Properties of Reinforced Concrete

8/3/2019 Properties of Reinforced Concrete

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Chapter 1

PROPERTIES OF

ECS 318


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building material can be formed into manyvaried shapes and sizes.

Steel provide tensile strength & shear strength

Concrete stron in com ression, rotects

steel, to give durability and fire resistance.

Concrete + steel = strong structure in both of

tensile and compression strength.


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. =

So, concrete structures need reinforcement tocarr tensile force b bond between the interface

of the two materials.

If the bond is not ade uate, the reinforcement

will not 100% functioned & to reassured theeffectiveness of both material, concrete must be

we compacte aroun t e re n orcement. Main bar normally ribbed-extra mechanical grip.


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From : Reinforced Concrete Design to Eurocode 2

Steel reinforcement resist the tensile

force. Concrete carry compression from

vertical load.

The structure must rovided ood reinforcement bondin toensure the cracks are restrained from opening, so that the

embedded steel continues to be protected from corrosion.


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-.

the structure.

stresses on a cross-section member must

the concrete & steel, and also the

cross-section.


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. . Very variable material Have a wide range of strengths and stress-strain curves.

From the fi ure above the curve is no lon er linear & concrete acts

more to plastic material. If the load remove during plastic range, the recovery would no

longer be complete & permanent deformation would remain.. .


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Concrete generally increases its strength withage.

Some code of practice allow the concrete

the concrete when it supports the design load. As for Eurocode, do not ermit the use of

strengths greater than 28-day value calculations. But, the modulus of elasticity may be modified.


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EC2 based on characteristic cylinderstrength fck.

Cube stren th ma be used for

compliance purposes, fck cube . -

day characteristic strength.

C35/45

Cylinder strength, 35N/mm2 Cube strength, 45N/mm2


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The modulus of elasticit can be define recisel

from the stress-strain curve although therelationship is not truly linear.

strain

E =stress

strain

E =stress

strain

E =stress

strain

E =

erna ve e n ons , = cmEcm , secant or static modulus. Measured for a

cylinder is loaded to 1/3 of mean control cubestress, fcm cube or 0.4 mean cylinder strength.Then cycled back to zero stress.


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This remove the effect of initial bedding inand minor stress redistributions in theconcrete.

The load is reapplied and the behavior will

of the line up to the specified stress is

k n h v l f r E . Dynamic modulus of elasticity, Ed is

measure in the laboratory.


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Secant modulus Ecm = (1.25Ed -19) kn/mm2

The actual value of E depends on many factorre ate to t e m x.

But, the general relationship is consider to existe ween e mo u us o e as c y an e

compressive strength.


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. .

sudden increase in strain (before yield point), nochange in stress.

After yield point, becomes plastic material

strain increases rapidly up to the ultimate value.


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High yield steel most commonly used asreinforcement.

N h v fini i l in m

show a gradual change from elastic to

Reduced ductility depending on the.

All materials have similar slope of the

.

2s


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1.3 SHRINKAGE AND THERMALM VEMENT

Reduction in volume occur when concrete

harden. The shrinkage is liable to cause cracking in.

But also contribute in improvise the bond

between concrete & steel reinforcement. Shrinkage begin as soon as the concrete is

mixed caused by water absorption from concrete& a re ate.

Also caused by evaporation of the water whichrises to the concrete surface.


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Thermal shrinkage may reduced by :

Use mix design with low cement content orsuitable cement replacement.

, , ec

Avoid rapid hardening & finely groundcemen .

Keep aggregate and mixing water cool. Use steel shuttering and cool with a water

spray.

Strike the shuttering early to allow the heatof hydration to dissipate.


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. Cree is the continuous

deformation of a member undersustain load.

many materials but practically

to concrete. ,design, ambient humidity,member cross-section, & age at

. Generally is when the membersubjected to axial compression.


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The characteristic of creep are :

Final deformation can be 3 to 4 times theshort-term elastic deformation.

The deformation is roughly proportionallyto the intensity of loading and to theinverse of the concrete strength.

The instantaneous elastic deformation willrecover when the load is removed. Theplastic deformation is not.

There is a redistribution of load betweenthe concrete and any steel present.


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.

design & constructed, are long lasting &should re uired little maintenance.

The durability influence by :

the ex osure conditions The cement type

The concrete quality

The cover to the reinforcement

The width of any cracks


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Concrete can be exposed to a wide range condition ;

, - , . The severity of the exposure governs the mix design

& minimum cover.

Concrete mix should be made from impervious &chemically inert aggregates.

Condition Type of concrete

Specialized soil condition Well-compacted concrete-+sulfate resisting cement

Hot whether exposure Concrete with high watercement ratio + retarder

Repeated freezing & thawingatmosphere

Concrete + air entrainmentadmixture


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Adequate cover prevent corrosive agents reaching thereinforcement through cracks & previous concrete.

exposure & quality of concrete.

Cover also functions to protect the reinforcement againsta rapid rise temperature and subsequent loss of strengthur ng a re.


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1.6 SPECIFICATIONS OF

MATERIAL

. .

Form & size of

Structural member

Strength?

Choose typeof concrete


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Concrete strength measured by crushingstrength of cubes or cylinder (from theconcrete mix).

The sample are cured and tested after 28da s.

The given strength identified based by its

C35/45

Cube strength, 45N/mm2Cylinder strength, 35N/mm2


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Choice of mix design & class of concrete also

a ec y exposure con ons ura y.

Example : structure exposed to corrosiveu w u u

a denser & higher class of concrete.

, .use in most structures but other cement type

Blast-furnace/sulfate resisting cement resistchemical attack

Low-heat cement reduce the heat of hydration Rapid-hardening cement when high early strength

.


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1.6.2 Reinforcing Steel

replaced both grade 250 and 460.

High-yield bars (grade 500) are manufacturedwith a ribbed surface/form of a twisted square to have inferior bond characteristic.

Ribbed high-yield bars are classified as :Class Spec

A -Small diameter (


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Floor slab, walls, shells & roads

Use welded fabric reinforcement thatsupplied in rolls and having a square or

rectangular mesh. Benefit : - lar e economic in detailin .

- reduced site labour cost of

.

- save time


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scheduling are specified in BS8666.

ar ypes are en e y e o ow ngcodes : H = high yield steel (HA,HB,HC)

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Properties of Reinforced Concrete