linings which make use of sprayed concrete. In this functional classification final linings made of pumped concrete may be included as well. Moreover, also the case of precast elements such as ring segments that are placed in a tunnel excavation by TBM (Tunnel Boring Machines) or EPB-TBM (Earth Pressure Balanced - TBM) machines may be included. It should be highlighted, however, that a TBM system is not only related to the placement of ring segments; currently, other machines are available which allow the lining being put in place through the use of robots for sprayed concrete, whereby also this latter use is considered within the functional class “Structural – Permanent”. Once the functionality of the supporting system has been explained, the presence and the feasibility of putting in place fiber-reinforced concrete, either sprayed, pumped, or applied by using precast segments, can be highlighted, as it has been extensively reported in the previous chapters.

The concept of quality control should be directly oriented towards the functionality of the support, whereby the latter is directly related to the concept of deformability of the supporting structure. This opens up two possible criteria - about which nowadays it is very much discussed between specialized consultants of the sector - regarding the configurations of fiber-reinforced concretes for underground works. They propose to orient control and/or the requirements for fiber-reinforced concrete in the following way:

- Supports with possible deformability up to the achievement of the stability of the excava-tion. Following the criterion of functionality that has been set out above, these may be “Temporary – Non-Structural” or “Temporary Structural”, whereby the criterion of deformation of the support is allowed with wide tolerances, without leading to collapse of the structure. For this type of sup-ports, quality control is directly oriented towards testing of Absorbed Energy or towards Plates Tests of types EFNARC and/or ASTM C1550. What is sought by applying this concept, is to guarantee that the ductility of the material is such that it is compatible with deformations foreseen for this type of support. It is for this reason, that this type of testing investigates the behaviour of the material for high deformations in the order of 25 to 40 mm. Currently, a wide discussion exists regarding the effectiveness of the two abovementioned tests related to the statistic dispersion that is obtained by them, and regarding the possibility to manage to compensate for this by means of an adequate performance classification taking this variable into account.

- Structural supports without deformation. Within this concept, functional classifications defined as “Permanent – Non-Structural”, for the case of pumped final linings, and “Permanent – Structural”, in all its possibilities, are considered. Since these are the definitive structures of a lining, the majority of them are conceived so as to avoid generating deformations, as these should be con-trolled during the excavation of a primary support that should control this effect in a primary phase. These may be also conceived as primary supports with a high safety factor, having the objective to mitigate by 100% the possibility of an immediate deformation of the excavation. For this type of supporting structures, which can be realized by using fiber-reinforced concrete, the equivalent re-sidual post-cracking strength is applied within limits set by the norms on structures. The mechanical

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

characterization of the material towards the structural design is made by bending test of types ASTM C1018, ASTM C1399, UNI 11039, Eurocode EN 14487-1.

An adequate quality control depends on the definition of the support’s function. It is at this point that the need for bending tests as well as for plates tests is generated. Currently, this theme has been discussed in the most recent codes for Fiber-reinforced Concrete and its characterization.

The objective of quality control of fiber-reinforced concrete is to guarantee that pre-requisites set out by the design-engineer for the design of supporting structures are fulfilled. In addition to tests foreseen for mechanical characterization and characterization of the behaviour of fiber-reinforced concrete, which can be set out according to the type of support, all currently most complete and comprehensive codes for characterization of fiber-reinforced concrete, such as UNI 10834, EN 14721, EN 14488, foresee the execution of field tests to confirm homogeneity of the mixture with respect to the specified dosage for metal fibers.

Additionally, these codes suggest criteria for approval of the material.

As the most complete reference for quality control of fiber-reinforced concrete norm UNI10834 is to be found, followed by the recent EN 14487-1 integrating all previously explained concepts for qual-ity control of sprayed concrete.

Standard UNI10834, for what concerns fiber-reinforced concrete, proposes a classification of shotcrete by responsibility, and by levels of absorbed energy measured by punch testing on plate.

Table 5.21 - Table showing the type of fiber-reinforced concrete, following punch test on plate, UNI10834.

Class Deformation energy absorbedup to a point of 25 mm (J)

a

b

c

d

< 500

> 500

> 700

> 1000

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where:D

f : is the fiber dosage.

Mf: is the weight of the fibers contained in the sample expressed in kg.

Mc: is the weight of concrete of the sample.

Pm: is the volumetric mass of concrete expressed in kg over a cubic metre of concrete.

This equation is currently applied by any current standard norm to determine the mass ratio of metallic fibers contained into a concrete mixture of any type.

In order to provide an example of the process, a sequence of photos dealing with the process is shown hereinafter:

After having proposed a classification of the type of concrete following plate testing, quality control of the mixture is proposed, which begins by determination of the fiber content of the mixture. Testing is based on separation of the fibers embedded in a representative sample of fresh or of hardened mate-rial having a weight not below 5÷6 kg. After washing, the weight ratio is calculated following:

Table 5.22 - Table showing the functional classification of fiber-reinforced concrete, as proposed by UNI10834.

- Foundations- Fillings- Protection of temporary slopes- Surface protection- Protection of excavation surfaces in

- Single-shell structures- Repairs, restorations and tunnels linings

- Bypass tunnels- Piers- Surface protection- Protection of excavation surfaces in

- Fillings- Protection of slopes- Waterproofing

Use examplesAcronym

TN

PS

TS

PN

Destination of use

Non-structural

Structural

Structural

Non-structural

Temporary

Permanent

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Photo 5.23 - Weighing of the mixture in the mould.

Photo 5.24 - Extraction of the fibers by means of a magnetic element towards their subsequent weighing and calculation of the mass ratio as proposed by the equation in the norm.

Photo 5.19 - Manual addition of fibers to the aggregates which are transported to the mixing machine at the cement mixing station

Photo 5.20 - Appearance of the ready mixture in the fresh condition, to be noted the presence of fibers without agglomerations or any kind of problem related to inhomogeneity.

Photo 5.21 - Placement of the fresh mixture in moulds of calibrated weight.

Photo 5.22 - Beginning of the washing operation of the mixture to obtain the mass of fibers contained in it.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.24 - Table providing ductility indexes as proposed by code UNI 11039.

Ductility classes

Ds0 Ds1 Ds2 DP DHo DH1 DH2

D0

Ductility indexes(minimum

characteristic values)

D1

1)

0,3>

>0,5

0,5>

>0,7

0,7>

>0,9

0,9>

>1,1

1,1>

>1,3

1,3> 2)

>1,55

1,55> 2)

Softening behaviour Plastic behaviour Hardening behaviour

1) Values of ductility index D0 < 0,5 are typical of non-reinforced concretes withsteel fibers.2) Classes DH1 and DH2 of index D1 are characteristic of SFRC of highestperformance, which formulation requires the use of appropriately dosed specialfibrous reinforcements and of ad hoc designed base concretes.

Recently, the European standard EN 14487-1 has been approved, which considers control and prepa-ration of sprayed concrete. This is the first complete proposition comprising all the concepts proposed in previous sections. It proposes in a consecutive way, the following definitions.

As a first instance, it delimitates the characteristics of the material by means of bending tests as well as plate probes.

Table 5.23 - Table providing suggested testing sequences as proposed by the code UNI10834.

The standard UNI10834 does not deal with bending tests. For that, the norm UNI 11039 exists, of which it has been widely discussed within chapter 3, and where material characteristics are defined by means of results of bending tests. This norm proposes a classification of the material by means of ductility indexes.

Compressive strength

Initial strength

Fiber content (***)and additives dosage

Thickness

1.000 m1/month

(**)

(**)

400 m

3

2

1.000 m1/month

(**)

(**)

400 m

3

2

(**)

(**)

(**)

400 m2

400 m1/week2

3

00 m2/week400 m1/week

400 m

3

3

2

400 m1/

(**)

3

week

400 m1/week

200 m

3

2

1000 m1/month4

3

00 m1/semana1000 m1/month

400 m

3

3

2

200 m2/2

3

week00 m

2/week1000 m1/week

400 m

3

3

2

400 m1/4

3

week00 m

1/week400 m1/week

400 m

3

3

2

Test

Temporarynon-structural

Temporarystructural

Permanentnon-structural

Permanentstructural

Initial (*) At steadystate Initial (*) At steady

state Initial (*) At steadystate Initial (*) At steady

state

(*) A sample is considered as initial up to 15 samplings.(**) Upon request.(***) In fiber-reinforced concrete.Nota: If it is intended to make reference to the m2 put in place, an conventional thickness of 20 cm should be assumed.

Norm UNI 10834 foresees quality control of concrete in working conditions, beginning with the determination of the fiber content, and proposing a first testing sequence following the functional classification set out before. The case of testing of energy absorption is left open in order to be de-fined by the responsible of the project. The reference is provided hereinafter:

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.25 - Table providing levels of residual stress for fiber-reinforced concrete obtained by means of bending tests following EN 14487-1.

Table 5.26 - Table providing classification of fiber-reinforced concretes following their response to testing of the absorbed energy on rectangular plate (EFNARC) EN 14487-1

Strength level (minimum strength, MPa)Deformation range

Deflection(mm)

0,5–10,5–20,5–4

D1D2D3

S1 S2 S3 S4

1 2 3 4

Energy absorption class

E500

E700

E1000

Energy absorption in Jfor deflection up to 25 mm

500

700

1000

After having defined mechanical requirements for the material, the norm EN 14487-1 defines speci-fications for the materials composing the mixture.

Table 5.27 - Table providing materials specifications for the preparation of the mixture following instructions laid out in EN 14487-1

Requirements and test methodsComponent

Use of cement

Use of aggregates

Use of admixtures

Use of additions

Chloride content

Water/cement ratio

Use of fibers

The type of cement shall be specified, taking into account the influence ofcurrent temperature and heat evaluation on requiredworkability time, therequirement on strength development and final strength as well as thecurrent conditions. If required, it shall be checked by means of anappropriatemethod.

For permanent structures, the environmental conditions to which thesprayed concrete is exposed shall be in accordance with EN 206-1, aswell as precautions regarding resistance to alkaki-silica reactionsaccording toEN206-1.

Precautions regarding resistance to alkaki-silica reactions according toEN206-1 shall be applied.

Limitations for the use of admixtures set out in EN 934-2 and prEN 934-5shall not be exceeded.

The use of additions for permanent structures shall conform toEN206-1.

The chloride content of a sprayed concrete for permanent structure shallnot exceed the values given in EN 206-1, table 10 for the specified class.For steel fiber reinforced sprayed concrete, values for steelreinforcement apply.

For permanent structures, the environmental conditions to which thesprayed concrete is exposed shall be in concordancewithEN206-1.

Where water/cement ratio of a wet mix is specified, it shall be calculatedaccording toEN206-1.

Steel and polymer fibers shall comply to prEN 14889-1 and prEN 14889-2, other types of fibers shall comply to clause 5.1.1 of this standard.Fibers shall be added in such a way that a homogeneous distribution isobtained.

For fiber reinforced concrete

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

After having defined requirements for materials composing the mixture following due specifications, the norm EN 14487-1 provides recommendations for quality control of the same components in the fresh mixture, by foreseeing the determination of the fiber content set out in the mixture, as shown hereinafter:

Table 5.28 - Table providing recommendations for determination of consistence and density of materials in fresh concrete following EN 14487-1, determination of fiber content in the mixture.

Requirements and test methods

The density shall be determined in accordance with EN 12350-6

Fiber content shall be determined from a fresh sample according to prEN 14488-7

The sample shall be taken from in situ material unless otherwise specified

Property

Density

Fiber content

Table 5.29 - Table for determination of mixture properties in the hardened condition, comprehending the same mechanical properties as set out in EN 14487-1.

Once the content of the mixture and its density in the fresh condition have been determined, the norm EN 14487-1 provides recommendations for control and determination of the mixture properties in the hardened condition. These foresee the assessment of mechanical characteristics of the material as set out in the following table:

Requirements and test methods

An estimate of the early compressive strength can be determined in accordance withprEN14488-2.

The compressive strength of sprayed concrete is expressed and defined according to EN206-1. The strength shall be determined from tests carried out at 28 days in accordance with EN12504-1 on drilled cores, taken from the sprayed concrete structure according to EN 12504-1,or from sprayed panels according to prEN 14488-1. Their minimum diameter shall be 50 mmand the heigth/diameter ratio shall be either 1,0 or 2,0 specimen shall be tested in accordancewithEN12504-1.NOTE:The length/diameter ratio should be:- 2,0 if the strength result is to be compared to cylinder strength- 1,0 if the strength result is to be compared to cube strength

Thedensity of hardened concrete shall be determined in accordancewith 12390-7.

The modulus of elasticity in compression shall be determined in accordance with ISO 6784,except in repair applicationwhereEN13412 shall apply.

The flexural strength shall be determined in accordance with prEN 12390-5 for sprayedconcrete without fibers unless it is to be compared to fiber reinforced sprayed concrete whenprEN14488-3 shall be used.

The resistance to water penetration shall be determined in accordance with EN 12390-8. Thedepth of an in situ samplemay be reducedwhere the layer thickness is less than 150mm. Thedepth shall be sufficient to ensure that complete penetration does not occur. In addition thedirection of water penetration and the method of surface preparation shall be specified. Themaximumvalue of penetration shall be 50mm.The test is normally perfomedat 28 days.

Note: while a European test method is not available, reference should be made to nationalstandards.

The bond strength shall be determined for repair materials in accordance with EN 1542 withthe exception of mould size which shall not be smaller than 500 mm x 500 mm to provide aborder of at least 100mm in order to exclude defectivematerial in the edges of the specimens.Surface finish shall either be troweledwhenwet or groundwhen hardened otherwise it shall beon drilled cores in accordancewith prEN14488-4.

The first peak flexural strength shall be expressed as the average value of the strength at themoment of first peak determined in accordance with prEN 14488-3. The test shall normally beperformedat 28 days.

The ultimate flexural strength of fiber reinforced sprayed concrete shall be expressed aswhen determined according to prEN 14488-3. Unless otherwise required, tests shall normallybe performedat 28 days.

f0

The residual strength class of fiber reinforced concrete shall be determined for a specifieddeformation level. The stress-deflection curve shall be determined in accordance with prEN14488-3. The test is normally done at 28 days.

The fiber content shall be determined from a hardened sample in accordance with prEN14488-7,when it is not practical to determine it from the fresh sprayed concrete.The sample shall be taken from in-situmaterial unless otherwise specified.

The energy absorption capacity shall be expressed as the average energy absorptioncapacity, determined in accordance to prEN 14488-5. The specified energy absorptioncapacity for the required class shallmeet the requirements in table 3. The test is normally doneat 28 days.

Property

Early age strength

Compressivestrength

Density

Modulus of elasticity

Flexural strength

Resistance towater penetration

Freeze/thawresistance

Bond strengthto substrate

For fiber refinforced sprayed concrete

First peakflexural strength

Ultimate flexuralstrength

Residual strength

Fiber content

Energy absorptioncapacity

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.30 - Proposition for determination of the mixture’s properties preliminary to the work following EN 14487-1

In the same norm, procedures for quality controls during the course of the work are proposed.

Table 5.31 - Proposition for verification of materials received at the construction site following pr ENI 14487.

By interpreting the philosophy of underground works, the norm EN 14487-1 defines test methods preliminary to construction, in order to verify prerequisites set out in the design of the work following functionality concepts proposed by the norm itself, which consider what had been explained at the beginning of this chapter, and what is explained hereinafter as well:

Type of work:Inspection categoryPropertyConsistence for wet mixEarly age strength developmentCompressive strengthModulus of elasticityBond to substractUltimate flexural strengthFirst peak flexural strengthResidual strengthEnergy absorption capacity

Freeze/thaw resistance(with or without deicing salts)

Resistance to water penetrationCompositionFiber contentMaximum chloride content

Repair and upgrading Free standing structures Strengthening of ground1 32 1 32 1 32

Material

7

8

9

10

11

12

Test for density forliquid admixturesaccording to ISO 758

Inspection ofdelivery ticket

Test for densityaccording to ISO 758

Test according toEN 1008

Inspection of length,diameter and shapeaccording to prEN14889-1 and prEN14889-2

For comparison withmanufacturer´s statedvalue

To ascertain if theconsignment is asordered and from thecorrect source

To ascertain uniformity

To ascertain that the wateris free from harmfulconstituents

To ascertain if theconsignment is asordered and from thecorrect source

In case of doubt

Each delivery

Each delivery

If the water is notpotable; whennewsource isused for first time;and in case ofdoubt

Each delivery

Category1 Category 2 Category 3

Min sampling frequencyInspection/test Purpose

a

b

The delivery ticket or the product data sheet shall also contain information on the maximum chloride content andshould identify classification with respect to alkali silica reaction in accordance with the provisions valid in the place ofuse of the concrete. The delivery ticket shall contain or be accompanied by a declaration or certificate of conformity asrequired in the relevant standard or specification.

It is recommended that samples are taken at each delivery and stored.

Additionsbulk powder

Additions insuspension

Water

Fibers

Inspection ofdelivery ticket

To ascertain if theconsignment is asordered and from thecorrect source

Each delivery

-

-

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.32 - Proposition for determination of in situ mixture’s properties following ENI 14487-1.

Altogether, a routine procedure is indicated setting out test methods for quality control of the work to comply with its classification.

Table 5.33 - Proposition for routine tests following the work’s function category as set out in pr EB 14487-1.

Type of test

1

2

3

4

Test according toEN 12350-2 orEN 12350-5

Record of thequantity added

To assess conformity withrequired class of consistenceand to check possible changesof water content

To check the content

At start of production

Optional Every batch

Optional Every batch

Every batch

Category 1 Category 2 Category 3Min sampling frequency

Consistencewhen usingwet-mix method

Admixturecontent exceptaccelerator

Additionscontent

Fiber content

Inspection/test Purpose

Record of thequantity added

Record of thequantity added

To check the content

To check the content

Category 1 Category 2 Category 3

Free standing structures

Category 1 Category 2 Category 3

Reapir and upgrading

Category 1 Category 2 Category 3

Strengthening of ground

Control of fresh concrete1

2

3

Control of hardened concrete4

5

6

7

8

9

Control of fiber reinforced sprayed concrete10

11

12

13

Type of test

By calculationor by testmethod

According toprEN 14488-7

prEN 14488-2

EN 12504-1

EN 12390-7

EN 12390-8

See note d

prEN 14488-4EN 1542

a

b

prEN 14488-7

prEN 14488-3ouprEN 14488-5

prEN 14488-3

prEN 14488-3

Inspection/test

according to

min 1

1/5000 mor /months

2

12

1/1 000 mor1/5 000 m

3

2

When testing residual strength or energyabsorption capacity

1/2000 m or1/10000 m

3

2

1/200 m or1/1 000 m

3

2

1/2500 mor 1/month

2

1/500 m or1/2500 m

3

2

1/2500 m2

1/400 m or1/2000 m

3

2

Daily

Daily

1/100 m or1/500 m

3

2

1/250 m or2/month

2

1/250 m or1/1250 m

3

2

1/1250 m2

1/1250 m1/500 m

2

2

min 1

1/500 m or1/2500 mor min 1

3

2

1/1000 mor min 1

2

1/1000 mor min 1

2

1/1000 mor min 1

2

Min 11/2000 mor min 2

2

1/500 m ormin 2

2

1/500 m ormin 2

2

1/500 m ormin 2

2

1/100 m or1/500 ormin 2

3

1/500 mmin 2

2 1/200 m or1/1000 mor min 1

3

2

1/500 m or1/2500 mor min 1

3

2

1/1000 mor min 1

2

1/1000 mor min 1

2

Min 1

1/100 m or1/500 m ormin 2

3

2

1/100 m or1/500 ormin 2

3

1/500 m ormin 2

2

1/500 m or2

min 2

1/2000 mor min 2

2

Daily

Daily

1/50 m or1/250 mor min 3

3

2

1/50 m or1/250 ormin 3

3

1/250 m ormin 3

2

1/250 m ormin 3

2

1/500 mor min 3

2

Minimum sampling frequency

Water/cementratio of freshconcrete whenusing wet mixmethodAccelerator

fiber contentin the freshconcrete

Strength testof youngsprayedconcreteCompressivestrength

Density ofhardenedconcrete

Resistanceto waterpenetration

Freeze/thawresistance

Bondstrength

fiber contentof hardenedconcreteResidualstrength orenergyabsorptioncapacityUltimateflexuralstrengthFirst peakflexuralstrength

Daily

Daily

1/250 m ormin 3

3

1/50 m or1/250 ormin 3

3

1/250 m ormin 3

2

1/250 m ormin 3

2

1/250 m ormin 3

2

1/500 m2

or min 3

From recordof the quantityadded

When testing compressive strengthWhen testing compressive strength When testing compressive strength

When testing residual strength When testing residual strength

When testing residual strength

When testing residual strength

When testing residual strength

When testing residual strength

When testing residual strength

When testing residual strength

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133

5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Work’s function categories are suggested by the norm EN 14487-1 as indicated in the following reference tables:

Table 5.34 - Functional characteristics of repair works or construction of structures with moderate loading requirements following EN 14487-1.

Structures with low durability requirements and without risk for users and local residents,such as:- Construction in un-urbanized zones and far-off traffic ways-Temporary repairs in low risk situation

Structures and components with moderate durability requirements and with moderate risksfor users and local residents, such as:- Small buildings, houses- Sewers inmediumsized urban areas

Structures and components with high durability requirements and with high risks for usersand local residents, such as:- Rail or road tunnelswith heavy traffic- Factories classified as high risk, hospitals, schools

Example of inspection categoriesCategory

1

2

3

Table 5.35 - Functional characteristics of works with high loading requirements following EN 14487-1.

Structures and components with normal design complexity regarding risk of instability orfuncional safety andwith low risks for users and local residents such as:- Sewers in small urban zones-Tunnels, bridges and other structural light traffic circulation- Permanent stabilisation os slopes

Structures and components with special design complexity regarding risk of structuralinstability or functional safety as well as high durability requirements and with medium to highlevel of risk for users and local residents, such as:- Rail or road tunnelswithmedium traffic-Aqueducts for drinkingwater- Small dams, sewers inmediumsize urban areas, canals- Hospitals, schools and high occupancy buildings

Examples of inspetion categoriesCategory

2

3

Constructions with minor degree of risk in design and structural instability as well as lowdurability requirements, usually constructions with short design life and low risk of structuralinstability, such as:- Small permanent constructions- Stabilisation for small or temporary slopes or pits

Constructions with normal design complexity regarding risk of structural instability orfunctional safety as well as constructions with moderate durability requirements/design life,such as:- Permanent stabilisation of slopes-Temporary sprayed concrete for tunnels and caverns in poor ground

Constructions with special design complexity regarding risk of structural instability orfunctional safety as well as constructions with high durability requirements/long design life,such as:- Caverns in very poor ground-Tunnels for traffic

Example of inspection categoriesCategory

1

3

2

Table 5.36 - Functional characteristics of constructions with high loading requirements for underground works following EN 14487-1.

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5. Applications of fiber-reinforced concrete: tunnels, design of the pre-lining and of the final lining.

Table 5.37 - Functional characteristics of self-supporting constructions with high loading requirements following EN 14487-1.

It is important to clarify that the norm EN 14487-1 provides classifications not only for the use of sprayed concretes to be applied for underground works; the norm describes as well other types of works following their functionality.

5.7 - Current standard situation.

Referring to the normative situation for underground works, it may be concluded that the combi-nation of the complete set of norms already described within chapter 2 concerning classification of fibers, within chapter 3 concerning characterization of fiber-reinforced concrete, and within the present chapter concerning quality control of fiber-reinforced concrete for underground works, is globally sufficient in order to obtain proper specifications for a design integrating the technology of fiber-reinforced concrete.

In the past years a number of standards have been developed which objective is to clarify that fiber-reinforced concrete is a complex theme depending from many factors such as:

- the type of fibers - the quality of concrete - the structural responsibility and functionality of the work - the mechanical characterization of the material

By highlighting that most complete standards laid down up to now which include these concepts, depart from the selection of materials, their characterization, and the consideration of structural criteria for the design and control of the work, one can find:

Constructions with minor degree of risk in design and structural instability as well as lowdurability requirements, usually constructions with short design life and low risk of structuralinstability, such as:- Decorative imitation rock- Surroundingwalls

Constructions with normal design complexity regarding risk of structural instability orfunctional safety as well as constructions with moderate durability requirements and low risksfor users and local residents, such as:-Open-top arqueducts or canals- Small swimming pools- Decorative imitation rock or sculpture

Constructions with special design complexity regarding risk of structural instability orfunctional safety as well as constructions with high durability requirements and high risks forusers and local residents, such as:- Small business, houses-Domesand shells- Fire protection for steel structures- Large swimming pool- Security structures-High imitation rock receiving public- High climblingwalls

Category

1

3

2

Example of inspection categories

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EN 14487-1 Sprayed Concrete — Part 1: Definitions, Specifications and Conformity. This norm is coherent with Eurocodes, managing to cover comprehensively criteria for the selection and quality control of the material.

Referring to the level of criteria for structural design, one can find:

CNR - 25 - Istruzioni per la Progettazione, l’Esecuzione ed il controllo di Strutture realizzate con Calcestruzzo Fibrorinforzato. (Instructions for design, execution and control of structures made of fiber-reinforced concrete) This being the most complete norm concerning the design of structures made of fiber-reinforced concrete.

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The industrial, harbour, airport, road pavements and further ones, are technically considered as plates resting on the soil subjected to punctual, distributed or constant loads and are traditionally reinforced to shrinking and temperature, and, moreover, may be reinforced to bending when the load level needs it. There are cases where the floor design doesn’t provide for any reinforcement, as for pedestrian floorings and parking areas.

The mechanical behaviour of the plates resting on the soil, through the different kinds of loads to which they may be subjected, is compatible with the level of resistant strains which may be produced by fiber reinforced concrete.

The technology of fiber reinforced concrete has reached a very important technical level, as in the last decade, the methods of analysis and the behaviour of the material have been developed for the correct modelling of the appliances, causing a substantial increase of the appliances achieved with this technology, and the development of research and regulations for the design which mark out the structural responsibility of this new material.

In the following paragraphs of this chapter there will be explained in detail the technical possibilities offered by the technology of fiber reinforced concrete in comparison with the existing traditional methodologies.

6.1 - Industrial, harbour, airport, road, and special uses.

Photo 6.1 - Example of use in the airports. Photo 6.2 - Example of use in the parking areas.

Photo 6.3 - Example of use in industrial flooring. Photo 6.4 - Example of use in the ports.

6. Appliances in fiber reinforced concrete. Floors design.

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6. Appliances in fiber reinforced concrete. Floors design.

Nowadays the normative codes refer to a methodology of calculation for the not reinforced concrete based on Westergaard theory, in which a rigid plate resting on the soil is considered, and where it’s determined the thickness of the plate through the modulus of relative rigidity in function of the bearing capacity of the soil. This methodology has been exposed by ACI 360R – Design of Slabs-on-Ground, through the following available methods:

- WRI (Wire Reinforced Institute). - PCA (Portland Cement Association). - COE (Corp of Engineers). - PTI (Post Tensioning Institute). - ACI223 (shrinkage compensating institute).

The resistant capacity to determine the thickness of the plate is just committed to the Bending resistance or Concrete Modulus of Cracking (MOR). The only exception is the PTI method, which exploits the post-stretched and pre-stretched technology to increase its load capacity, as this is an option for plates where soils have a poor and unstable bearing capacity, or for structural solutions. Consequently there are plates which require bending reinforcement, for load reasons, in which the design conventional criterium for reinforced concrete is applied.

The basic principle which differentiates the design criterium from the methods previously mentioned, in which the responsibility to bending is only based on the concrete modulus of cracking, is based on the applied safety factors.

In all methods it’s applied the concept of state in service of concrete as resistant material, minimizing its risk, decreasing its capacity through a safety factor which may vary from a minimum of 1.7 up to a maximum which may fluctuate from 3.9 to 4, according to the following effects:

- Modulus of cracking radium, for the bending strain tension. - Influence of shrinkage strains. - Number of loads repetition. - Material fatigue and impact.

6.2 - Methodology of conventional design for floors.

CTODCTOD0

Load

Pmax

P Pmáx available for thecalculation of Mr of project,in the conventional concrete

máx

Minimum FS = 1.7 forthe ordinary concrete

Behavior of the ordinary concrete

Graphic 6.1 - Exemplification of the minimum service level for design in simple concrete. Bending test to determine the material MOR.

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Classification of plates proposed by ACI 360R – Design of Slabs-on-Ground.

In order to be more precise on the alternative of plates resting on the soil, ACI 360R – Design of Slabs-on-Ground, mentions the possibility of designing the six following cases:

A. Plates in simple concrete. In this kind of plates the design of thickness is based on simple con-crete bending capacity (Modulus of cracking – MOR), where the element is considered not to arrive at cracking and not to need any reinforcement. The loads and the quality of material have a safety factor to assure the usable life condition before generating the cracking. They are floors where the joints spacings are quite narrow.

B. Plates reinforced for shrinkage and for temperature effects. The design conditions are the same as those arranged for plates without reinforcement, but in this case a reinforcement is added to control shrinkage and thermic effects; the reinforcement is allocated in the third superior of thickness of the element, where there is the resultant of the strains triangular diagram. The distance between the joints may be enlarged according to the equation “Sub Grade Equation”, which will be illustrated afterwards.

C. Plates in compensated contraction concrete with shrinkage reinforcement. In this case plates are produced with compensated contraction concrete. The plates are shrinkage reinforced in the third superior, and the thickness measurement is based totally on concrete bending capacity, as in cases A and B.

D. Shrinkage post-stretched plates. As it can be inferred by the name, they are plates which will be post-stretched to face the shrinkage and temperature effect, as it’s possible that large joints spacings are reached. The thickness premeasurement strictly follows the methodology used in the previous cases.

E. Plates post-stretched and reinforced with active pre-stretched ropes. They are designed for the condition of not cracking, where the pre-stretched ropes allow to optimize the plates thickness, and the post-stretched ones allow to control the shrinkage effects. These plates may be designed as independent systems of attics, of wide spans, for the case of low capacity soils, where the solution of resting plate becomes a structural attic, which will convey the loads to a system of deep founda-tions. The PTI has got all the methodology for the design of these plates which differentiates from those previously mentioned.

F. Reinforced plates for structural actions. Unlike the cases mentioned above, the design methodol-ogy of this kind of plates implies cracking as a mechanism which activates the established strain, and the design is made real through the conventional methodologies of reinforced concrete, in which the bending strains to which the plate is subjected require a conventional reinforcement, both in one and double common bars mesh, and in welded wire mesh.

Nowadays the available design methodologies, provided and described in ACI 360 R and previously mentioned, are considered valid; here follows a correspondence of provided design methodologies in function of the typologies of floor plates described:

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6. Appliances in fiber reinforced concrete. Floors design.

Project method

PCA WRI COE PTI ACI223

Type of project action

Thickness designType A.

Plates in plain concreteRelated details, joints

Thickness designType B.

Reinforced plates for shrinkage

and temperature effect Related details, joints

Thickness designType C.

Related details, joints

Thickness designType D.

Plates prestressed for retractionRelated details, joints

Thickness designType E.

Related details, joints

Thickness designTipo F.

Related details, joints

Plates in concrete for

contraction compensated with

retraction shrinkageo

Plates prestressed and

reinforced with prestressed

active cables

Plates reinforced for

structural actions

Type of construction

Table 6.1 - Types of design methods in function of the floor type. Reference ACI 360-R.

Characteristics of the foundation.

In the design of plates resting on the soil, a factor of great importance for the design is the condition of the supporting soil. In all design methods previously commented it’s necessary to propose a stable condition of the soil, which will have to be guaranteed for the framework usable life.

Most of the bibliography on the subject expresses the condition of the soil with two basic expressions highly used in geotechnical environment, such as:

- Soil Modulus of Reaction. - California Bearing Ratio (CBR).

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6. Appliances in fiber reinforced concrete. Floors design

Table 6.2 - Schedule of the types soil in function of CBR and Vertical Reaction Modulus. Reference ACI 360-R.

In all designs the improvement of the foundation which will have to hold the framework is recom-mended. For this improvement, it’s advisable to use at least a layer of granular selected material well assorted of about 30 – 40 cm which, in combination with the foundation soil, may reach a modulus of vertical reaction or CBR, which offers a good safety factor to the framework and minimizes the risk. There are situations in which the improvement must be more severe, including the removal of shims of the soil, which have to be replaced by selected material, and cases when reinforcement geosyntethics are used, always with the aim of generating a stable value of the soil condition which may be guaranteed during the framework usable life.

Definitions of loads for the design of plates resting on the soil.

The load conditions more commonly used in the design of plates resting on the soil, are the follow-ing:

- Vehicular wheels loads: trucks, montacarichi, planes, etc. - Concentrated loads, such as shelves, equippings supports, etc. - Equippings line or load strip, assorted goods, etc. - Uniformly distributed load. Materials resting directly on the floor. - Load in the structural phase. Support of equippings necessary for the floor manifacture. - Environment effects (temperature effects) including the case of expansive soils. - Extraordinary loads. Any special event which may cause a remarkable effect on the plate.

They have to be considered all important and, under the ingegneristico point of view, in every design it’ll be necessary to start the respective analysis to determine the most unfavourable case, which will lead in the framework. In consequence of the experience, the concentred loads, shelves, equippings,

Here is following a correlation between the two expressions:

2 3 4 5 6 7 8 9 10 15 20 26 30 40 50 60 70 80 90(BCS 314) California Bearing Ration 'CBR' (%)

Standard modulus of soil reaction K (MPa/m) (Placa de 30" = 76 cm)

7.5 15 20 25 35 40 50 55 70 80 95 115 130 135 155 165

G = GravelS = SandM = SiltC = ClayW = Well gradedP = Poorly gradedU = Uniformly gradedL = Low to medium compressibilityH = High compressibilityO = Organic

GWGM

GPGU

GC

SWSM

SPSUSC

CLML

CLML

OL OL

MHMHCHCH

OH OH

LegendCompacted densitiesNatural densities

NOTE: The value of k is extracted of the abacus for each type of soil, especially for groups L and H, would have to coincide with the inferior limit of the interval of corresponding values.

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vehicular loads, are the most demanding for these frameworks and the area on which they stand affects substantially the effect that they produce in terms of plate stress.

Here are following as example some valid relations between the contact surfaces and the kinds of concentred loads.

Table 6.3 - Project considerations in function of the type of load.

Type of load

Concentrated loadsDistributed loads

Posts of storage racksWith

base platesWithout

base plates Storage areas

Special loads

Considerations of project- Negative moment inuloaded area

- Joint faulting- Settement

- Concrete bearing- Punching shear

- Flexural stress under load

Vehicle wheelsSolid SpecialPneumatic

2 4 10 20 40 100 200 400 100010 20 40 100 200 400Square inches Square feet

Load contact area(for each tire, post, os single loaded area)

Safety factors.

The safety factors for the design of plates resting on the soil, as for all frameworks, are defined by the national technical regulations and, in Europe, by the EuroCodes.

In various Countries, for instance in France and in Italy, there are specific regulations for the design, construction and testing of industrial floors.

A distinction has to be made between the safety factors on loads and those on the material.

In the case of concrete, in Europe it’s used a safety factor equal to 1 for the control at SLS, and 1,5 for SLU. In the case of loads a distinction between cyclical and static loads has to be made: in every Country there are different values. In any case, it’s necessary to provide more and more increasing safety factors for more and more important numbers of load cycles.

The safety factors defined for the design may be of a minimum of 1.4 and may arrive at factors of 3.9 – 4.8 in function of the use.

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Design methods.

As it has been mentioned before, the available plan methods assume that concrete doesn’t have any reinforcement and that its capacity resistant to bending (modulus of cracking), to be used for the framework design. In most methods the use of reinforcement is required only to assure a joints wider spacing and for checking the effects of shrinkage and thermic variations.

For the thickness measuring of a plate framework resting on the soil there are three of the methods shown at the beginning of the chapter. There follows a description of some of the important differ-ences between them.

Portland Cement Association Method (PCA).

This method has been developed on the basis of Pickett’s analyses, where there are included variables such as the stressing tension due to loads, the capacity resistant to concrete bending, the contact area and the loads spacing, and the modulus of reaction of soil. The method uses abacuses which include the variables mentioned before for the definition of thicknesses. The work is always done considering the not cracked condition of concrete. The cases of wheel loads, concentred loads, uniform loads are considered. Temporary loads are not considered.

To continue there are shown some examples of the graphics used for the different kinds of loads, the initial condition for all graphics is equivalent to the work strain, which will be determined in function of the capacity to concrete bending, decreased by a safety factor which will have to be selected by the designer, according to the regulations in force:

Table 6.4 - Minimum safety factors for loads effects recommended by ACI 360-R.

Load type Commonly usedfactors of safety

Occasionally usedfactors of safety

Moving wheel loads 1,7 to 2,0 1,4 to 2,0+

Concentrated (rackand post) loads 1,7 to 2,0 Higher under

special circunstances

Uniforme loads 1,7 to 2,0 1,4 is lower limite

Line and strip loads 1,7 2,0 is a conservativeupper limit*

Constructive loads 1,4 to 2,0 -

work

ACI 360R suggests safety factors in function of the kind of analysed loads, and doesn’t consider further factors.

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Figure 6.1 - Graphic example for the measuring of thickness for the case of wheel loads with simple axes, for different types of soil. PCA Method. Reference ACI 360-R.

where:s

work = work strain;

MR = concrete modulus of cracking;fs = safety factor.

Figure 6.2 - Graphic example for the measuring of thickness for the case of wheel loads with double axes, for one type of soil. Several curves for different values of soil capacity exist. PCA Method. Reference ACI 60-R.

For the case of distributed loads, the method PCA has got an abridgement of load capacities of plates resting on the soil in function of its bearing capacity, the concrete quality and the provided thickness of the plate.

Stre

ssper 1

000LB

axleload

(psi)

Wheel spacing(In.)

Effective contactarea (Sq. in.)

Slabthickness(In

.)

S

2550100200

30

4060

80

120

13

12

11

10

9

8

7

6

5

7 ¾

40

30

20

15

10987

6

5

4

3

S, D

ual w

heelspacing(In

.)d

Slab thickness(In.)

Effectivecontact area(sq. in.) F,

Equivalentload

factor

50

45

40

35

30

25

20

15

10

0.90

0.85

0.80

0.75

0.70

0.65

0.60

0.55

0.50

Sd

S

Sd

14

121085

20010050

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Table 6.5 - Abridgement schedule of the PCA Method for strains available in the plates design for several thickness, for the case of distributed loads. Reference ACI 360-R.

For the case of concentrated loads, as shelves could be, the machines foundations, or any kind of element which generates concentrated loads, the method has got some schedules for thickness measurings, in function of the contact surface, of the support load and of its orthogonal distribution. These schedules are generated for different levels of soil bearing capacity.

501002005010020050100200501002005010020050100200

5

6

8

10

12

14

Concrete flexural strength (psi)

535760107585883011756809601355760107015158301175166089512701795

5505858301175640905128074010451480830117016559051280181098013851960

6006359001270750105514958651220172586513651930105514952115114016152285

6506859651370750105514958651220172596513651930105514952115114016152285

700

Allowable load (psf )(2)Slabthickness(In.)

Subgradek (pci)(1)

Stress

per 1

000LB

postload

(PSI)

Slab

thickness(In

.)

Subgrade K = 50 pci

Effective contact area(Sq. In.)

8070

60

50

40

30

20

15

10

80 40 20 10

14

13

12

11

10

9

8

7

6

5

4060

100x. In.

4060100y. In.

4010060

Figure 6.3 - Schedule of abridgement of the method PCA for thickness measuring of plates with concentrated loads. Reference ACI 360 R.

The method has all the same produced an abridgement for the case of distributed loads, in which limitations for joints spacing are mentioned.

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Table 6.6 - Schedule of abridgement of the method PCA for strains available in the design of plates of different thickness. For distributed loads, it provides for joints spacing. Reference ACI 360R.

5

6

8

10

12

14

5

6

8

10

12

14

5

6

8

10

12

14

Subgrade k = 50 pci (3)

Slabthickness(In.)

Workingstress(psi)

Criticalaislewidth(ft.)(2)

Allowable load (psf)At criticalaislewidth

At other aisle widths6 ft.aisle

8 ft.aisle

10 ft.aisle

12 ft.aisle

14 ft.aisle

Subgrade k = 100 pci (3)

Subgrade k = 200 pci (3)

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Method Wire Reinforced Institute: This method, like PCA, assumes as condition concrete without reinforcement, considering as resistant capacity the concrete modulus of cracking. Very similar to PCA method, it proposes curves and schedules for the measuring of shims for the cases of loads of wheel axes, uniformly distributed loads, it doesn’t provide for concentrated loads, nor variable loads in the constructive phase.

For the case of loads for wheel axes, starting from known conditions, as the concrete bending strength, which is already reduced for the assumed safety factor, wheel loads and axes separation, concrete modulus of elasticity and foundation strength, they are applied in consequent graphics that from a given thickness, determine the “parameter of relative strain”. Once determined such parameter, this is applied in other graphics, for the determination of the acting moment and, with it, it’s possible to go on with the final check graphic as, in function of the work bending strength of the material and of the design moment, the definitive thickness of the plate may be verified.

For the case of distributed loads the process is exactly alike, but, stating from the definition of the relative strain parameter, there are particular curves for the condition of uniformly distributed loads where in function of the preliminary joints spacing, the thickness can be determined.

The previously described graphics are shown below:

Figure 6.4 - Relation between plate thickness and relative strain parameter. Method WRI. Reference ACI 360-R.

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N- 2

65inch

(pou

nds/inch/kip)

Unitmom

ent -

1000

lbwh

eel(lb-In

. per

In.) Additiona

l unit m

omen

t(lb-In

. per

In.)

Add M = 16 inch ( inch/kip)pounds/

Distance between centersof load wheels (In.)

Equivalent loaded diameter (In.)Diameter = 5,0

Influence of otherloaded wheel

420

400

380

360

340

320

300

280

260

240

220

200

180

160

140

120

100

D/k = 3.4

0 5 10 15 20 25 30

100

80

60

40

20

040 50 60 70 80 90 100 110 12045

20010050

2010

2.5

200

100

50

20

10

2.5

D/k

30

150

Figure 6.5 - Graphic of design for wheel loads, in function of the relative strain parameter. Method WRI. Reference ACI 360-R.

Figure 6.6 - Graphic of design in function of the acting moment, definitive thickness measuring. Method WRI. Reference ACI 360-R.

Aisle width (In.)

Aisle width = 10 ft. = 120”

Tota

lsla

bm

om

ent(lb-f

t.per

ft.)

Uniform load(ksf)

Uniform load = 2500 psf = 2,5 ksf

Allow tension = 190 psi

Slab thickness (In.)

D/K = 3.4

Tota

lsla

bm

om

ent(lb-f

t.per

ft.)

H = 8”

4 6 8 10 12 14 16 1812,000

5,000

5,000

6,000

1,500

3,000

10,000

400

1,000

9,000

800

2,000

4,000

8,000

900

500

7,000

600700

4,000

3,000

2,000

1,500

1,000

6,000

900

7,000

800

8,000

700

9,000

600

10,000

500

11,000

400

300

40 60 80 100 120 140 160 180 200

10

7

543

21.5

1.0

0.7

0.50.40.3

0.2

0.15

0.10

0.07

0.05

D/K

1.0

2.3

5

10

20

50

100

150

250

500 400

300200

100

50

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Figure 6.7 - Graphic of design for distributed load, in function of the relative strain parameter and its relative design graphic of the definitive thickness. Method WRI. Reference ACI 360-R.

Corps of Engineers (COE) Method: This method bases its analyses on the resistant characteristic of not reinforced concrete, called Modulus of Cracking. The method determines relations for axis load conditions per wheel, defining “Design indexes” in function of the kind of load.

The method considers the strain produced in the intrados of the concrete section.

There are proposed curves in function of the “Design Index” and of the material bending capacity, in function of the bearing capacity of the supporting soil.

Table 6.7 - Schedule of “Design Index” in function of the load for axis types. Method COE, Reference ACI 360-R.

Capacity (lb)Design axle loadNo, of tiresType of tireTire contact area (sq. In.)Effective contact pressure (psi)Tire width (In.)Wheel spacing (In.)Aisle width (In.)Spacing between dual wheel tires (In.)

(lb)4000100004

Solid27.012563190--

6000150004

Solid36.120873390--

10000250006

Pneumatic62.51008

11.52.111323

16000360006

Pneumatic100909

13.58.131444

20000430006

Pneumatic119909

13.58.131444

520001200006

Pneumatic3169516

20.79.201924

Category I II III IV V VI

Aisle width (In.)

Aisle width = 10 ft. = 120”

Tota

lsla

bm

om

ent(lb-f

t.per

ft.)

Uniform load(ksf)

Uniform load = 2500 psf = 2,5 ksf

Allow tension = 190 psi

Slab thickness (In.)

D/K = 3.4

Tota

lsla

bm

om

ent(lb-f

t.per

ft.)

H = 8”

4 6 8 10 12 14 16 1812,000

5,000

5,000

6,000

1,500

3,000

10,000

400

1,000

9,000

800

2,000

4,000

8,000

900

500

7,000

600700

4,000

3,000

2,000

1,500

1,000

6,000

900

7,000

800

8,000

700

9,000

600

10,000

500

11,000

400

300

40 60 80 100 120 140 160 180 200

10

7

543

21.5

1.0

0.7

0.50.40.3

0.2

0.15

0.10

0.07

0.05

D/K

1.0

2.3

5

10

20

50

100

150

250

500 400

300200

100

50

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Figure 6.8 - Graphic of the thickness measuring in function of the “Design Index”, soil bearing capacity and concrete banding strain. Method COE, Reference ACI 360-R.

Post-stretched Plates (PTY) Post-stretched Attics (PTY)

The decision of using post-stretched floorings technology, arises generally from some simple reasons such as: - Systems which will be put on soils with very low support capacity and where the solution turns from solution of plate resting on the soil into a system of attics resting on elements of deep foundation, where it’s necessary a system of attic having a structural behaviour different from that of a plate resting on the soil. This system must be designed as a superstructure attic. - To obtain wide spans without joints. Being this case considered as a plate resting on the soil, the post-stress of the inferior part of the section has the aim of resisting the effects of shrinkage and temperature, as the bending design is carried out in the same way as it has already been explained for the previous methods, using the concrete bending capacity.As for post-stress methods, this handbook will not go into details. A good treatment can be found in ACI 360R. As for the design concept, the institution PTY has got in its publications all the options of design for this kind of elements.

Conventional design in reinforced concrete considering the elastic soil

As last alternative, the flooring plates can be bending designed through the conventional criteria of reinforced concrete, in which there are frameworks in the inferior part to generate a reinforced section capable of resisting the stresses caused by loads. The modulus of calculation will be that of an attic resting on an elastic soil according to the theory of plates. It would be very conservative to analyse the attic as a rectangular strip with a bending capacity. In order to develop suitably the calculation, it’s advisable to use programs to the finished elements which allow the plate spatial moulding and to mean the structural behaviour under basic aspects such as strain, distortions and breaking mechanisms.

Flexuralstrength(psi)

Design index= 10

Thickness(In.)

900

800

700

600

500

400

300

16

14

12

10

8

6

4

615

98765

4

3

2

1

K = 25 pci

100

50100

200300

400

500

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As example the following cases of loads for plates resting on the soil are shown:

Figure 6.9 - Example of concentrated loads in a plate resting on the soil. Figure 6.10 - Example of concentrated load at the centre of supported about the soil.

Figure 6.11 - Example of concentrated loads generated by a plane in a plate resting on the soil.

Here follow some cases of analysis of plates resting on the soil, with moulding to the finished ele-ments:

Figure 6.12- Example of a plate model FE, case of central load Figure 6.13 - Example of a plate model FE, case of central load in an extremity.

The loading area (mm2)

Fibers dosage (kg/m3)

Wing landing gear

Nose landing gear

Body landing gear

Fibers dosage (kg/m3)

LoadLoadPlate

Plate

Maximum value:

Maximum value:Minimum value:

Minimum value:

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Figure 6.14 - Example of a plate model FE, case of load in the plate corner. Figure 6.15 - Example of a plate model FE, case of distributed load.

6.3 - Design of joints in floors.

The design of joints in floors is a particularly important subject for the durability of such frame-works.

In various Countries there are Regulations or Recommendations of Good Practice, such as ACI 360R (USA), TR34 (United Kingdom), NF P 11-213 (France), UNI 11146 (Italy), which classify the different kinds of joints and establish the criteria for design and manifacture.

Here are listed the kinds of joints:

Shrinkage or control joints.

They are joints prepared for the control of concrete shrinkage, which are made by cutting the hardened concrete some hours after the flooring casting, normally between 6 and 8 hours after the casting. Its spacing will depend on the attic thickness and by the possible addition of a reinforcement. The joints can provide or not elements of interconnection between the plates, that will depend on the use destination.

Figure 6.16 - Example of cut control joint.

LoadLoad

PlatePlate

Maximum value:

Maximum value:Minimum value:

Minimum value:

Congrol jointArmor

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Photo 6.5 - Example of a control joint execution. Photo 6.6 - Example of a control joint.

Insulation joints.

As their name mean, they are joints made to insulate constructive elements which for the different rigidity may damage the plate. Such joints are provided before concrete casting.

Figure 6.17 - Example of insulation joint.

Photo 6.7 - Example of insulation joint. Photo 6.8 - Example of insulation joint already manufactured.

Construction joints.

It’s the joint which delimits the floor plates cast in different phases of the construction. Such ele-ments are to be planned so as to be compatible with the control joints modulation. This kind of joints provides for the interconnection between plates with mobile elements which allow the sliding of two adjacent plates.

Expanded poliestireneJoint filling

Form

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Armor Construction joint

smoot dowel steel bar

Figure 6.18 - Example of construction joint.

Photo 6.9 - Example of a construction joint. Photo 6.10 - Example of a construction joint already executed and the connection bars close-up.

Photo 6.11 - Connection bars arrangement in the construction joint. Photo 6.12 - Crossing between construction and control joints after casting.

Control joints measuring.

For control joints measuring there are several technical positions of different institutions. The control joint may be designed for two kinds of plates on soil:

Plate without reinforcement Type A (according to ACI 360 R).

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Table 6.8 - PCA recommendation for the control joints spacing for not reinforced plates. Recommended measures in ft (Feet). References ACI 360-R.

5 ''67''''

8 ''9 ''10 ''

101214161820

131518202324

151821242730

Slabthickness ''

Slumpless

than 4''.Aeggregat

< / ''.3 4

Aggregate> / ''.3 4

Slump 4 to 6 inches

Plates reinforced for shrinkage and temperature.

In order to space further the control joints, or when the temperature conditions to which the plate is subjected during its usable life are severe, all reference publications and institutions state to add a reinforcement going from a minimum quantity of 0.015% up to 0.03% of the section area in severe cases.

This reinforcement must be settled in the superior third of the thickness where there should be the resultant of the strain triangular diagram due to shrinkage and temperature

In this kind of plates, already described at the beginning of this chapter, the control joints measuring is based upon the behaviour of the plate subjected to plastic shrinkage. It’s advisable that the plate, rectangular or square, has similar dimensions, with ratio L

max / L

min ≤ 1.2. The basic rule in measuring

establishes:

where: L = spacing length; h = provided height of the plate.

The PCA (Portland Cement Association) recommends a very similar spacing the previous one, con-sidering the maximum dimension of aggregates and the mixture slump.

Figure 6.19 - Example of plate reinforced for shrinkage and temperature.

ArmorConcrete

soil

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The codes traditionally used for the design of floors on the soil without bending reinforcement, such as PCA (Portland Cement Association), WRI (Wire Reinforced Institute) and COE (Corp of Engineers), use, for steel measuring for temperature and shrinkage, the formula “Subgrade drag equation”:

where:A

s = Steel area in square inch per linear foot;

fs = Allowable strain of reinforcement steel in psi;F = Friction factor;L = Provided distance between joints;w = Weight of the plate in psf, considering 12.5 psf per inch of thickness.

With this formula it’s possible to verify how much a good spacing without the presence of reinforce-ment can be exploited.

The dimension of the plate will be subordinated to its feasibility, according to the load levels, being possible that the applied load can reduce its dimensions.

Compensated shrinkage concretes.

Compensated shrinkage concretes are the solution to the problem of control joints. These kinds of concretes are described in ACI 223. Their work mechanism is based upon concrete expansion in the first days, that later on will be compensated by shrinkage. It’s necessary a minimum reinforcement of 0.15%.

This technology allows to obtain control joints spacings wider than those previously explained. Nowadays, thanks to this possibility, there’s a trend towards solutions of floors with joints spacing wider than 15 m.

Curling (or bending) and Warping of the plate resting on the soil.

The phenomenon of bending or curling is common in not reinforced plates and consists of the an-gular distortion of the angles surface. Normally this phenomenon affects a radium from 2 to 5 feet, measured from the same edge. The phenomenon is due to the difference of water contents and temperature between the external and internal surfaces of the plate.

The Warping phenomenon, very similar to curling, coincides with the distortion of the surface in general, caused by internal strains generated by differences of steam or of temperature between the framework surfaces

Both phenomena can be controlled with a combination of control and construction joints, and with a suitable shrinkage reinforcement.

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Zone 2 Zone 2Zone 1

Zone 2 Zone 2Zone 1Figure 6.20 - Examples of bending of plates resting on the soil. Zone Nr.2 value is usually equivalent to a length from 2 to 5 feet.

6.4 - Methods of floors design in fiber reinforced concrete.

Fiber reinforced concrete is used in plates resting on the soil when the strains produced by loads on the framework are compatible with its mechanical behaviour.

As it has been explained in the chapter on the mechanical characterization of fiber reinforced con-crete, for the design of floors on the soil is exploited the bending mechanical property at the material last state. Having also an improvement of the cutting strength, in a tridimensional analysis of such frameworks, it’s possible to visualize the correct redistribution of the strains.

Fiber reinforced concrete, being a homogeneous material in its whole volume, offers a continuous strength in all directions to the actions which may take place and, in the particular case of flooring, this property can be exploited as much for the bending design, as for the shrinkage and temperature design.

Basically, the addition of fibers in concrete matrix, causes the change of the behaviour from fragile to ductile. In particular ductility allows to change the criterium of analysis of the material, passing from a service condition with safety factors for the material, to work with increased loads and to design at last state, only possible with ductile materials, getting as result a better possibility of exploiting the material resistant capacity.

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Graphic 6.2 - Example of bending test UNI 11039 to determine the bending capacity of the concrete.

Wirand fFibers c,cube=30 MPa

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 3.5

CTOD m (mm)

Plain concreteVf=0.38% (30 kg/m )3

Curves SFRC

2 2.5 3

Plain concretecurves

Nom

inalstress

N( M

Pa

(

Graphic 6.3 - Example of minimum service level for a plan concrete design. Bending test to determine the material resistant moment.

As it can be noticed, on the basis of the norm ACI 360 R, there is a minimum reduction of 42% of material resistant capacity, being a fragile material.

Using fiber reinforced concrete, it’s exploited the material last resistant characteristic as resistant capacity and opposing increased loads to it.

The minimum requirement for fiber reinforced concrete structural use consists of a residual strength ≥ 50% of first crack strength. The fiber reinforced concrete, depending on the quantity of reinforce-ment it has got, will have the possibility of being more exploited at a structural level and offering a resistant capacity equal or greater than the maximum one reached in service by plain concrete.

CTODCTOD0

LOAD

Pmax

Pmax available for thecalculation of the design Mr,in conventional concrete

Minimum FS=1.7 forplain concret

Plain concret behavior

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Graphic 6.2 - Example of bending test UNI 11039 to determine the bending capacity of the concrete.

Wirand fFibers c,cube=30 MPa

0

0.5

1

1.5

2

2.5

3

3.5

4

0 0.5 1 1.5 3.5

CTOD m (mm)

Plain concreteVf=0.38% (30 kg/m )3

Curves SFRC

2 2.5 3

Plain concretecurves

Nom

inalstress

N( M

Pa

(

Graphic 6.3 - Example of minimum service level for a plan concrete design. Bending test to determine the material resistant moment.

As it can be noticed, on the basis of the norm ACI 360 R, there is a minimum reduction of 42% of material resistant capacity, being a fragile material.

Using fiber reinforced concrete, it’s exploited the material last resistant characteristic as resistant capacity and opposing increased loads to it.

The minimum requirement for fiber reinforced concrete structural use consists of a residual strength ≥ 50% of first crack strength. The fiber reinforced concrete, depending on the quantity of reinforce-ment it has got, will have the possibility of being more exploited at a structural level and offering a resistant capacity equal or greater than the maximum one reached in service by plain concrete.

CTODCTOD0

LOAD

Pmax

Pmax available for thecalculation of the design Mr,in conventional concrete

Minimum FS=1.7 forplain concret

Plain concret behavior

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6. Appliances in fiber reinforced concrete. Floors design.

In this case the shrinkage control framework is placed in the third superior of the provided section, letting concrete bear the stresses due to acting loads.

Here’s an example with a typical section.The initial conditions are:

- Floors with 15.00 cm of thickness in concrete f´c = 25 MPa, Modulus of cracking of 3.2 MPa. - Minimum steel quantity, for shrinkage and temperature, in welded wire mesh fy = 414 N/mm2, bars with diameter 6.00 mm spaced out of 15 cm in both ways. - Soil modulus of reaction between 0.09 and 0.12 N/mm3. - Maximum loads: goods lifts with capacity of 6 ton.

The aim is to prove that, with the same structural behaviour, fiber reinforced concrete has got for this case mechanical characteristics equal or superior to those that could be obtained with a traditional reinforced concrete.

The resistant moment of the reinforced section is equal to:

where:

Mres

= Resistant moment;

fy = Steel resistant strain;

d = Usable height.

It’s possibile to replace the traditional framework using fiber reinforced concrete with 20 kg/m3 of steel fibers FF1 (MACCAFERRI), considering as bending strength of a fiber reinforced element of a rectangular section:

Figure 6.21 - Basic project of the concrete with reinforcement for temperature. Floor 15 cm of thickness.

ArmorConcrete

soil

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6. Appliances in fiber reinforced concrete. Floors design

CTOD 0

f If

CTOD 0+0.6mm CTOD 0+3 mm CTOD

U2U1

F > 0.5 f for a estructural use.eq if

Fiber reinforced concret behaviour

Graphic 6.4 - Example of level of minimum performance for the structural use of the concrete reinforced with fibers.

Wirand FF3-30 - C40/50

0

1

2

3

4

5

6

7

8

9

0.0 0.1 0.1 0.2 0.2 0.3 0.3

CTODm (mm)

Nom

inal

stre

ssN

( MP

a

(

Graphic 6.5 - Example of a concrete reinforced with fibers with elasto-plastic behavior.

Nowadays in the European environment there are normative proposals which underline these con-cepts:

- DESIGN , PRODUCTION AND CONTROL OF STEEL Fiber REINFORCED STRUCTURAL ELE-MENTS - Standard UNI U73041440

- Rilem TC162-TDF “Test and design methods for steel fiber reinforced concrete”.

These regulations have the aim of determining the mechanical properties of fiber reinforced concrete, that is the first crack strength and the post-crack residual strengths.

The increase of residual strength may vary from 50% up to more than 100%, depending on the quan-tity of fibers used, for measurings which may vary from a minimum of 20 kg/m3 up to 60 kg /m3.

Reinforced floorings and floors for shrinkage and temperature.

An applicatory example of fiber reinforced concrete is that of floors reinforced only for shrinkage and temperature, in which the provided section has been designed according to the criteria stated in ACI 360 R.

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6. Appliances in fiber reinforced concrete. Floors design.

In order to determine fiber reinforced concrete equivalent strength the results rising from bending tests according to Norm UNI11039 have been considered; for strength C25 and for measurings of 20 kg/m3 the first crack strength is of 3.2 MPa and the minimum ductility of 50-55%.

Table 6.10 - Schedule of UNI 11039 tests results.

Resitencia vs. DosificaciónHormigónes C25

0,00

0,50

1,00

1,50

2,00

2,50

3,00

3,50

0 5 10 15 20 25 30 35 40 45

Dosificación en Kg/m3

Resi

sten

cia

enM

Pa

Strenght vs. dosageConcrete C25

Dosage fiber (kg/m )3

Equi

vale

ntst

reng

ht(M

Pa)

Graphic 6.6 - Curves of equivalent strengths vs. steel fibers measuring.

The determination of fiber reinforced concrete equivalent strength can be obtained also according to the regulations ASTM, RILEM, EFNARC, European.

The shown methodology is a sufficient subject to prove the equivalence of the technical solutions.

The solution in fiber reinforced concrete, besides being equivalent to the traditional one, offers ad-ditional advantages at the level of concrete performances as the better fatigue behaviour and the better crack control.

Sample

FF150L25D20A

FF150L25D20B

FF150L25D20C

FF150L25D20D

FF150L25D20E

FF150L25D20F

FF150L25D20G

FF150L25D20H

Midium value

20

20

20

20

20

20

20

20

0,0178

0,0178

0,0178

0,0178

0,0178

0,0178

0,0178

0,0178

0,0178

V(kg/m )

3

CTOD(mm)

0

50

50

50

50

50

50

50

50

L/d

3,208

2,658

2,725

3,505

3,484

3,581

3,114

3,033

3,164

I(MPa)

2,128

1,161

2,023

2,752

1,694

2,545

1,560

2,032

1,987

eq(0-0,6)(MPa)

eq( )0,6-3,0

(MPa)

1,913

0,563

1,667

2,601

1,574

2,382

1,396

2,210

1,788

D0

0,663

0,437

0,742

0,785

0,486

0,711

0,501

0,670

0,624

D1

0,899

0,485

0,824

0,945

0,929

0,936

0,894

1,088

0,875

Test UNI 11039, Concrete C25/30

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6. Appliances in fiber reinforced concrete. Floors design

MECHANICS OF THE NOT LINEAR CRACK AS TOOL OF ANALYSIS OF Fiber REINFORCED CONCRETE.

The measuring of a flooring based upon the elastic behaviour (Westergaard or FEM) doesn’t allow to exploit the mechanical properties of fiber reinforced concrete.

One of the alternatives developed in the latest years consists in implementing the not linear crack mechanics (NLFM).

The crack mechanics applied to the floorings on elastic soil in fiber reinforced concrete has been valued numerically and experimentally, using the “fictitious crack model”, by Hillerborg, Modeer and Petterson (1976), Plizzari - Meda (2004).

The experimental research allows to determine the shape of the strain curve vs. crack opening, which is numerically represented with constitutive laws of various geometry (linear, bilinear, trilinear, ex-ponential or hyperbolical). In case of fiber reinforced concrete it’s used a bilinear law in which the first phase of the curve is dominated by the post-crack behaviour of the material with a high curve gradient (mesh of the aggregates) and, afterwards, when the micro-crack turns into macro-crack, there is the activation of the strength to the fibers unthreading.

Figure 6.23 - Constitutive law. Curve of Strain vs. Stress in phase of pre peak and strain curves vs. crack aperture in the phase of post peak.

The constitutive connection (or law) has been determined through numerical simulations of UNI 11039 tests in which the connection s-w of the material has been varied until the numerical curve has turned out to be in good accordance with experimental results. The following characteristics of the material are considered:

- Traction strength obtained through direct traction tests; - Modulus of Elasticity; - Modulus of Poisson assumed equal to 0.20.

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Figure 6.24 - Mathematical description of a bending beam according to UNI11039, (a) Evident crack model, (b) Spread crack model.

(a)

(b)

It’s obtained a numerical expression which gauges the numerical behaviour with the experimental one obtained in tests, adopting this matrix of behaviour as analysis model of different sections. It’s clear that, as this behaviour depends on the quantity of fibers and quality of concrete, it’s necessary to check the constitutive law whenever one of the variables changes.

Wirand FF1-30 - C30/37 - Vf=0.38%

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.,0

4.5

0.00 0.05 0.10 0.15 0.20 0.25 0.30

CTODm (mm)

Nom

inalstress

N( MPa

FEA Diana SmearedExperimental

(

Graphic 6.7 - Numeric simulation of tests UNI11039 with Software DINA, the fine curves are experimental and the thick curve represents the gauged curve in FE.

The University of Brescia has developed mathematical models and carried out experimental tests for plates resting on the soil, generating matrixes of behaviour for plates for different soil conditions, loads and concrete classes of strength.

• Shiftfromratios-w to ratio s-e dividing w with the square root of the middle area of the analysed element.

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165

Photo 6.13 - Springs installation to simulate a Winkler soil. Photo 6.14 - Experimental settlement.

Photo 6.15 - Steel springs to simulate an elastic foundation. Photo 6.16 - Steel springs to simulate an elastic foundation.

The modelling has allowed to analyse the mechanism of cracking of a plate resting on the soil, marked out by a crack according to the medians, confirming the experimental results.

Figure 6.25 - Comparison of numerical and experimental results for the plate.

(c)

(d)

0

50

100

150

200

250

300

0 0.5 1 1.5 2 2.5 3 3.5 4Displacement [mm]

Load

[kN]

Slab P4 Experimental

Slab P4 NLFM analysis

Crack

Load

(kN)

Slab P4 Experimental

Slab P4 Analisys

Displacement (mm)

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6. Appliances in fiber reinforced concrete. Floors design.

The research program, numerical and experimental, has got as result the generation of abacuses for the thickness premeasuring of the plates in fiber reinforced concrete under punctual concentrated loads, different soil carrying capacity conditions, concrete strength classes, type and measurings of steel fibers.

0

100

200

300

400

500

600

700

800

100 150 200 250 300 350 400

Slab thickness [mm]

Load

Failu

re[k

N]

(1) (2)

(3)0

100

200

300

400

500

600

700

800

100 150 200 250 300 350 400

Slab thickness [mm]

Load

Failu

re[k

N]

(1) (2)

(3)

Ulti

mat

eLo

ad[k

N]

0

100

200

300

400

500

600

700

800

100 150 200 250 300 350 400

Slab thickness [mm]

Load

Failu

re[k

N]

(1) (2)

(3)0

100

200

300

400

500

600

700

800

100 150 200 250 300 350 400

Slab thickness [mm]

Load

Failu

re[k

N]

(1) (2)

(3)

Ulti

mat

eLo

ad[k

N]

Abacuses in functionof the kind of soil.

Slab tickness (mm)

Ulti

mat

elo

ad(k

N)

Graphic 6.8 - Design abacuses for a plate resting on the soil with a volume fraction Vf = 0.38% of fibers 50/1.0 in a concrete matrix C25/30.

The sequence of crack, with the help of a software to the finished elements, working in a not linear environment, allows the modelling of any load condition. What is fundamental, it’s the character-ization of the material for mixture strength class, according to its modulus of crack and the specific measuring, for the determination of the connection s-w and for the characteristic curve of not linear behaviour, which will become the basis for the analysis to the E.F.

6.5 - Fiber reinforced concrete and the joints design.

Fiber reinforced concrete offers the possibility of increasing the spacing between the control joints in comparison with what turns out in the traditional formulations previously discussed.

Everything is based on the capacity of a homogeneously reinforced section of resisting the effects due to temperature and shrinkage in comparison with the traditional solution, which has only got a steel layer placed in the resultant of the stresses triangular diagram. The basic concept is the trans-formation of this strains diagram, from a triangular diagram to a rectangular diagram owing to the material resistant effect in its whole section, as it is shown below:

Figure 6.26 - Diagram of base presented with traditional solution.

ArmorConcrete

soil

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6. Appliances in fiber reinforced concrete. Floors design

Concrete reinforced with fibers

soil

Figure 6.27 - Diagram of stresses owing to temperature in a fiber reinforced plate.

The addition of fibers may lead to an increase of joints spacing from 30% up to 100% out of the one originally provided by the present codes.

The possibility of manifacturing plates with greater dimensions is a reality based upon two funda-mental bonds:

- Plate thickness; - Quantity of reinforcement.

ACI 360R, in the “Sub Grade equation”, previously shown, provides for these parameters and allows to reach spacings wider than 10 metres, up to a maximum of 30 metres.

It turns out evident that the solution will be orientated towards high measurings of fibers, owing to the necessity of reinforcement, and to remarkable thicknesses, in many cases greater than 18 cm, to resist the effects of curling and warping.

Here is the description of a couple of examples of increase of joints spacing, one for a standard floor and one for floors highly reinforced for shrinkage.

Example Nr.1 Attic 15 cm thick, minimum steel and shrinkage.

- Floor thickness 15.00 cm in concrete f´c= 25 MPa; - Minimum quantity for shrinkage and temperature, in welded wire mesh, fy = 414 N/mm2, bars diameter 6.00 mm and with spacing of 15 cm in both ways. Placed in the third superior. - Soil modulus of reaction between 0.09 and 0,12 N/mm3.

Figure 6.28 - Concrete slab with reinforcement for temperature. Floor 15 cm thick.

ArmorConcrete

soil

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Proposed fiber reinforced solution:

Concrete reinforced with fibers

soil

Figure 6.29 - . Slab in fiber reinforced concrete. Floor 15 cm thick.

Calculation of the mechanical equivalence between the two solutions:

N/mm

N/mm

N/mm

%

mm

mm

kg/m

kg/m

mm

mm

mm

mm

Nmm

kg/m

mm

Nmm

2

2

2

2

3

2

3

Measureunit

Mesh Fibers6/150 FF1 (1.00x50)

Comparison Traditional Reinforcement vs. Fibers Thickness = 15 mm

Mesh traction strength

Concrete with fibers bending traction strength (21 Mpa)

Concrete equivalent resistance (per 20 kg/m of fibers)

Ductility of concrete with fibers

Diameter of the mesh

Section of the mesh

Weight of the mesh/m2

Weight of the mesh /m

As = mesh resistant area

b = base of concrete section

h = concrete theoretical thickness

d = section usable thickness

M = Mesh Maximum Bending Moment

H = Proposed section thickness

M = Maximum Bending Moment of Concrete with fibers

3

3

Advised measuring

414,00

6,00

150,00

2,96

19,73

188,50

1.000,00

150,00

80,00

5.618.676

3,20

1,76

55,50

1.000,00

138,40

150,00

20

150

6.600.000

Characteristics

It’s obtained the mechanical equivalence of a fiber reinforced concrete, measured with 20 kg/m3 of Wirand® FF1 fibers, for the section reinforced in a traditional way.

According to PCA advice on spacing between joints, ACI 360R, the plates must be provided with joints with maximum distance of 4.95 m in case of floors without reinforcement for shrinkage and temperature (15 feet).

Table 6.11 - Cálculo da equivalência mecânica entre as duas soluções.

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If the formula “Subgrade drag equation” is applied:

where:A

s = Steel area in square inches per linear foot;

fs = Allowable reinforcement steel strain in psi;F = Factor of friction;L = Provided distance between joints;W = Plate weight in psf, considering 12.5 psf per inch of thickness.

That is:

5 ''67

''''

8 ''9 ''10 ''

101214161820

131518202324

151821242730

Slabthickness ''

Slumpless

than 4''.Aeggregat

< / ''.3 4

Aggregate> / ''.3 4

Slump 4 to 6 inches

Table 6.12 - Reinforcement analysis according to ACI 360-R, Design Slabs on Grade.

Table 6.13 - Spacing calculation of between joints, according to ACI 360-R.

On the basis of what explained, by calculating the maximum spacing in case of traditional reinforce-ment, according to ACI 360 R, and considering the structural equivalence of the provided fiber rein-forced section, the reachable maximum spacing can be of 8.00 x 8.00 m for control joints, obtaining that way an increase of 60% in comparison with the traditional spacing.

Example Nr. 2. Attic 18 cm thick, with strong shrinkage reinforcement.

Distance calculation between joints according to ACI 360RFormula of resistance of the sub-base

(Subgrade Drag Equation)Mesh 6/150

DiameterSpacing2Steel area

fsPlate thickness

wF

Unit of measuremmmm

Inch /pie linaelpsi

Inchpsf

Adimensional

2

Value6,00

150,000,07

30.000,005,9173,82

2Minimum spacing suggested

for contraction joints26,72 pés

8,14 m

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ArmorConcrete

soil

Figure 6.30 - Basic outline of concrete with temperature reinforcement. Thickness pavement 18 cm.

- Floor thickness 18.00 cm in concrete f´c = 25 MPa. - Minimum quantity for shrinkage and temperature, in welded wire mesh, f

y=414 N/mm2,

bars with diameter 12.5 mm, spaced out 150 mm in both ways. - Soil modulus of reaction between 0.09 and 0.12 N/mm3

- Maximum load, unknown.

Proposed fiber reinforced solution:

Concrete reinforced with fibers

soil

Figure 6.31 - Diagram of base presented with fiber reinforced solution. Floor 15 cm thick

Mechanics equivalence mechanics calculation between both the sections:

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6. Appliances in fiber reinforced concrete. Floors design

It’s obtained the mechanical equivalence for a fiber reinforced concrete, measured with 40 Kg/m3 of Wirand® FF1 fibers, for the traditionally reinforced section.

Reinforcement analysis according to ACI 360 R-Design Slabs on Grade.

N/mm

N/mm

N/mm

%

mm

mm

kg/m

kg/m

mm

mm

mm

mm

Nmm

kg/m

mm

Nmm

2

2

2

2

3

2

3

Measureunit

Mesh Fibers

Comparison Traditional Reinforcement vs. Fibers Thickness = 15 mm

Mesh traction strength

Concrete with fibers bending traction strength (21 Mpa)

Concrete equivalent resistance (per 40 kg/m of fibers)

Ductility of concrete with fibers

Diameter of the mesh

Section of the mesh

Weight of the mesh/m2

Weight of the mesh /m

As = mesh resistant area

b = base of concrete section

h = concrete theoretical thickness

d = section usable thickness

M = Mesh Maximum Bending Moment

H = Proposed section thickness

M = Maximum Bending Moment of Concrete with fibers

3

3

Advised measuring

Characteristics12,7/150 FF1 (1.00x50)

414,00

12,40

150,00

12,64

70,22

805,09

1.000,00

180,00

70,00

20.998.239

4,00

3,92

98,00

1.000,00

179,28

180,00

40

180

21.168.000

Table 6.14 - Comparison of a rectangular section with traditionally bending reinforcement vs. steel fibers reinforced section.

Table 6.15 - Distance between joints calculation , according ACI 360 R.

Distance calculation between joints according to ACI 360RFormula of resistance of the sub-base

(Subgrade Drag Equation)Mesh 12.70/150

DiameterSpacing2Steel area

fsPlate thickness

wF

Unit of measuremmmm

Inch /pie linaelpsiInchpsf

Adimensional

2

Value12,70150,000,29

30.000,007,0988,582

Minimum spacing suggestedfor contraction joints

99,7530,40

pésm

A control joints spacing of 30 m is obtained.

As the quantity of incorporated fibers offers the same resistant capacity of the analysed rectangular section, it can be inferred that joints spacing might keep this level. It’s necessary to be careful as, for

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6. Appliances in fiber reinforced concrete. Floors design.

6.6 - Control of quality in fiber reinforced concrete for floorings.

The control of quality of fiber reinforced concrete for floorings must be carried out according to the same criteria recommended for materials, so as to verify the mechanical strengths considered in the design. The design responsible engineer will have to guide the carrying out of these tests, in order to determine the material bending strength, compression and residual strength.

Besides the control of the material mechanical properties, there are basic recommendations to follow in the correct design of the mixture to use in floors:

- Limitation of water/cement ratio, recovering the workability through the use of fluidifying additives; - The use of prevailing inerti greater than ¾ “ succeeds in reducing the effect of shrinkage in the mixture, as to incorporate inerti of greater dimension affects the water demand;

- It’s advisable to use cements Type II, in comparison with Type I and Type III, as these, nor-mally, increase the use of water in the mixture;

- To use slumps or lowering cones at a level between 4” and 6”, in function of the kind of laying (mechanized or manual);

- As for the solutions of increased distance joints it’s advisable to carry out an increase of the resistant section at the plate ends which substantially may help to resist the curling effects;

- It’s fundamental to control the material seasoning process to assure the homogeneity of the hardened material.

the attic minimum thickness of 18 cm, there could arise some phenomena of curling, which could be avoided only by decreasing the spacing, or with the use of building edge joints such as “Omega”, or “Diamond Dowels”, in the plate outline. It’s important to underline that, in order to manifacture floors with widely spaced out joints, it’s necessary to consider some important factors such as an excellent quality of foundation such as the one recommended, minimum value 0.12 N/mm3 of verti-cal modulus of reaction, equivalent to a CBR of 40/45%, great care in concrete seasoning, perfect mixture workability and its continuity during the whole process of the floor laying.

All these conditions make possible this kind of solution, which can’t be put down just to the fact of adding fibers in concrete. Any lack of control in the work concerning the mixture, workability, seasoning, etc may generate problems in the aim of obtaining very spaced out joints without crack troubles.

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6.7 - Current standard situation.

Besides the regulations mentioned in the previous chapters concerning the control of quality of fiber reinforced concrete, here are the following codes of floors design:

- ACI 360R – Design of Slab-on-ground;

- TR-34 – Third Edition – Concrete Industrial Ground Floors;

- UNI 11146 – Concrete floors for industrial use;

- NF P11-213 – Dallages – Conception, calcul et execution; - TR-34 – Concrete Industrial Ground Floors;

- UNI 11146 – Pavimenti industriali;

- NF P11-213 – French code.

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7. Applications of fiber reinforced concrete: prefabricated elements.

7.1 - The use of fiber reinforcement in prefabricated/pre-cast concrete.

The reinforcement of concrete with steel fibers is a common practice as it succeeds in reducing the phenomenon of cracking, improves the durability of the concrete, and in some cases can replace completely the standard steel reinforcing bars.

The pre-cast concrete industry has shown a particular interest in the application of SFRC. Reinforcing with fibers allows to industrialize the process and to improve the material properties of the concrete. In some cases, while it may not be possible to completely replace the traditional reinforcement, there may be the potential to reduce the thickness of the element and review the minimum cover thick-ness required.

The use of fiber reinforcement in structural elements is becoming more common, especially in the pre-cast concrete industry, where exhaustive quality control testing is required by national codes. A high degree of quality control during the production process allows the designer to rely upon the mechanical properties of the material. In the case of fiber reinforced concrete, it is important to ensure a good distribution of fibers in the matrix in order to achieve the desired material properties.

One of the most recent and meaningful applications in which fibers are used as structural reinforce-ment is in underground works. It is used in conjunction with some methods of tunnel excavation through which prefabricated elements are used as final covering where fibers replace, at least partially, the traditional reinforcement.

Some examples of prefabricated elements where the steel fibers reinforcement has been successfully used are:

a) Non-structural elements where the main function of the steel reinforcement is the supply of ductility and the limitation of crack phenomenon.

b) Pre-cast concrete pressure pipes, when there is no danger of life for people.c) Sleepers on which trains rails are resting, in which the main problem consists in fatigue

phenomena due to cyclical loads. It has to be specified that fibers have a function comple-mentary to the main reinforcement.

d) Pre-cast structural panels used in the construction of industrial building.

Apart from the possible applications previously mentioned, there are many other cases where steel reinforcement can be beneficial. Structures designed for different types of impact loading may be another possible application.

Although there are many applications in which fibers are used, in practice, the potential advantages they can offer must still be exploited. This is due to the lack of regulations for the use of fibers as concrete reinforcement. In fact, the existing regulations would fit with difficulty to Fiber Reinforced Concrete (FRC) as, to design with this kind of material, it is necessary to consider the material plastic phase, as fibers start working after concrete crack initiation, while with the traditional steel bar rein-forcement, the material behaves in a linear manner. (Fig. 7.1)

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figure 7.1 - Bending test. Typical response of beams reinforced with steel fibers (a) and with traditional steel (b).

7.1.1 - Final remarks.

There is increasing interest in the use of fiber reinforced technology in pre-cast/prefabricated concrete structures. It has been recognized that steel fibers can be used to replace traditional steel (totally or partially), improve concrete performance, and reduce production costs and production cycle times. There are many advantages to incorporating fibers into the concrete mixture, primarily due to the reliable mobilization and utilization of residual strains.

At this time, no formal design codes have been developed specifically for steel fiber reinforced concrete, making it difficult to promote the use of this technology. Design recommendations and guidelines (RILEM - TC162-TDF) have been prepared by some national agencies and industry associations, but there has been no formal acknowledgement of this material into building codes. Clear and simple rules are required by designers who are prepared to take the responsibility of working with this material.

A recent example of a step in this direction is the latest recommendation of the organization charged with drawing up the Italian standard UNI U73041440, Design, Carrying out and Control of Structural Elements Reinforced with Steel Fibers. This standard covers the main criteria to allow for the insertion of steel fibers in order to replace, totally or partially, traditional steel in structural elements.

7.2 - Design of precast segment in fiber reinforced concrete.

One of the possible and, at the same time, most promising structural applications of fiber reinforced concrete, is certainly the one which refers to the manufacturing of rings for prefabricated panels (ring segments) for the use as tunnel liners in projects excavated with the use of Tunnel Boring Machines (TBM).

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7. Applications of fiber reinforced concrete: prefabricated elements.

The use of metal fibers as a partial or total substitute of traditional steel reinforcement in this ap-plication is especially advantageous when:

- The typical conditions of saturated cohesionless soils make difficult the predictions of the stresses which operate in the tunnel cross and axial sections and, consequently, many of the hypoth-eses put forward in the design of the covering of tunnels built with integral excavation machines (TBM) must be accepted although they have an important negative impact on the carrying out or on the economical aspects. Under this point of view, to be able to rely on the stiffness characteristics of a material as concrete reinforced with steel fibers, is of fundamental importance as the combination of bending moments and of the normal forces applied in tangential direction is particularly favourable for the use of this material as substitute (at least partial) of the traditional reinforcement; - SFRC offers a good ductility in relation with the splitting crack and good impact resis-tance; - SFRC allows in general a better control of the possible local collapses of the covering por-tions.

Schnütgen (2003) has investigated different kinds of load for the ring segments of the subway system in Essen, Germany (Fig. 7.2) and has experimentally verified the positive contribution of steel fibers in relation with splitting crack as, after the crack has come about, the applied load has kept increasing until it has doubled the first crack one. The same author has verified the behaviour of key ring segments and has proposed some design formulae based upon the RILEM TC 162-TDF (2000, 2002) work.

Further studies have been produced by Mashimo and others (2002) Kooiman and Walraven (1999).

Figure 7.2 - Conditions of analysed loads (Schnütgen, 2003).

Bending test (transportation state)

Shear test

Plastic deformable supporting pads

Hidraulic jacs

Plastic deformable supporting pads

Hidraulic jacs

Test of in plane actions (placing situation)

Splitting test

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7. Applications of fiber reinforced concrete: prefabricated elements.

The study of prefabricated ring segments in SFRC can be completed through numerical analyses with programme to the finished elements in which the main load conditions to which they will be subjected are studied. This section will present a methodology that can be used for this numerical study.

In order to carry out a study with a programme to the finished elements, it is necessary to define in advance the framework detailed structure, the specific loads and the bonds, so as the equivalent traction strength for fiber reinforced concrete bending besides its curve of behaviour.

As example, and to understand better the methodology to follow, here are described the analyses achieved with the programme Abaqus 6.4.1 (2003) for one of the segments used in the liner rings of the Barcelona underground.

Fig. 7.3 shows the geometrical characteristics of a typical ring segment for the Barcelona project. Fig 7.4 shows the typical loading conditions corresponding to the critical phase of thrust (TBM thrust); the TBM must be able to push off against the last completed segment ring in order to move forward.

Figure 7.3 - Cross section and plan view of a ring segment.

Frontal view Support platesScale

Scale

Support plates e = 2mm

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figure 7.4 - Load scheme during TBM thrust .

Analyzed segmentedring panel A1

Jackingthrust

Direction ofthe excavation Soil thrust

Jackingapplication region

Fixed consideredring lengthwise

Lateral friccion

TBM shieldAnalyzed segmented ring A1

Fig. 7.5 shows a typical situation of voids in the annular space around the ring segments. This situation will subject the ring segments to bending loads. This situation has been experimentally modelled at the Universidad Politécnica de Cataluña (UPC) with laboratory bending tests (Gettu et al., 2003; Photo 7.1).

Figure 7.5 - Bending on the segment due to the insufficient filling of the annular space (overdigging)between the covering ring and the digging perimeter (Gettu et al., 2004).

Injectedfilling

Soil/rock

Tunnel

Segmentsring

Inadequatefilling

Photo 7.1 - Configuration of plain bending test (Gettu et al., 2004).

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7. Applications of fiber reinforced concrete: prefabricated elements.

Graphic 7.1 shows the experimental results (upper and lower limits) concerning the load as a function of the displacement of the fiber reinforced ring segment and of the fiber reinforced ring segment with traditional reinforcement (mixed reinforcement). A slightly declining behaviour of the segment with just the fibers was observed. Hardening behaviour of the ashlar with mixed reinforcement was also observed.

In order to verify the ABAQUS 6.4.1 (2003) model, the experimental results have been afterwards simulated with analyses to the finished elements, based on the crack mechanics, achieved with such programme; obtaining a good approximation (Graphic 7.1), there has been a confirmation of the used numerical model.

Graphic 7.1 - Comparison between the experimental and numerical Load-Arrow curves.

Further numerical analyses have been carried out with the aim of considering the stresses that are produced when there are especially meaningful situations of load that affect transitory phases, during ashlars manipulation and during ring assembling.

In particular the critical phases analysed with simulation to the finished elements, have been the two following:

1) Thrust on the arch central ashlar during TBM advancing;2) Load on the ring segment that supports 6 other segments during storage.

In the thrust phase, the TBM hydraulic jacks apply loads on specific areas of the cross section of the previously assembled ring, that are large enough to cause the concrete to crack, as the ring itself is the “contrast” necessary to allow the extension of hydraulic jacks that provide the thrust to propel the TBM forward during the excavation.

In the particular case of the Barcelona Underground, there are 4 hydraulic jacks for each ring seg-ment and 2 for the key segment, for a total of 30 (7 x 4 + 2) jacks operating on the ring. The thrust from each jack varies as a function of the soil characteristics and of the tunnel depth, reaching 3 MN when the tunnel axis is placed at a depth of about 25 m.

Load

(kN

)

Deflection (mm)

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7. Applications of fiber reinforced concrete: prefabricated elements.

For the central segment of the inverted arch, the numerical model has been worked out with a mesh of 3D elements of medium dimension equal to about 90 mm. The following situations have been considered in the analyses (shown in Fig. 7.6):

Figura 7.6 - Schemes of loads and bonds of the ring segment subjected to the jacking thrust.

- The last completed ring receives the jacking stresses prior to completion of the filling of the annular space between the ring and the soil (grouting), while at the same time, the filling of the space between the immediately front ring and the soil has yet to solidify. The void corresponding to the front ring has already been filled and the filling has set, therefore it can be considered as a rigid support in the direction of the tunnel axis;

- The ring support is considered uniform as along there are polyethylene panels (pad) at the contact locations between the rings. It is considered elastically capable of being deformed as it’s necessary to contemplate the front ring axial changeability which in addition represents an unilateral bond which doesn’t resist to traction;

- The unilateral rigidity of the springs which simulate the changeability of the ring support, that is the front rings changeability, has been suitably gauged through imposed displacements analyses;

- The interaction of the segment with the adjacent segments of the same ring is, too, always unilateral, as the ring segments are simply in contact and assembled with pins;

- The lateral friction which can be generated between such lateral surfaces of the adjacent ring segments is not considered and there are positioned springs which operate in compression normally to surfaces. Also the rigidity of these springs has been suitably gauged to simulate the changeability of the adjacent ashlars;

- The four jacks operate on the segment through metallic plates which can be considered rigid, distributing the load uniformly on the respective contact areas.

Fig. 7.7 show the typical numerical results obtained by the simulation of the behaviour of a ring segment with 45 kg/m3 of Wirand FF1fibers.

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7. Applications of fiber reinforced concrete: prefabricated elements.

From Graphic 7.2, both the presence of splitting cracks corresponding to the service load, and the load increase (after the crack) made possible by fibers can be observed.

Fig. 7.7 shows the distribution of the radial strains in the four load zones (the four jacking plates) corresponding to the service loads.

Graphic 7.3 show the distribution of radial stresses (sr) during the depth of the ring segment in

direction (z) of the tunnel axis, as a function of the service load.

It may be observed, under the load zone, a behaviour of the ring segment similar to that of a plate subjected to concentrated loads of great intensity: as a matter of fact, after a tract of about 100 mm, in which there are strains of compression, there show tractions along about 300-400 mm and these tend to disappear to come back again later on the opposite side of the ashlar.

The fact that the traction radial stresses show also in the bottom of the ashlar is simply due to the presence in that zone of the longitudinal springs (which simulate the axial changeability of the ring already built on which the ring object of the analysis is resting) which, being uniformly distributed on the whole rear cross section of the ashlar, generate compression longitudinal strains much more limited and modest local radial tractions.

Graphic 7.2 - Load applied in function of the horizontal displacement.

Figure 7.7 - Radial strains sr in correspondence of the exercise load.

Splitting behavior:First Crack

Service Load

Second crack

Second crack

Load

(kN

)

Maximum load

Deflection (mm)

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7. Applications of fiber reinforced concrete: prefabricated elements.

Graphic 7.3 - Radial strains sr along the ring segment axis.

In order to analyse the solicitationswhich are caused by ring segments during the storage, it is necessary to consider that, generally after the extraction of the form, the ring segments are placed in groups of three after the first day and on the seventh day the stacks are completed with the remaining segments of the ring (in total 7 + 1 key), always using wooden blocking as shown in Fig. 7.8.

Figure 7.8 - Arrangement of the stacked wedges with the critical segment highlighted.

The ring segment at the base of the stack is positioned on wooden support blocking consisting of two wide surfaces of about 300 mm each, formed by great wooden supports that follow the curvature of the segment placed with a wheelbase of about 2,80 m connected below by struts in order to hold the blocking in position. The next segments are placed on small wooden beams, with an approximate section of 100 mm x 100 mm and length equal to the one of the segments, that will have to be positioned with a wheelbase of 2,80 m so as to remain lined up with the inferior supports in order to remove or at least minimize the bending effects on the segments. In practice, the blocking is typically out of location, resulting in loading eccentricities that may induce strong bending strains in the segment.

In order to analyse in suitable way this phase of load, there have been considered especially unfavourable arrangements of the segments small beams of support and one of these is the one represented in Fig. 7.8, referred to the second segment (Gettu et al., 2004) which rests on some small beams placed with a wheelbase of 2,80 m + 2e

e (meaning with e

e the external eccentricity),

Distance (mm)

Service load

MP

a

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7. Applications of fiber reinforced concrete: prefabricated elements.

For the modelling with the programme to the finites elements Abaqus 6.4.1, the minimum 3D elements of the thrust phase have been adopted, but with a medium dimension near to 90 mm. The load zones correspond to those of the small beams support surfaces (about 100 x 1800 mm) and on such surfaces there has been applied a uniform pressure in vertical direction with the aim of simulating the weight of superior ashlars (Fig. 7.10). The lateral supports are modelled as rigid supports operating in the vertical direction, arranged along the whole depth of the segment.

Figure 7.9 - Geometrical configurations of supports and loads.

while the superior segment is arranged with small beams at a distance of 2,80 m – 2ei (meaning

with ei the internal eccentricity). In this situation the weight of the segments, above the critical load,

operates at a distance from the supports equal to ee + e

i. Once the stack is completed, the second

segment will turn out loaded for the total weight of 5 segments + 1 key. 438 kN correspond to the weight of 6 whole ashlars. The numerical analyses have been developed by adopting for the eccentricity the values (Gettu et aL., 2004), quoted in the same Fig. 7.9.

Figure 7.10 - Mesh bonds and loads for the analysis of the maximum weight of stacking.

The aim of the analyses carried out has been that of calculating how many ashlars can be stacked without causing crack or collapse phenomena of the most stressed ashlars, as the crack control is an aspect of basic importance for the covering ashlars of tunnels for which it’s necessary to assure a perfect watertight seal being therefore essential to avoid the production of cracks also in the transitory phases as for instance the storage one.

The numerical elaborations have been achieved under the hypothesis of presence of eccentricity and letting progressively grow the load operating on the ashlar up to the forming of the first crack. The

ei = ee = 250 mm ei = ee = 500 mm

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7. Applications of fiber reinforced concrete: prefabricated elements.

crack is discovered for the presence of plastic distortions, as code Abaqus is based on a spread crack model.

In the condition of simulated load, after the crack forming there takes place also the collapse of the segment being the framework of isostatic kind and the material is represented as homogeneous along the depth of the segment (the crack forms immediately along the whole depth of the segment), which prevents the redistribution of the internal actions.

The analyses have been carried out referring to the concrete mechanical characteristics after two different periods of hardening, equal to 4 days and 28 days respectively. The first condition has the aim of verifying the behaviour in conditions very similar to the real ones and, as the fresh concrete characteristics after 4 days can’t be directly determined, these are calculated on the basis of those corresponding to concrete after 28 of hardening, using for this purpose the correlative expressions provided by the Eurocodes. The second condition has the aim of obtaining numerical results by using the characteristics of the material experimentally determined.

Graphic 7.4 - Applied-Arrow load in the second ashlar with eccentricity of 250 mm.

Load)

NumericalNumerical

Tunnel segments: non linear analyses,stacking teste,

Service load

Load

SFRC (28 days)SFRC (4 days):

In Fig. 7.4 there are represented diagrams in terms of applied load and of arrow valued in the half of the second ashlar with e

e = e

i = 250 mm. It may be observed that, already with 4 days of hardening,

the second ashlar is in condition of supporting the exercise load of 6 superior ashlars. After 28 days of hardening, the segment shows naturally a rigidity and a last load superior and is in condition of supporting the weight of almost 10 ashlars stacked one on another.

In the end, the segment achieved with Wirand FF1 fibers, with measuring of 45 kg/m3, allows, in presence of not excessive eccentricities and anyway within a limit of 250 mm, to stack the 6 ashlars necessary for the forming of a ring.

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7. Applications of fiber reinforced concrete: prefabricated elements.

CONCLUSIONS

From the numerical analysis carried out for the ring segments of the Barcelona Underground, it is possible to conclude that for these types of structures, it is possible to partially replace the traditional steel bar reinforcement with steel fibers.

Given the high stresses which can be reached in the thrusting phase of the jacking operation around the perimeter of the precast segments (the first 400 mm), and the guarantee that in the intermediate part of the precast segment the reinforcement with fibers is in conditions of facing the strains which can be reached, it can be concluded that the segment need only be reinforced with traditional bars at the perimeter of the segment.

Figure 7.11 - Traditional reinforcement + Fibers (a). Traditional reinforcement (b).

7.3 - Examples of applications. Padding panels, prestressed beams, non-structural prefabricated elements.

7.3.1 - Closing panels.

Testing on prefabricated concrete panels reinforced with both with traditional reinforcing steel and with steel fibers has been carried out.

This testing was done in order to provide a framework to conduct research into the methods to optimize the structure of the panel considering the static stresses, the production process and the reduction of weight.

The main focus of the research has been the replacement of the traditional steel welded wire mesh, typically positioned near the external front face of the panel, with steel fibers.

The primary goal of the research was the development a load model that would represent the loads that the wind could generate on the panel. The panels vertically placed are subjected to cross loads owing to the effect of the wind and to a limited axial load, caused by their own weight. It is neces-sary to combine the bending strains due to the self weight of the panel with those derived from the wind loads. (Fig. 7.12 and Photo 7.2).

RCOTRF TR

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7. Applications of fiber reinforced concrete: prefabricated elements.

Concret

Polystyrene

ConcretFinishing gravel

20 105

23

The tests have been carried out on full scale panels (dimensions of 11.2 m by 2.5 m (L x H)). The results of these tests show that in the panel reinforced with steel fibers it’s obtained a ultimed load similar to the panel reinforced with welded wire mesh and moreover it’s possible to control in a more effective way the generated cracks.

Photo 7.3 - Test on horizontally placed panels.

7.3.2 - Double T covering prestressed beams. The steel fibers can be used in double T prestressed elements. In such frameworks there are no problems and need only be reinforced with longitudinal steel. The double T section elements are com-monly reinforced on the flanges with a steel mesh in order to obtain better behaviour to concentrated loads, shear and torsion strength, especially at the last limit state where it’s considered that torsions represent the most critical stresses.

The research carried out to date proves that if the cross steel (Φ 5/25) is replaced by moulded steel fibers on the ends (50 kg/m3), and the rest of steel is not modified (Fig. 7.13), then there are no modifications in the bending longitudinal behaviour of the elements (Fig. 7.14).

Photo 7.2 - Horizontally placed panels. Figure 7.12 - Cross Section of the Traditional Panel.

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figura 7.13 - Double T prestressed beam simply leaned and subjected to distributed load. Load-Displacement Curve in an element reinforced with traditional steel (a), distribution of cracks in the element reinforced with traditional steel (b) and with steel fibers (c).

Figura 7.14 - Double T section element. Cross section (a), traditional reinforcement (b) and reinforcement with fibers (c) on supports.

Deflection (mm)

Load

(kN

)

FRC

(a)(c)

(b)

Head web-reinforcementstirrups

Current web-reinforcementstirrups

Prestressingstrands

Prestressingstrands

Detail of the webreinforcement

Head web-reinforcementstirrups

Strands

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figura 7.15 - Cutting test. Load model (a); Load-Cutting Behaviour (b); crack mode with not reinforced concrete (c); with traditional steel (d) and with steel fibers (e).

Besides studying which would be the distributed loads to which the framework will be subjected, it has been studied the way of simulating them in laboratory. Some tests have also been carried out on the element without any kind of framework (in the matrix there have been inserted no fibers or welded wire mesh).

The comparison shows the interaction of various kinds of loads, besides those which generally are considered (punctual loads, cross bending strains, distributed loads).

In this way the ductile behaviour to the framework cutting has been assured when the framework corners have given way.

Due to the dynamic parameters selected , on the other hand, expressed by the results that refer toed the vertical displacements, they were obtained fragile results, except for the concrete element without armor that was broken before, due to inflection.

7.3.3 - Structures for flat coverings.

This kind of framework marks itself out for its great slenderness (ratio depth/longitude up to 35), a thin section in the compression zone to allow the drainage of water and the stresses laterally distributed, which generates meaningful cross bending moments. Once studied the critical loads to which the framework will have to be subjected during its usable life, the corresponding tests have been carried out in the University of Brescia (Italy) laboratories. The test has been carried out with four loads points, which are described in Fig. 7.18a. An electromechanical sensor has been positioned in the half of the framework supported with ring nuts with two metal bars welded to a metal beam.

(e)

(d)

(c)

(b)

(a)

Deflection (mm)

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7. Applications of fiber reinforced concrete: prefabricated elements.

The tests have been carried out on three different models with the same structure: the former two models have been reinforced with steel fibers, one with low carbon contents fibers with 30 mm of length and 0.7 mm of diameter, the other with high carbon contents fibers with 30 mm of length and 0.4 mm of diameter, while the third one has been reinforced in traditional way with welded wire mesh (1Φ5/25/20).

The elements reinforced with steel fibers have shown a greater ductility and a greater service last load in comparison with the model reinforced with traditional steel (Fig. 7.18a). The breaking, in any case, has been caused by longitudinal bending moments with cracks on the framework flanges (Fig. 7.18b, c, d).

It can be inferred, after the tests carried out, that steel fibers represent a reinforcement homogeneously distributed in the matrix which can compete with the traditional steel mesh, and moreover allow to reinforce in effective way frameworks of complex sections which have stresses both in two and in three directions.

The behaviour of the frameworks of prefabricated flat coverings in concrete reinforced with metal fibers is comparable with the one of frameworks reinforced with welded wire mesh and, as the results obtained show, with an increase of ductility.

Figura 7.16 - Cross section (a), displacement of the structural element (b).

Figure 7.17 - Bending behaviour of the structural element (a); Load-displacement curve of the element under distributed loads (b): Horizontal attic (c); flange inclination (d).

Strands

(b)(a)

(a)

(b)

(c)(d) Displacement (mm)

Load

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figure 7.18 - Test in real scale: system of loads (a); simulation of loads (b); measurement equipment (c); behaviour of cracks in the element (d).

Figure 7.19 - Test of the framework reinforced with steel fibers. Symmetrical (a) and asymmetrical (b) section.

(a)

(c)

(d)(b)

(a) (b)

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figura 7.20 - Global behaviour in real scale of the structural element. Last load Vs Deflection (a); Crisis of the structural element reinforced with traditional steel and with steel fibers (b, c, d).

7.3.4 - Pre-casted stretched beams

The possibility of replacing the minimum cross reinforcement (hangers) with steel fibers in prefabri-cated beams may lead to important improvements in the framework performances.

The shear behaviour of prefabricated elements with the minimum cross reinforcement has been studied with tests on full scale beams. The tests simulate the behaviour of the beams close to the supports, where hangers are normally designed according to the building regulations in those places where only a minimum steel is required. The tests have been carried out on beams with no kind of traditional reinforcement (beam 1), with traditional cross reinforcement (Beam 2) and beams rein-forced with steel fibers (beams 3 and 4).

The experimental results prove that the shear behaviour of beams reinforced with steel fibers (Vf =

0.64%) is similar, or better, to those reinforced with the minimum traditional cross steel required by Eurocode 2. Fig. 7.21b shows the cutting-displacement curve of the tests carried out on beams with minimum reinforcement. In any case the crack has started to show (final of the elastic part) when reached a stress to cutting of 450 kN. The behaviour of the concrete beams reinforced both with traditional steel and with steel fibers has produced similar results. It has been possible to notice that, in beams reinforced with steel fibers, the cracks thicknesses have been thinner than those of the beam reinforced with traditional steel.

(a)

(b) (c) (d)

Comparison - Section CLoad - Total displacement

Total displacement (mm)

Elastic limit

First cracksLoad

(kN

)

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7. Applications of fiber reinforced concrete: prefabricated elements.

193

Figura 7.21 - Cutting test. Test in laboratory (a); load-displacement curve in beams reinforced with minimum cross steel (b).

7.3.5 - Different elements.

There are numerous cases in which fibers can effectively replace the traditional reinforcing steel, improving the quality of the element and allowing a degree of optimization to the production process. The cases in which the traditional reinforcement can be replaced with metal fibers are those in which mechanical stresses are limited and when the reinforcement steel will have secondary functions such: crack control, increase of strength to abrasion and impact, improvement of strength to thermal variations.

Examples where the traditional reinforcement has been replaced with metal fibers, can be observed in the following images.

Displacement (mm)

Shea

r(kN

)

Ultimate shear

Ultimate shear

Ultimate design shear

Sericeability shear

Beam 1

Beam 2

Beam 3

Beam 4

(a) (b)

(c) (d)

Model

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figura 7.22 - Example of different prefabricated elements reinforced with steel fibers.

7.4 - SFRC special applications.

7.4.1 - Foundation systems.

Generality

Unlike industrial floor slabs, which are plates resting on elastic soil, foundations are load bearing structures. Their design and construction must be in accordance with the local design and building codes. Fiber reinforced concrete (SFRC) is not regulated in many countries and, consequently, special permission may be required for use in many applications. In Germany, for the application of steel fibers in buildings in which the structural stability must be proved, official permission from the German Institute of the Technics of Civil Building (DIBT) of Berlin must be obtained. Such permission may not be required in relation to floorings and buildings where steel fibers are used only for the analysis of the exercise limit state (SLS). These applications may be of secondary importance as there is no risk for life in case of damages or collapse.

Concrete foundation slabs

In the last 5 years, a new application in building construction has been developed. The concrete foundation slabs for residential buildings may be constructed using SFRC. The weight of the walls can be easily supported by the concrete slabs in SFRC, provided the structure is built on competent soil. The principles of design are the same as industrial floors.

Photo 7.4 - Foundation Slabs SFRC for residential building foundations (private houses), Germany.

(e) (f)

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7. Applications of fiber reinforced concrete: prefabricated elements.

Nevertheless, it is possible to introduce project for the general approval of such systems. In Germany, for example, the general approval can be asked to the German Institute of Technique of the Construction (DIBT) in Berlim.

Photo 7.5 - Concrete foundation slab (diameter: 39 m) for an agricultural silo with combined reinforcement (mesh reinforcement + steel fibers + PP fibers), Germany, 2005.

Foundations for mesh framework of aerial electrical lines

Using SFRC, the foundations for aerial utility services (trams, railway lines, etc.) can be redesigned in order to remove much of the conventional steel reinforcement. The main function of these foundations is to ensure their stability through their own weight (dead weight). The steel fibers work as minimum framework for crack control. Consequently a structural analysis at SLS must be carried out. This control has been achieved through a strut-and-tie system. Conventional reinforcement remains in the upper part of the foundation, typically for anchor bolts and flanges. As these foundations are generally quite large they are typically cast on site.

Figure 7.23 - Cross section of foundations in SFRC for aerial electricity posts (left) and strut-and-tie model for the analysis of internal stability (right).

Base of elements

with conventional reinforcement.

Anchorage length

Fundation.

Vertical armor.

Self weight.

Horizontal armor.

.

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7. Applications of fiber reinforced concrete: prefabricated elements.

The advantage of steel fibers over conventional reinforcement is the decreased installation time and the ease of installation of ancillary services (cable ducts, etc.).

7.4.2 - New potential applications.

Drilled concrete caissons

Steel fibers can improve the construction of drilled concrete caissons. In this application, the steel fibers may be able to replace the minimum reinforcement steel, usually consisting of a prefabricated steel reinforcement cage. These cages are inserted into the fresh concrete, a process that can be cumbersome and time consuming. Fresh concrete with steel fiber reinforcement would substantially reduce the process of setting up, while time of building would be remarkably reduced.

Currently, there are no standards allowing the replacement of a conventional reinforcement in such applications, as that concerns the support of frameworks in elevation.

Photo 7.6 - Field with concrete posts drilled and set up. Photo 7.7 - Drilling plant.

7.4.2.1 - Structures exposed to earthquakes.

Some of the strongest earthquakes in the latest years have proved that new materials and building techniques are needed. The collapse of many structures, together with the death of many people, proves that the kinds of buildings used can’t support the impact of the high dynamic strength which takes place in the strongest earthquakes, due to insufficient capacity of absorption.

Starting in the 1970’s, research has been conducted into the beneficial effect of steel fibers on the behaviour of concrete and reinforced concrete structures subjected to dynamic load. The main interests at that time were the potential safety and the resistance of the nuclear plants and of the military structures of protection:

- Steel fibers improve in meaningful way the deforming behaviour and the ductility.

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7. Applications of fiber reinforced concrete: prefabricated elements.

- The concrete softening capacity of concrete can be improved in meaningful way with the development of new building materials.

- The attenuation of reinforced concrete frequency can be increased up to 10 times with the addition of steel fibers.

- The capacity of dissipation under impact and the stationary cyclical load can be clearly in-creased.

- The strength to impact can be increased up to 2000% with steel fibers.

These beneficial effects of steel fibers on softening and deterioration can improve in meaningful way the stability of the framework subjected to dynamic loads during earthquakes.

A research to measure the ductility in Column-Beam union has proved that the ACI method of calcu-lation together with SFRC, can increase ductility and the union (column-beam) performance, which gives the opportunity of revaluing the global ductility of the framework.

Foto 7.8 - Of steel fiber reinforced concrete in beam-column unions. Thesis presented at the Faculty of the San Diego State University, by Michael Gebman. Year 2002.

7.4.3 - Flooring covering with metal shaped sheets or precast – metal deck.

The fiber reinforced concrete application can be technically justified in case of covering, both the metallic one to cover the collaborating formwork, and that of prefabricated attics systems. In both cases the welded wire mesh is commonly used.

Here follows the technical argument which exemplifies that the fiber reinforced solution at the minimum succeeds in equalling and improving the alternative mechanical conditions, which is provided to be reinforced just to check effects of thermal shrinkage.

Joint # 6Conventional

Joint # 1SRFC 6-in (15.2 cm)

spacing

Joint # 4SFRC 8-in (20.3 cm)

spacing

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7. Applications of fiber reinforced concrete: prefabricated elements.

Figure 7.24 - Traditional section of reinforcement for Steel Deck.

Table 7.1 - Recommendation of reinforcement for Steel Deck shrinkage (Source www.alcor.com.ar).

Both direction Concrete C21

Figure 7.25 - Steel Deck perspective.

Concrete thicknessover the crest

Specification ofthe mesh

Ast. of the specifiedsection (cm /m)2

Minimum ast.(cm /m)2

5-6 cm

8-10 cm

12 cm

15 x 15 - Ø4,2

15 x 15 - Ø6

15 x 15 - Ø6

0.92

1.88

1.88

0.91

1.52

1.82

These are the initial conditions presented in the original design:

- Usable floor medium thickness 8 cm (5 cm of covering on the Steel Deck crest), in concrete fck = 21 MPa.

- Reinforcement steel in rods of 5.00 mm of diameter, fy = 414 MPa, spaced every 15 cm in both directions, located 4.0 cm below the floor surface, according to the recommendations of the manufacturers (source www.alcor.com.ar) or similar.

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Initially the resistant maximum characteristic in the simply reinforced traditional section is obtained with the following:

Where:

Mres

= Resistant moment.

fy = Steel resistant strain.

d = Usable height.

By using the bending strength conventional equivalence of the section traditionally considered by the regulations which include the use of fiber reinforced concrete, it’s obtained the total replacement of the reinforcement provided for 20 kg/m3 of FF1 steel fibers, in which it’s considered as fiber reinforced element bending resistance of a rectangular section:

Mr = Resistant moment.

Req

= Fiber reinforced concrete equivalent strength, considered that the section is homogeneously distributed and reinforced.

Sx = b.h2 = Modulus of strength of the provided rectangular section. 6

Here follows the comparison:

Figure 7.26 - Fiber reinforced section of Steel Deck.

Fiber reinforced concrete (C21) Dosage 25 kg/m3

Analysis for alternative in fiber reinforced concrete:

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To determine the equivalent resistance of fiber reinforced concrete there have been considered the results deriving from the Norm UNI11039, having as results of concrete characterization for resistance C25 and measurings 25 kg/m3 the parameters shown in the schedule above. Using as suggested value for a concrete C21, a first crack strength of 3,00 MPa, and maintaining a minimum of ductility of 61.5% for this measuring of fibers, being these data based on the characterizations of concretes according to RILEM.

N/mm

N/mm

N/mm

%

mm

mm

kg/m

kg/m

mm

mm

mm

mm

Nmm

kg/m

mm

Nmm

2

2

2

2

3

2

3

Measureunit

Mesh Fibers12,7/150 FF1 (1.00x50)

Comparison Traditional Reinforcement vs. Fibers Thickness = 80 mm

Mesh traction strength

Concrete with fibers bending traction strength (21 Mpa)

Concrete equivalent resistance (per 25 kg/m of fibers)

Ductility of concrete with fibers

Diameter of the mesh

Section of the mesh

Weight of the mesh/m2

Weight of the mesh /m

As = mesh resistant area

b = base of concrete section

h = concrete theoretical thickness

d = section usable thickness

M = Mesh Maximum Bending Moment

H = Proposed section thickness

M = Maximum Bending Moment of Concrete with fibers

3

3

Advised measuring

414,00

5,00

150,00

2,06

25,69

130,90

1.000,00

80,00

40,00

1.950.929

3,00

1,85

61,50

1.000,00

79,65

80,00

25

80

1.968.000

Characteristics

Table 7.2 - Mechanical comparison between rectangular section with traditional armor vs. rectangular section reinforced with fibers.

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7. Applications of fiber reinforced concrete: prefabricated elements.

The methodology previously shown, being based on the equivalence of resistant moments, would be a sufficient argument to prove the equivalence of the soultions, succeeding this way to obtain the ratification of the design.

Equivalent resistance vs. Fibers measuring(Concrete f´ck = 21 MPa)

Fibers measuring

Equi

valen

tres

istan

ce

..

.

Graphic 7.5 - Residual resistence vs. fibers measuring for concrete f´ck = 21 MPa.

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At present fibers are provided in different package formats, which can be chosen by the user, on the basis of the introduction system which can be applied under way.

MACCAFERRI offers two formats which cover in a flexible manner the different ways of introducing fibers into concrete. These formats are:

Format Cardboard BOX. The box can hold 20 kg of material. Its dimension and weight are designed to be handled by the workers, as much in the warehouse as in the yard. This format can be used for the manual introduction of fibers, or for batcher machines like.

8.1 - Equipments for the introduction of fibers into concrete.

Format BIG BAGS or Sacks. Big Bags are big sacks which can weigh between 500 and 1000 kg, de-pending on the product used. This format is of exclusive use for circular batchers like SF-500, DOSO 1.6 or DOSO 2.0, which have a maximum capacity of 1600 kg. This kind of equipment is used in fixed concrete mixing installations, where the time per cycle of concrete preparation is very strict and demands a greater autonomy.

Photo 8.1 - Box front view. Photo 8.2 - Box back view.

Photo 8.3 - EBox packaging in pallets with 1200 kg of material. Photo 8.4 - Loose fibers box content.

8 - Measuring equipments for Wirand® fibers.

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8. Measuring equipments for Wirand® fibers

Photo 8.5 - Big Bag example. Photo 8.6 - Big Bags in pallet in a concrete plant.

Photo 8.7 - Big Bags mobilization example. Photo 8.8 - Big Bags double packing format.

Equipments for fibers measuring.

In function of the different formats of material package, MACCAFERRI offers, as service, measuring equipments able to fit to concrete levels of production. The machines performances are variable in function of the fiber used.

DOSO BOX. Light, portable equipment, designed for works where fibers in box are used. This machine works with a pressure air system which conveys fibers through a pipe, up to the truck mixer mouth, in a fast and safe way. Its efficiency can reach 40-80 kg/min.

Photo 8.9 - Doso Box at the job site. Photo 8.10 - Doso Box assembly.

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Photo 8.11 - Doso Box assembly. Photo 8.12 - Doso Box in operation, dosing the fibers in the mixing truck.

SF500; DOSO 1.6; DOSO 2.0. They are fixed equipments for concrete mixing plants, they have a maximum capacity of 1600 kg. They are of exclusive use for BIG BAGS. They offer an efficiency up to 200 kg/min and can batch fibers in different ways:

- Directly to the mixing truck. In this case it’s necessary the construction of a framework to place the batcher at the height suitable for the unloading. This framework must be protected with a small roof under which it’s placed a stock of big bags to feed the equipment. The framework may be equipped with an electric or manual crane to lift the Big Bags and fill the batcher. In this case the equipment can be released by the concrete mixing plant, as the measuring will be carried out in the truck mixer after the other ingredients of the mixture.

- Unloading on aggregates conveyer belt. In this case the equipment is inside the concrete mixing plant and is placed so as to unload fibers on the conveyer belt of the aggregates of the plant. In this case, too, it’s necessary to protect the machine from bad weather and to equip it with lifting devices for Big Bags.

- Unloading on the hopper for mixer feeding (prefabricated). In this case the equipment is placed in the hopper load zone of the aggregates, which is at the end of the installation, so allowing to unload fibers together with aggregates. In this case, having light measuring, for volumes from 1 to 2 m3, other reserve equipments are used to guarantee the precision and homogeneity of the unloading. For the protection and lifting of big bags are valid the remarks previously expressed.

Figure 8.1 - Schematic example of Doso Box ready to load mixing trucks.

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Figure 8.2 - Schematic example of Doso Box ready to load in aggregates conveyer belt.

Figure 8.3 - Schematic example of Doso Box ready to load in the hopper for mixer feeding (precast).

Photo 8.13 - Dosage machine DOSO 2.0. Photo 8.14 - Dosage machine DOSO 1.6.

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8. Measuring equipments for Wirand® fibers

Photo 8.15 - Dosage machine DOSO SF-500 Photo 8.16 - Dosage machine DOSO SF-500 with crane for Big Bags shipment.

8.2 - Measuring systems of fibers for shot concrete.

The fibers measuring for shot concrete preparation can be carried out in different ways, from manual measuring up to industrialized one. The fibers commonly used in this kind of mixture are of loose format with a slimness ratio > 40 and with a length of about 30 – 35 mm.

Later on some examples of the different alternatives will be shown.

Manual alternative. Where boxes are emptied directly on the prepared mixture, both in truck mixers and in containers for conveyance, and on the aggregates conveyer belt in case of mixer installations.

Photo 8.17 - Concrete production in the mixing truck. Photo 8.18 - Slump verification before the fibers placement.

Photo 8.19 - Fibers placement in the mixing truck. Photo 8.20 - Fibers manual incorporation in aggregate conveyer belt.

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Photo 8.21 - Homogeneity mix verification after few minutes in the mixing truck.

Photo 8.22 - Slump verification after the fibers incorporation.

Photo 8.23 - Mixing truck during the discharge of the mix in the concrete bomb.

Photo 8.24 - During the shot concrete procedure.

Industrial alternative. In this case, depending on the investment available for the work, all machines offered by MACCAFERRI will be usable and the choice of the equipment will depend on the effective advantage of the customer. In this case it’s possible the use both of DOSO BOX and of the equip-ments DOSO 1.6 / DOSO 2.0 and SF-500.

Photo 8.25 - Mixing truck in approach of Doso, after the mix slump verification without fibers.

Photo 8.26 - Mixing truck in approach of Doso, after the slump mix verification without fibers.

Photo 8.27 - Fibers load in the mixing truck. Photo 8.28 - Slump mix verification with fibers. The mix is ready in few minutes of rotation in high speed by the mixing truck after the fibers incorporation.

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Photo 8.29 -In any cases is necessary the measure of temperature when it is working on places with high temperatures.

Photo 8.30 - Discharge of the mix about the equipment for shot concrete.

Photo 8.31 - Mixing trucks supplying the equipment for shot concrete.

Photo 8.32 - Automated equipment of shot concrete in conclusion phase of work.

8.3 - Measuring systems of fibers for the production of ashlars.

The measuring of fibers in the preparation of concrete for ashlars premanufacturing of ashlars, is a very particular case, in which the mechanized measuring is necessary for a strict control of the quantity introduced in the mixture.

Concretes for ashlars premanufacturing have got a very low workability and quantity of mixture between 1 e 2 m3.

The fibers measuring for one piece may vary between a minimum of 25 kg/m3 up to a maximum of 60 kg/m3. The fibers used in this kind of mixture have a ratio of aspect > 50 and length 50 mm, being mixtures with aggregates with maximum characteristic diameter of about 1” (25 mm).

The process of mixing is very fast, as it’s necessary to reach the optimal productivity in the premanu-facturing of such elements.

MACCAFERRI has designed a special system for ashlars premanufacturing installations, which is con-nected with the computer of the concrete mixing plant, so as to obtain a centralized control of the fibers measuring.

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8. Measuring equipments for Wirand® fibers

The concrete mixing plant adjusts the measuring of the various components of the mixture (cement, fibers, aggregates) which are poured into a hopper. The whole is introduced in the premixer, where water is added; the mixture is finally poured in the formwork. The accelerated seasoning process allows to obtain in 12 hours a piece ready to be conveyed and stocked.

The equipment is formed by:

- A batcher like SF 500 / DOSO 1,6 / DOSO 2.0.

- Second weighing machine (ex. Defibrator).

- A control system.

In the production process, the fibers are unloaded simultaneously to the aggregates into the reception hopper. The quantity of introduced fiber is preloaded and weighed on the second weighing machine which, in its turn, is fed by the circular batcher.

Here follows the description of the equipment used and the productive cycle:

Figure 8.4 - System general outline. Photo 8.33 - System general view.

Photo 8.34 - Doso and vibrator during the load of fibers in the conveyer belt.

Photo 8.35 - System general view, material discharge visualization at the conveyer belt

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Photo 8.44 - Precast segment after the curing, ready to be extracted of the form.

Photo 8.45 - Precast segment being turned in the position to be stored.

Photo 8.46 - Precast segment transported in the storage patio. Photo 8.47 - Precast segment in the storage patio.

8.4 - Measuring systems of fibers for floorings concrete.

In the measuring of fibers for floorings concretes, it’s possible to proceed in manual way or in indus-trialized way. In particular, in this kind of works, in case of industrialized production, the most applied measuring system is the use of DOSO BOX.

The technical remarks are identical to those of the previous cases.

In this case the mixtures are fluider than in premanufacturing. The fibers, depending on the kind of mixture will have a long or short format, in function of the chosen aggregates.

Here follows the example of a production process of concrete for flooring:

Photo 8.48 - Doso Box ready to supply the mixing truck. Photo 8.49 - Exit of the Doso Box feeder tube placed in the entrance of the mixing truck.

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Photo 8.50 - Doso Box ready to supply the mixing truck. Photo 8.51 - Worker introducing the fibers in the Doso Box.

Photo 8.52 - Fibers loading in the Doso Box entrance. Photo 8.53 - Fibers loading in the Doso Box entrance of where will be blower until the mixing truck.

Photo 8.54 - Mix aspect ready for application. Photo 8.55 - Concrete placement over the floor surface.

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8. Measuring equipments for Wirand® fibers

Photo 8.56 - Concrete placement. Photo 8.57 - Final finishing of the surface.

8.5 - Measuring systems of organic and polymeric fibers.

The introduction of organic or polymeric fibers into any concrete mixture, is normally carried out in manual way. The typical measuring for this kind of fibers go from 0.6 kg/m3 to 1.5 kg/m3.

This material is supplied in water-soluble bags which are directly thrown into the mixture; the pack-age will be melted by the water contained in the mixture. Its contents will spread in the mixture after a couple of minutes of mixing.

Here follows an example on the addition of these fibers:

Photo 8.58 - Format of the water-soluble packing of 0.6 kg. Photo 8.59 - Worker introducing the water-soluble bags in the mixing truck.

Information techniques detailed on equipment and systems of dosage displayed here could be found to follow.

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8. Measuring equipments for Wirand® fibers

The machine consists of, in its superior part, a cylindrical hopper and, in its inferior part, the framework including a fixed part of support and a mobile part provided with vibrant motors.

The inferior part is connected to the mobile one through antivibrant rubbers, inside the frame there are the load cells for obtaining the weigh of the fibers in the hopper.

The hopper has got inside a helical track; the track comes out, in the upper part, forming a pipe with rectangular section.

To complete the batcher described above (1), there is the electric board (2) and the control instru-ment (3).

8.6 - Circular batchers.

8.6.1 - Description of the machine.

The batcher helps to feed, in automatic way, with a flow of Wirand fibers, other machines or equip-ments, for instance the aggregates belt, batching a prearranged quantity of it measured in kg.

The batcher is connected and handled by the concrete mixing plant automizing the production of fiber reinforced concrete

8.6.2 - Aim.

There are three available models of circular batchers which are essentially distinguishable for the hopper diameter; moreover there may be different performances in relation to the motovibrators equipment:

Name Nominal diameter (mm)DOSO 1.6 1600SF500-S 1800DOSO 2.0 2000

8.6.3 - Typology.

A great quantity of fibers is received, during the machine load phase, in the central hopper space; this one, owing to the action of eccentric masses motovibrators, is put on vibration.

During the vibration the fibers arrange themselves in a uniform way on the hopper bottom, taking up also the lower part of the helical track.

8.6.4 - Principle of working.

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The flow capacity can be adjusted operating on the recording of motovibrators eccentric masses.

During the work phase (machine on vibration), the batcher controls the quantity (weight) of fibers come out through the load cells.

The batcher is provided with electric/electronic equipments which allow the control, the planning and the monitoring of the main operations of work.

The operations can be divided as follows:

Load operation

With this operation great quantities of fibers are introduced inside the batcher.

The supply takes place by using some Big Bags the handling of which is carried out by tackles or suitable equipments.

The fibers big bags, from 500 to 1000 kg, are placed on the batcher; later on, cutting their bottom, the fibers are let falling into the hopper central zone. The load phase may also be carried out by empting boxes of 20 kg of fibers inside the batcher.

The load process takes place with the machine not running, and must be carried out with such a frequency that the batcher isn’t too full or too empty.

To open the big bags bottom it’s necessary to keep at a certain safety distance not to be struck by the fibers; usually it’s necessary a raised platform around the batcher which may make easier this operation.

Planning operation

The plant operator must set up the recipe for the fibers measuring.The recipe consists of the quantity of fibers which must be taken out of the batcher.

Machine work phase

During this phase the machine is put on vibration; it can be activated by the operator in manual procedure, otherwise the concrete mixing plant will synchronize this phase with the other machines (ex. aggregates belt).

The length and the deactivation of this phase is handled by the batcher itself in function of the planned recipe or of possible further signals concerning the procedure of extracting fibers (ex. emergency stops, aggregates belt stop, etc.).

8.6.5 - Principle of use.

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(*) Weight varies in function of the kind of fiber used.

The pipe may be in a position mismatched of 45° to make easier the conveyance or the positioning in positions which otherwise wouldn’t be possible with the standard version.

The total bulks may then vary in function of the kind chosen.

The positioning of the standard batcher inside a container may take place in two different ways obtaining therefore different bulks.

8.6.6 - Technical data and main dimensions.

Before moving the batcher, it’s necessary to block the weighing devices.

Before using the batcher, it’s necessary to unblock the weighing devices.

For the details on blocking and unblocking operations see the machines use and maintenance hand-books

8.6.7 - Moving/conveyance.

23352100300028002100

1500-16002353758902000

1500 - 1400250 - 300

1770(1000 Kg) *

400 V50 Hz

6,75 Kw13,8 A

23352400-2700-

2300

22002065141023537067516001100 - 1000250 - 3001360(1000 Kg) *400 V50 Hz6,75 Kw13,8 A

27002700

2300

22002065141023537067516001100 - 1000250 - 3001360(1000 Kg) *400 V50 Hz6,75 Kw13,8 A

17002500

DOSO 1.61600

SF500-S1800

Standard

DOSO 2.02000

Standard

Nominal diameter

Overall heightOverall dimensionOverall dimensionWeightPipe inferior heightPipe protrusionPipe heightPipe widthPipe wheelbaseTrack external diameterTrack internal diameterTrack widthFeet wheelbase diameterApproximate maximum loadStrainFrequencyInstalled powerTotal current

HAB

(Kg)CScHcLcIc

DepDipLpDP

23002000-2450-

2300

22002065141023537067516001100 - 1000250 - 3001360(1000 Kg) *400 V50 Hz6,75 Kw13,8 A

17502300

2050185023501400

1737-17871400245375810180012002501840

(1000 Kg) *400 V50 Hz

-10 A

NOTICE: All dimensional values are expressed in mm.

2200206514102353706751600

1100 - 1000250 - 300

1360(1000 Kg) *

400 V50 Hz

6,75 Kw13,8 A

Rotated Rotated

8.6.8 - Necessary electric arrangement.

To use the batcher it’s necessary to arrange an electric connection with the requirements listed below. The machine is provided with some extensions which make easier the positioning of the machine itself and of its control instrument (STANDARD supply).

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Here below is listed the minimum necessary equipping to carry out the normal operations of machine installation and of performances adjusting through adjusting the eccentric masses

8.6.9 - Tools and implements necessary to the installation.

In case it’s necessary the cutting off of the machine electric board there’s available as OPTIONAL ON DEMAND a further extension to interpose between electric board and machine (20mt), in this case the extension supplied for instrument ED231 will be 20m long.

For the optional on demand or for personalized uses or configurations as for example the interaction with other machines it’s necessary to apply to the technical department in charge to get modalities, times and possible additional costs.

POWER SUPPLY

1 - Strain: 400 V 2 - Frequency: 50 Hz 3 - Installed power: 6,75 kW 4 - Total current: 13,8 A

MATERIAL SUPPLIED WITH THE MACHINE (STANDARD SUPPLY)

- Extension cable 30 m for supply. - Extension cable 30 m for control instrument ED231. - N°4 rings for the safety fixing of the support feet.

MATERIAL SUPPLIED WITH THE MACHINE (OPTIONAL ON DEMAND)

- Extension cable 30 m for supply. - Extension cable 2 m for control instrument ED231. - Extension cable 20 m for electric board. - N°4 rings for the safety fixing of the support feet.

N.221111-

DenominationOpen spannerOpen spannerOpen spannerOpen spannerHexagonal male spanner*Hexagonal male torquemetrical spannerEdge/Cruciform Screwdrivers

Measure32301713810-

Use

-

Hangers removal and feet adjustingFeet adjustingElectric board removalControl board removalMotovibrators lids removalMotovibrators masses adjusting

* Torquemetrical spanner calibration = 130 N.m (see schedule of the specific MOTOVIBRATORS handbook container in the section enclosures of the USE and MAINTENANCE handbook).

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Different operations and their necessary equipping will have to be carried out according to the USE AND MAINTENANCE HANDBOOK which is provided with the machine.

The batcher is normally placed near the aggregates belt of the concrete mixing plant, so that the protruding pipe of the machine from which fibers come out is placed above the belt, possibly in a central position.

It’s better to have a certain vertical distance between the pipe and the point of the belt where fibers will fall (1m.); considering that the pipe is at about 2m from the plane of support of the batcher itself, the considered point of the belt must be at about 1m. from the plane of support itself.

Often in the yard such position of the belt isn’t available, in these cases it’s advisable the building of frameworks in reinforced cement (plinths) or raised platforms, which can house the batcher. The exact position of the machine is then variable on the basis of the real yard configuration.

The batcher location is chosen by the person responsible of the plant, he will have also to arrange the building of possible platforms, necessary to the machine load operations, respecting all the safety regulations in force.

The machine must work under cover: then it’s also necessary to build roofing, if not present, to pro-tect the batcher from bad weather

8.6.10 - Positioning.

The batcher has got 4 rings which must be fixed to the framework on which it has been placed.

The rings have just the function of avoiding that the batcher may move too much in case of bad operation or of unstableness due to the vibration itself.

The rings must be placed around the machine feet and be fixed through welding or mechanical fixing using their fins. In the picture the kind of fixing is red highlighted.

Here follows schematically the use of plinths in reinforced cement.

The iron plates must be integral part of the plinths framework, on these plates the batcher feet will rest.

8.6.11 - Feet fixing.

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8. Measuring equipments for Wirand® fibers

On these plates it will also be possible to fix the 4 rings which will block the batcher feet.

The capacity of fibers flow can be varied within certain limits operating on the adjustment of mo-tovibrators masses.

The procedure of adjustment and the control of the masses way of rotation must be carried out respecting all the instructions of the USE AND MAINTENANCE HANDBOOK.

8.6.12 - Eccentric masses adjustment.

THE BATCHERS DON’T PROVIDE FOR WELDING OPERATIONS ON THE FIXED FRAMEWORK OR ON THE VIBRANT HOPPER.

If in case of necessity, maintenance, crack or something else had to be necessary a welding operation of electric kind on the machine it’s important to disconnect the 4 ground cables and the conveyance hangers which connect the hopper to the fixed framework.

If this doesn’t happen the electric welding operation will cause the crack of the weighing cells con-tained in the inferior part of the framework.

8.6.13 - Welding operations.

The fibers storage or warehousing (big bags or boxes) is of basic importance for fibers workability.

If this doesn’t happen correctly some rust might form and consequently there would be agglomerates of fibers difficult to disentangle.

It’s advisable:

- That fibers pallets are kept protected by bad weather; it’s suggested the warehousing in suitable covered structures and the use of waterproof lengths of cloth, moreover it’s better to protect fibers boxes from the moisture of the soil using wooden beds or something similar.

- To arrange pallets so that the fibers that have been in the yard for the longest time are used, following then the same chronological order of their delivery. This would avoid that fibers are used after a long time, with consequent protracted exposure to bad weather.

8.6.14 - Fibers storage.

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1 - Can the concrete mixing plant receive the batcher in a correct position?

2 - Can the plant staff build the necessary frameworks for the use of the batcher?

3 - Is it necessary to provide for material and configurations different from the standard ones, further extensions, different electric connections?

4 - Is the plant electric installation compatible with that of the machine?

5 - Shall the batcher be used in manual or automatic modality?

6 - Which batching settings is it preferable to prepare the batcher with?

7 - Is it necessary to train the plant staff on the use of the machine?

8 - Is the plant staff provided with the equipping for the moving, installation and maintenance of the machine?

9 - Is the plant arranged to receive in a suitable zone the fibers in big bags or boxes?

10 - Will the installation take place autonomously or is our service required?

If possible, it’s better to gather some photographic documents and a report on the plant and on the installation operation which have taken place.

8.6.15 - Information to gather for the correct configuration of the installation.

The pneumatic batchers help to introduce Wirand® fibers directly in the truck mixer, the quantity of fiber must be calculated previously using a number of pre-measured boxes (normally 20 kg each) in function of the required measuring and of the quantity of mixture in the mixer.

The machine simplifies the operations inside the yard; the operation of fibers batching may take place in manual or automatic way.

In the automatic way the batcher is connected and handled by the concrete mixing plant, further simplifying and automizing the production of fiber reinforced concrete.

8.7 - Pneumatic batchers.

8.7.1 - Aim.

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There are two available models of pneumatic batchers, they can be substantially distinguished de-pending on the principle of working of the first phase of disentangling, besides on the safety and practical ness level.

Name DOSOBOXSC99/2

8.7.2 - Typology.

A great quantity of fiber is received, during the machine load phase, in the vibrant hopper space for DOSOBOX or in the revolving drum for SC99/2; these devices allow to adjust the flow of fiber which will pass through the automatic circuit.

After this phase the fiber is shot along the pipe inside the suitably positioned mixer.

8.7.3 - Principle of working.

The use of the machine is easy: after positioning the machine inserting the pipe into the mixer hop-per, the load cycle starts; after a minimum starting time, the vibrant board or the drum begin to work allowing the operator to empty the boxes inside them.

It’s better to lead the mixer rotation to the maximum of turns to make easier the mixing of fibers during their insertion.

8.7.4 - Principle of use.

DOSOBOX conveys the fibers inside the mixer through pneumatic conveyance; the disentangling takes place through a vibrant pipe.

By increasing with a provided number of fibers boxes the required measuring will be obtained.

The superior safety level of the machine implies a minor velocity of installation and use in comparison with SC99.

Technical data

Conveyance bulk dimension:1600 x 1200 x 1500 (h) mm.

8.7.5 - DOSOBOX.

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The machine SC 99 too uses pneumatic conveyance to convey fibers inside the mixer; unlike DOSO-BOX, the disentangling takes place through a revolving drum.

The minor safety level of the machine implies a greater velocity of installation and use in comparison with DOSOBOX.

Technical data

Conveyance bulk dimension:2300 x 1100 x 1400 (h) mm.

Bulk dimension with assembled pipe:8000 x 1000 x 5000 (h) mm.

Weight: 750 kg.

Use strain: 400 V.Frequency: 50 Hz.Installed nominal power: 8 kW.

8.7.6 - SC99/2.

Bulk dimension with assembled pipe:5000 x 1200 x 5300 (h) mm.Weight: 1200 kg.

Use strain: 380 V.Frequency: 50 Hz.Installed nominal power: 10 kW.

The defibrator is normally used together with circular batchers; its function is that of “disentangling” the fibers which come out of the batcher and discharging them on a aggregates belt or into a hopper of the mixing plant. It’s then used for fibers with high aspect ratio, superior to 67.

There is a different appliance which considers it as second weighing phase in plants for ashlars.

The installation of the defibrator must be carried out just by specialized personnel, checking the cor-rect positioning and according to the safety regulations.

Owing to the presence of high risks and to the fact that its incorrect installation and use might gener-ate dangers for workers and damage other plant machines, it’s preferable not to use it.

8.7.7 - Special machines.Defibrator

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COMBINATION FOR DOUBLE WEIGHING (ex. ASHLARS)

In some plants it’s necessary to introduce small quantities of fibers in little time with high precision. These requirements are typical of ashlars manufacturing plants and wherever, anyway, the measuring required for each mixture is quantitatively limited. To satisfy these needs it’s necessary to combine and modify some of the standard machines; for instance a combination already used in several yards is arranged like that:

DOSO 2.0 with closing Kit DEFIBRATOR with cells and weighing instrument

The combination of these two modified machines allows to check the weight with some pre-load cycles, the quantity of pre-load fiber can be handled by the mixing plant or by the connected with the defibrator.

The concept is that of weighing in a static way a limited quantity of fiber inside the defibrator.

DOSO 2.0 feeds then the defibrator during the pre-load cycle; when it reaches the provided weight the defibrator drives the closing of the door assembled on the circular batcher preventing the not controlled fall of further fibers.

In a second phase the defibrator will feed the belt or the mobile hopper (skip) on which aggregates are conveyed, having already a fairly good mixing.

After this phase the cycle of pre-load will start.

For this kind of installations it’s necessary to know well all the features of the mixing plant, the cycle times and the quantities involved for concrete manufacturing.

In some plants it’s necessary to study particular and personalized machines to be able to obtain the introduction of the fiber in an optimal way.

Obviously the building of these machines is STRONGLY UNADVISED as it generates very high costs and log times of achievement.

The manufacturing of machines according to CE and to the consequent handbooks weighs heavily on the single machine causing high costs and times of starting up longer than usual.

Special machines are meant as vibrant pipes with or without weighing systems, conveyer belts or particular hoppers, here are some of the manufactured examples:

MONODIRECTIONAL PIPE WITH LOAD CELLS

With this machine it’s possible to feed the aggregates belt with a prearranged pre-load of fibers.

8.8 - Personalized machine.

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The pipe carries out the weighing of the pre-load statically and, differently from the defibrator, doesn’t carry out the further disentangling during the cycle of fiber introduction.

BIDIRECTIONAL PIPE WITH LOAD CELLS

With this machine it’s possible to feed with a prearranged pre-load two different points of fibers introduction.

The superior pipe carried out the pre-load weighing and during the introduction of fiber the switch and the inferior pipe will activate or not in order to feed the load mouth in which it’s necessary to convey the fibers in function of the controls set up in the control cab.

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ANTONIO GALLOVICH SARZALEJOStructural civil engineer graduated by the Central University of Venezuela (1992). It acted as promotion and technical manager in structural projects and seismicresistant rehabilitation, for the Maccaferri of Brazil (1999) was commercial end technical manager for the Maccaferri of Venezuela (2001). In the fibres for reinforcement sector of the concrete (2005) it worked as technical consulting for the Officine Maccaferri S.p.A. (Italy) e, currently, works as technical manager of product, fibres for reinforcement of the concrete, for the North America, Maccaferri Inc. (U.S.A.).

BRUNO ROSSI Structural civil engineer graduated by the University of Bologna, Italy (1992). For the company Officine Maccaferri S.p.A. it acted in the areas of in reinforced structures, of gravity retaining structures and hydraulic works (1996). It co-ordinated the research applied to the sector of active defense of the rock fall and currently he is the technical responsable and the research and development coordinator of fibers for concrete reinforcement in Officine Maccaferri S.p.A., Italy.

GIANFRANCO PERRIMining Engineering Doctor, acts as professor in the geomechanical, soil and rocks mechanical, geo-statistical and roads geotécnical areas since 1974; Head of the department of Mining Engineering in the Central Universidad of Venezuela, works with the Projects of Tunnels and Slopes (2007). It also exercise the functions of consulting and designing engineer, developing ample activity in the several geotechnical areas.

RALF WINTERBERGCivil engineer and doctor by the Ruhr-University of Bochum, Germany, with specialization in Structural Engineering and Durability (1992-98); complementary studies in the Essen Management Academy “Specialist Engineer for Project Management” (1999). It acted as technical manager responsable for the Research and Development, Technology and Engineering, Quality control, Marketing and Support Marketing in the Fibco GmbH (2003). Currently it develops the technician consultant function of Of-ficine Maccaferri S.p.A., Bologna, Italy; responsable for the fibres for the concrete reinforcement.

ROBERT EDUARDO PERRI ARISTEGUIETACivil engineer graduated by Metropolitan University of Caracas, Venezuela (2004); master in Direction of Construction and Real Estate Companies in the ETSAM of the Polytechnical Universidad of Madrid, Spain (2005); MBA Executive in the European School Business-oriented of Madrid, Spain (2006). Cur-rently it works as technical responsable of the fibres for concrete reinforcement department of the company A.Bianchini Ingeniero S.A., Barcelona, Spain.

9. Authors

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- Abaqus v. 6.4.1 (2003), “Theory manual”, Hibbitt, Karlsson e Sorensen, Pawtucket, Rhode Island (USA).

- ACI Committee 440. 1996. State-of-the-Art Report on Fiber Reinforced Plastic (FRP) for Concrete Structures (ACI 440R). ACI Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit, MI, 68 pp. - ACI Committee 544. 1982. State-of-the-Art Report on Fiber Reinforced Concrete (ACI 544.1R-82). Concrete International, May, Vol. 4, No. 5, pp. 9-30. - ACI Committee 544. 1988. Design Considerations for Steel Fiber Reinforced Concrete(ACI 544.4R-88). Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit, MI, 18 pp. - ACI Committee 544. 1990. State-of-the-Art Report on Fiber Reinforced Concrete. ACI Manual of Concrete Practice, Part 5, American Concrete Institute, Detroit, MI, 22 pp.

- ACI Committee 544. 1993. Guide for Specifying, Proportioning, Mixing, Placing, and Finishing Steel Fiber Reinforced Concrete. ACI Materials Journal, Jan-Feb, Vol. 90, No. 1, pp. 94-101.

- ACI SP 182 (1988), “Structural Applications of Fiber Reinforced Concrete,” American Concrete Institute, Farmington Hills.

- Ahmad S., Di Prisco M., Meyer C., Plizzari G.A. e Shah S.P. Eds (2004), “Fiber Reinforced Concrete: From theory to practice”, Proceedings of the International Workshop, Bergamo, 24-25 Settembre 2004, Starrylink, 222 pp.

- Al-Tayyib A. H. J. and Al-Zahrani M. M.. 1990. Use of Polypropylene Fibers to Enhance Deterioration Resistance of Concrete Surface Skin Subjected to Cyclic wet/Dry Sea Water Exposure. ACI Materials Journal, Jul-Aug, Vol. 87, No.4, pp. 363-370.

- Altoubat Salah A., Lange David A., - Early age Shrinkage and Creep of Fiber Reinforced Concrete for Airfield Pavement-Aircraft/Pavement Tecnology (229-243)

- Alwahab T. and Soroushian P.. 1987. Characterization of Fiber Force Collated Fibrillated Polypropylene Fibers and Their Application to Concrete. Research Report, Department of Civil and Environmental engineering, Michigan State University, 60 pp.

- Anderson W. E.. 1978. Proposed Testing of Steel-Fibre Concrete to Minimize Unexpected Service Failures. Testing and Test Methods of Fibre Cement Composites. RILEM Symposium, The Construction Press, Lancaster, England, pp. 223-232.

- Ashour S. A. and Wafa F. F.. 1993. Flexural Behavior of High Strength Fiber Reinforced Concrete Beams. ACI Structural Journal, May-Jun, Vol. 90, No. 3, pp. 279-287.

10 - References.

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10. References.

- Aufmuth, R.E. , Naus, D.J. & Williamson, G.R., Effect of aggressive environments on steel fiber reinforced concrete. Letter Report M-113, US Army Corps of Engineers, Construction Engineering Research Laboratory, Champaign, Illinois, 1974

- Balaguru P. N. and Ramakrishnan V.. 1986. Freeze-Thaw Durability of Fiber Reinforced Concrete. ACI Journal, May-Jun, Vol. 33, No. 3, pp. 374-382.

- Balaguru P. N. and Ramakrishnan V.. 1988. Properties of Fiber Reinforced Concrete: Workability, Behavior Under Long-Term Loading, Air-Void Characteristics. ACI Materials Journal, May-Jun, Vol. 85, No. 3, pp. 189-196.

- Balaguru P. N. and Shah S. P.. 1992. Fiber Reinforced Cement Composites. McGraw-Hill, New York, 1992, xii, 530 pp.

- Balaguru P. N., Narahari R., and Patel M.. 1992. Flexural Toughness of Steel Fiber Reinforced Con-crete. ACI Materials Journal, Nov-Dec, Vol. 89, No. 6, pp. 541-546.

- Balaguru P. N.. 1992. Fiber-Reinforced Rapid Setting Concrete. Concrete International, Feb, pp. 64-67.

- Banthia N. and C. Foy. 1989. Marine Curing of Steel Fiber Composites. Journal of Materials in Civil Engineering, May, Vol. 1, No. 2, pp. 86-96.

- Barr. B. 1987. Fracture Characteristics of FRC Materials in Shear. Fiber Reinforced Concrete Proper-ties and Applications. American Concrete Institute, Detroit, MI, pp. 27-53. (ACI SP-105)

- Bassan M., - Calcestruzzi Fibrosi: Tecnologie ed Applicazioni; Relazione Generale-seminario A.I.C.A.P. “calcestruzzi speciali” L’Aquila, 5-6 ottobre 1988;

- Batson G. B.. 1991. Fatigue Strength Toughness Indices of Fiber Reinforced Concrete. Durability of Concrete. Second International Conference, held in Montreal, Canada; Ed. by V.M. Malhotra; American Concrete Institute, Detroit, MI, Vol. 2, pp. 715-728. (ACI SP-126)

- Batson G., Ball C., Bailey L., and Hooks J.. 1972. Flexural Fatigue Strength of Steel Fiber Reinforced Concrete. ACI Journal, Nov, Vol. 69, No. 11, pp. 673-677.

- Baumann R.A. and Weisgerber F.E, “Yield line analysis of slab on grade”, ASCE Journal of Structural Engineering, 109(7), 1983, pp. 1553-1568.

- Bayasi Z. and Celik T.. 1993. Application of Silica Fume in Synthetic Fiber-Reinforced Concrete. Transportation Research Record, No. 1382, pp. 89-98.

- Bayasi Z. and Zeng J.. 1993. Properties of Polypropylene Fiber Reinforced Concrete. ACI Materials Journal, Nov-Dec, Vol. 90, No. 6, pp. 605-610.

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- Beckett D. - 1999, “A comparison of Thickness design methods for concrete industrial ground floors”, 4th International Colloquium on Industrial Floor, January 12-16.

- Bedard C., Carette G. C., and Malhotra V. M.. 1986. Development of Air-Entrained, High Strength Concrete: Mechanics Properties and Resistance to Freezing and Thawing. CSCE/CANMET International Workshop on Concrete for Offshore Structures, held on Sept. 10-11, 1986, St. John’s, Newfoundland, Canada, 23 pp.

- Bedard C.. 1992. Composite Reinforcing Bars: Assessing Their Use in Construction. Concrete Inter-national, Jan, pp. 55-59.

- Belletti B., Cerioni B. & Plizzari G.A., - Fracture in SFRC slabs on grade – Sixth RILEM Symposium on FRC – BEFIB 2004;

- Benaiche F. and Barr B.. 1989. Fracture Characteristics of High Strength Concrete and FRC materi-als. Fiber Reinforced Cements and Concretes: Recent Developments. International Conference, held on Sept. 18-20, 1989, University of Wales College of Candift, U.K.; Ed. by R.N. Swamy and B. Barr, Elsevier Applied Science, London, pp. 611-619.

- Bentur A.. 1989. Silica Fume Treatments as Means for Improving Durability of Glass Fiber Reinforced Cements. Journal of Materials in Civil Engineering, Aug, Vol. 1, No. 3, pp. 167-183. - Bergstorm S. G.. 1976. A Nordic Research Project on Fibre Reinforced, Cement Based Materials. Proceedings of RILEM Symposium on Fibre Reinforced Cement and Concrete, held September 1975, The Construction Press, Lancaster, England, Vol. 2, pp. 595-600.

- Budelmann H. and Rostasy F.S.. 1993. Creep Rupture Behavior of FRP Elements for Prestressed Con-crete – Phenomenon, Results and Forecast Models. Proceedings of ACI International Symposium on FRP Reinforcement for Concrete Structures, held March 1993, Vancouver, B.C., Canada, pp. 87-100.

- Cangiano, S., Cucitore, R. e Plizzari, G.A. (2003), “La normativa uni per la classificazione del calces-truzzo rinforzato con fibre di acciaio”, in Giornata IGF sul calcestruzzo ad alte prestazioni, Brescia, 16 Novembre 2001, Plizzari G.A. e di Prisco M. Eds., Starrylink, pp. 183-198.

- Cervenka, J., ‘Discrete crack modeling in concrete structures’, Ph.D. thesis, University of Boulder, Colorado, 1994.

- Chanvillard G. and Aitcin P-C.. 1990. Thin Bonded Overlays of Fiber Reinforced Concrete as a Method of Rehabilitation of Concrete Roads. Canadian Journal of Civil Engineering, Aug, Vol. 17, No.4, pp. 521-527. - Chanvillard G., Aitcin P-C., and Lupien C.. 1989. Field Evaluation of Steel Fiber Reinforced Concrete Overlay With Various Bonding Mechanisms. Transportation Research Record, No. 1226, pp. 48-56.

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- CIMITAN L., FAILLA C., SIGNORINI S., SONZOGNI F. & VIGLIENO-COSSALINO G., - Indagine sulla durabilità dei calcestruzzi rinforzati con fibre d’acciaio - 14° Congresso C.T.E., Mantova, 7-9 Novem-bre 2002

- Concrete and Aggregates. 1988. Annual Book of ASTM Standards, Part 04.02, ASTM, Philadephia, PA, 751 pp.

- Concrete Toughens Up. 1991. Materials Engineering, Jan, Vol. 102, p. 38.

- Craig, R.J., Decker, J., Dombrowski, L. Jr, Laurencelle, R. & Federovich J., Anelastic behaviour of reinforced fibrous concrete. J. Structural Engineering, ASCE, 113 (1978)802-17.

- Dave N. J.. 1991. Fatigue Performance of Fibre-Reinforced Cement Composite Concrete Beams. Durability of Concrete, Second International Conference, 1991, Montreal, Canada; Ed. by V. M. Malhotra; American Concrete Institute, Detroit, MI, Vol. 2, pp. 697-713. (ACI SP-126) - Di Prisco M. e Plizzari G.A. Eds (2003), “La meccanica della frattura nel calcestruzzo ad alte prestazi-oni”, Atti della giornata di studio IGF, Starrylink Editrice, 232 pp.

- Di Prisco M. e Toniolo G. Eds. (2000), “Structural applications of steel fibre reinforced concrete”, Proc. of the international workshop. Milano, 4 Aprile, CTE publ., 126 pp.

- Di Prisco M., F. Iorio, G. A. Plizzari - High Performance Steel Fibre Reinforced Concrete prestressed roof elements –– Bochum 2003;

- DI PRISCO M., FAILLA C., PLIZZARI G.A. & TONIOLO G., - “Il calcolo delle strutture in calcestruzzo rinforzato con fibre d’acciaio: La norma UNI”, , Giornate AICAP 2004, Verona, 26-29 Maggio 2004

- Di Prisco M., Felicetti R. e Plizzari G.A. Eds (2004), “BEFIB 2004”, “Proceedings of the 6th RILEM Symposium on Fibre Reinforced Concretes (FRC), RILEM PRO 39, 1514 pp.

- Di Tommaso A., - Le fibre di acciaio nei conglomerati cementizi-estratto dalla rivista ACCIAIO n° 2, 1996;

- Diotallevi P.P., Zarri F. & Marino R., - Comportamento di Calcestruzzi Ordinari e Leggeri anche Fibror-inforzati Soggetti a Cicli di Gelo e Disgelo: Confronto di Alcune Caratteristiche Meccaniche-Quaderni di Studi e Ricerche, settembre 1991, Calcestruzzi S.p.A.;

- Edington J., Hannant D. J., and Williams R. I. T.. 1974. Steel Fiber Reinforced Concrete. Paper No. CP 69174, Building Research Establishment, Garston, Waterford, England, 17 pp.

- El-Badry M. (Ed.). 1996. Proceedings of the 2nd International Conference — Advanced Composite Materials in Bridges and Structures. Montreal, Quebec, Canada, 11-14, Aug, 1996, 1027 pp.

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10. References

- Ezeldin A. S. and Balaguru P. N.. 1992. Normal and High Strength Fiber-Reinforced Concrete Under Compression. Journal of Materials in Civil Engineering, Nov, Vol. 4, No. 4, pp. 415-429.

- Ezeldin A. S. and Lowe S. R.. 1991. Mechanical Properties of Steel Fiber Reinforced Rapid-Set Ma-terials. ACI Materials Journal, Jul-Aug, Vol. 88, No. 4, pp. 384-389.

- Falkner H., Huang Z., and Teutsch M. - 1995, “Comparative Study of Plain and Steel Fiber Reinforced Concrete Ground Slabs”, Concrete International, 17 (1), 45-51.

- Fanella D. A. and Naaman A. E.. 1985. Stress-Strain Properties of Fiber Reinforced Concrete in Compression. ACI Journal, Jul-Aug, Vol. 82, No. 4, pp. 475-483.

- Fattuhi H.. 1987. SFRC Corbel Tests. ACI Structural Journal, Mar-Apr, Vol. 84, No. 2, pp. 119-123. - Ferrari P. & Giannini F., - 2. Ingegneria Stradale, Corpo Stradale e Pavimentazioni-ISEDI;

- Fondazione Politecnica per il Mezzogiorno D’Italia; Domenichini, Di Mascio, Giannatasio, Caliendo, Festa, Marchionna, Firmi, Molinaro, Paoloni– Modello di Catalogo delle Pavimentazioni Stradali, Tema n° 10 “Catalogo delle Pavimentazioni Stradali” a cura del C.N.R.- AIPCR;

- Fondazione Politecnica per il Mezzogiorno D’Italia; Domenichini, Di Mascio, Giannatasio, Caliendo, Festa, Marchionna, Firmi, Molinaro, Paoloni–Criteri di dimensionamento delle sovrastrutture di cata-logo, Tema n° 9 “Catalogo delle Pavimentazioni Stradali” a cura del C.N.R.- AIPCR;

- Fondazione Politecnica per il Mezzogiorno D’Italia; Sbacchi A., D’Andrea A., Cafiso F., Mussumeci G.–Calcestruzzi Cementizi, Tema n° 6 “Catalogo delle Pavimentazioni Stradali” a cura del C.N.R.- AIPCR;

- Franke L.. 1981. Behavior and Design of High-Quality Glass-Fiber Composite Rods as Reinforcement for Prestressed Concrete Members. Report, International Symposium, CP/Ricem/i Bk, Prague, 52 pp.

- Fritz C., Naaman A. E., and Reinhardt D.H.W.. 1992. Sifcon Matrix in RC Beams. Proceedings of the RILEM-ACI International Workshop, held June 23-26, 1991, Mainz, Germany; Ed. by H. W. Reinhardt and A. E. Naaman, E & FN Spoon, London, pp. 518-528.

- Gallovich, A. “Diseño de losas sobre terreno en concreto fibroreforzado, una realidad técnica de alto performance” Congreso Puertorriqueño del Concreto, San Juan Puerto Rico, Marzo 15, y 16 del 2006.

- GangaRao H. V. S., Altizer D. S., Vijay P. V., Douglass N., and Pauer R.. 1995. Thermoset Polymer Performance under Harsh Environments to Evaluate Glass Composite Rebars for Infrastructure Appli-cation. Paper Presented at the 1996 ACI Spring Convention, Denver, Colorado, Mar 14-19, 1995.

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10. References.

- Gasparini D. A., Verna D., and Abdallah A.. 1989. Post Cracking Tensile Strength of Fiber Reinforced Concrete. ACI Materials Journal, Jan-Feb, pp 10-15.

- Gerritse A. and Den Uijl J. A.. 1995. Long-Term Behaviour of Arapree. Proceedings of the Second International RILEM Symposium, held on Aug. 23-25, 1995, Ghent, Belgium; Ed. by L. Taerwe; pp. 57-66.

- Gettu, R., Barragan, B., Garcia, T., Ramos, G., Fernandez, C. e Oliver, R. (2004), “Steel Fiber Rein-forced Concrete for the Barcelona Metro Line 9 Tunnel Lining”, in BEFIB 2004, Proceedings of the 6th RILEM Symposium on FRC, Varenna (Italy), Sept. 20-22, RILEM PRO 39, 141-156.

- Gopalaratnam S. and Shah S. P.. 1987. Tensile Failure of Steel Fiber Reinforced Mortar. Journal of Engineering Mechanics, May, Vol. 113, No. 5, pp. 635-652.

- Gopalaratnam V. S., Shah S. P., and John R.. 1984. A Modified Instrumental Charpy Test for Cement Based Composites. Experimental Mechanics, Jun, Vol. 24, No. 2, pp. 102-110. - Hackman L. E., Farrell M. B., and O. O. Dunham. 1992. Slurry Infiltrated Mat Concrete (SIMCON). Concrete International, Dec, pp 53-56.

- Halpin J. C. and Tsai S. W.. 1969. Effects of Environmental Factors on Composite Materials. AFML-TR 67423, Jun, 53 pp.

- Halvorsen, G.T. Kesler, C.E. Robinson, A.R. & Stout, J.A., - Durability and physical properties of steel fiber reinforced concrete. Report No. DOT-TST 76T-21, US Department of Transportation, Federal Railroad Administration, Washington, DC, 1976, 73 pp.

- Hanna A. N., - Steel Fiber Reinforced Concrete Properties and Resurfacing Applications-Portland Cement Association (PCA), Research And Development Bulletin RD049.01P;

- Hannant D.J., - Fibre Cements and Fibre Concretes, John Wiley and Sons Ltd, Chichester, 1978, 219 pp.

- Hannant, D.J. & Edgington, J., - Durability of steel fibre concrete. In Fibre Reinforced Cement and Concrete, Proceedings, RILEM Symposium, The Construction Press, UK 1975, pp. 159-69

- Hannant, D.J., - Additional data on fibre corrosion in cracked beams and theoretical treatment of the effect of fibre corrosion on beam load capacity. In fibre Reinforced Cement and Concrete, Pro-ceedings RILEM Symposium, The Construction Press, UK 1975, pp. 533-8

- Hara T. and Kitada Y.. 1980. Shear Strength of Reinforced Concrete Corbels and Steel Fibers as Reinforcement. Transactions of the Japan Concrete Institute, Vol. 2, pp. 279-286.

- Hartmann Tim -Steel Fiber Reinforced Concrete-Department of Structural Engineering at the Royal

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- Institute of Technology (KTH) in Stockholm-Stockholm, may, 1999;Haynes, H., - Investigation of fiber reinforcement methods for thin shell concrete, Naval Civil Engi-neering Laboratory Port Hueneme, CA, N-979 Sept. 1968, pp.1-26

- Hillerborg A., Modeer M., Petersson P.E.: “Analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements”, Cement And Concrete Research, Vol. 6, pp. 773-782, 1976.

- Hoff G. C.. 1985. Use of Steel Fiber Reinforced Concrete in Bridge Decks and Pavements. Steel Fiber Concrete, US-Sweden Joint Seminar (NSF-STU), Stockholm, Jun, pp. 67-108.

- Hoff, G.C., - Durability of fiber reinforced concrete in a severe marine environment. In Katharine and Bryant Mather International Symposium on Concrete Durability, ACI SP-100, Vol. I, American Concrete Institute, Detroit, 1987, pp. 997-1041

- Houde J., Prezeau A., and Roux R.. 1987. Creep of Concrete Containing Fibers and Silica Fume. Fiber Reinforced Concrete Properties and Applications. American Concrete Institute, Detroit, MI, pp. 101-118. (ACI SP-105) - Hsu L. S. and Hsu C-T. T.. 1994. Stress-Strain Behavior of Steel-Fiber High Strength Concrete Under Compression. ACI Materials Journal, July-Aug, Vol. 91, No. 4, pp. 448-457.

- Ibukiyama S., Kokubun S., and Ishikawa K.. 1989. Introduction of Recent Thin Bonded Concrete Overlay Construction and Evaluation of Those Performances in Japan. Proceedings of the 4th Inter-national Conference on Concrete Pavement Design and Rehabilitation, held on April 18-20, 1989, Purdue University, West Lafayette, IN, pp.193-203.

- Iyer S. L. and Anigol M.. 1991. Testing and Evaluating Fiber Glass, Graphite and Steel Cables for Pretensioned Beams. Advanced Composite Materials in Civil Engineering Structures. Proceedings of the Specialty Conference, ASCE, Las Vegas, Feb, pp. 44-56.

- Johansen K.W., “Yield line theory”, William Clowes and Sons Ltd., London, 1962.

- Johnston C. D. and Carter P. D.. 1989. Fiber Reinforced Concrete and Shotcrete for Repair and Restoration of Highway Bridges in Alberta. Transportation Research Record, No. 1226, pp 7-16.

- Johnston C. D. and Zemp R. W.. 1991. Flexural Fatigue Performance of Steel Fiber Reinforced Con-crete – Influence of Fiber Content, Aspect Ratio and Type. ACI Materials Journal, Jul-Aug, Vol. 88, No. 4, pp. 374-383.

- Johnston C. D.. 1980. Properties of Steel Fiber Reinforced Mortar and Concrete. Proceedings of International Symposium on Fibrous Concrete (Cl-80). The Construction Press, Lancaster, England, pp. 29-47.

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10. References.

- Johnston C.D.. 1982. Definition and Measurements of Flexural Toughness Parameters for Fiber Reinforced Concrete. Cement, Concrete and Aggregates, Winter, Vol. 4, No. 2, pp. 53-60.

- Johnston, C.D., - Steel fiber reinforced mortar and concrete: A review of mechanical properties. In fiber Reinforced Concrete, ACI SP-44, American Concrete Institute, Detroit 1974, pp. 195-207

- Khajuria A., Bohra K., and Balaguru P.. 1991. Long-Term Durability of Synthetic Fibers in Concrete. Durability of Concrete. Second International Conference, held in Montreal, Canada; Ed. by V.M. Malhotra; American Concrete Institute, Detroit, MI, Vol. 2, pp. 851-868. (ACI SP-126) - Knoblauch, H., Manufacture and properties of steel fiber reinforced concrete and mortar with in-creasing fiber content, Part 2. Betonwerk und Fertigteil- Technique, 11 (1979) 683-91

- Kosa, K. & Naaman, A.E., - Corrosion of steel fibre reinforced concrete. ACI Materials J. (in press)

- Krenchel H. and Stang B.H.. 1988. Stable Microcracking in Cementitious Meterials. Second Interna-tional Symposium on Brittle Composites, held September 1988, BMI, Cedzyna, Poland, pp. 20-33

- Krstulovic-Opara N., Uang C-M., and Hagayeghi A.. 1994. The Use of High Performance Cement Composites for Seismic Repair and Rehabilitation. Proceedings of the ASCE Materials Engineering Conference on Infrastructure: New Materials and Methods for Repair, held November 14-16, 1994, San Diego, CA, pp 812-819. liD. R. Lankard and E. K. Shrader. 1983. Inspection and Analysis of Curl in Steel Fiber Reinforced Concrete Airfield Pavement. Bekaert Steel Wire Corp., Pittsburgh, 9 pp. - Kukreja C.B. - 1987, “Ultimate Strength of Fiber Reinforced Concrete Slabs”, in Proceedings of International Symposium on Fiber Reinforced Concrete, 16-19 dicembre, Madras, 1, 237-255.

- Lankard D. R. and Walker A. J.. 1975. Pavement Applications for Steel Fibrous Concrete. Transporta-tion Engineering Journal, Feb, Vol. 101, No. TE1, pp. 137-153.

- Li V. C., Backer S., Wang Y., Ward R., and Green E.. 1989. Toughened Behavior and Mechanisms of Synthetic Fiber Reinforced Normal Strength and High Strength Concrete. Fiber Reinforced Cements and Concretes: Recent Developments. International Conference, Sept. 18-20, University of Wales Col-lege, Cardiff, U.K.; Ed. by R.N. Swamy and B. Barr, Elsevier Applied Science, London, pp. 420-433.

- Li Victor C., Maalej Mohamed-Toughening in Cement Based Composites.Part II: Fiber Reinforced Cementitious Composites-Cement & Concrete Composites 18 (1996) 239-249, Elsevier Science Limited;

- Li Victor C., Stang Henrik, Zhang Jun, Fellow, ASCE-Experimental Study on Crack Bridging in FRC under Uniaxial Fatigue Tension- Journal of Materials in Civil Engeneering/February 2000;(105) Li Victor C.-Engineered Cementitious Composites (Ecc) –Tailored Composites Through Micro-mechanical Modeling-Fiber Reinforced Concrete: Present and the Future, Eds: N. Banthia, A. Bentur, A. Mufti, Canadian Society of Civil Engineers, 1997;

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10. References

- Li Victor C.-Large Volume, High-Performance Applications Of Fibers In Civil Engeneering (2000)-ACE-MRL, Departement of Civil and Environmental Engineering, University of Michigan, Ann Arbor, Michigan 48109;

- Liang R. Y. and Galvez E.. 1990. High Strength, High Denier Discrete Polymer Fiber in Cementitious Composites. Proceedings of the First Materials Engineering Congress, held Aug. 13-15, 1990, Denver, CO; Ed. by Bruce A. Suprenant, ASCE, New York, Vol. 2, pp. 894-902.

- Lim T. Y., Paramavisam P., and Lee S. L.. 1987. Analytical Model for Tensile Behavior of Steel Fiber Concrete. ACI Materials Journal, Jul-Aug, Vol. 84, No. 4, pp. 286-298.

- Limit T.Y., Paramasivam, P. & Lee, S.L., - Shear and moment capacities of reinforced steel-fibre-concrete beams. Magazine of Concrete Research, 39 (1987) 148-60

- Lin W. S. and Hsu T. C.. 1990. Uni-axial and Bi-axial Compressive Fatigue of Fiber Concrete. Pro-ceedings of the First Materials Engineering Congress, held on Aug 13-15, 1990, Denver,CO; Ed. by Suprenent; ASCE, New York, Vol. 2, pp.1172-1181.

- Maage, M., - Fibre bond and friction in cement and concrete. In Testing and Test Methods of Fibre Cement Composites, ed. R.N. Swamy. The Construction Press Ltd. Lancaster, 1978, pp. 329-36Malmberg B. and Skarendahl A.. 1978. Method of Studying the Cracking of Fibre Concrete Under Restrained Shrinkage. Testing and Test Methods of Fibre Cement Composites. RILEM Symposium, The Construction Press, Lancaster, England, 545 pp.

- Mangat P. S. and Azari A. M.. 1985. A Theory for the Creep of Steel Fibre Reinforced Cement Ma-trices Under Compression. Journal of Materials Science, pp. 1119-1133.

- Mangat, P.S. & Azari, M.M., - Influence of steel fibre and Stirrup reinforcement on the properties of concrete in compression members. Int. J. Cement Composites and Lightweight Concrete, 7 (1985) 183-92

- Mangat, P.S. & Azari, M.M., - Influence of steel fibre reinforcement on the fracture behaviour of concrete in compression. Int. J. Cement Composites and Lightweight Concrete, 6 (1984) 219-32

- Mangat, P.S. & Azari, M.M., - Theory of free shrinkage of steel fibre reinforced cement mortars. Materials Science, 14 (1984) 2103-94

- Mangat, P.S. & Gurusamy, K., - Steel fibre reinforced concrete for marine applications. In Proceedings 4th International Conference on Behaviour of Offshore Structures, Delft, Elsevier Science Publishers 1985, pp. 867-79

- Mangat, P.S. & Gurusamy, K., Corrosion resistance of steel fibres in concrete under marine exposure. Cement and Concrete Research, 18 (1988) 44-54

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10. References.

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Authors:Eng. Antonio Gallovich Sarzalejo

Eng. Bruno RossiEng. Gianfranco PerriEng. Ralf Winterberg

Eng. Roberto Eduardo Perri Aristeguieta

Co-authors:Eng. Bruno Marson

Eng. Gerardo FracassiEng. Ivan Masiero

Page 238: Manual beton armat cu fibre

F i b e r s a s S t r u c t u r a l E l e m e n t f o r t h eR e i n f o r c e m e n t o f C o n c r e t e .

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