DESIGN OVERVIEW FOR RC MEMBERS STRENGTH · PDF fileOverview for RC Members Strengthened Using Near Surface Mounted FRP Composites pp. 373 ... Design, Strengthening, FRP, Composites,

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International Journal of Civil Engineering and Technology (IJCIET)Volume 8, Issue 7, JulyAvailable online at ISSN Print: 0976 © IAEME

DESIGN OVERVIEW FOR STRENGTH

ABSTRACTStrengthening of structures is a complex task. Different systems are used of which

using externamembers is well accepted technology. Near surface mounted (NSM) FRP presents an alternate way to improve flexural and shear strength of concrete structures. Though the method has been inpromising results. This paper is an attempt to give overview of existing research in this area, identify gaps of knowledge, outline direction for future research and provide designers with protocol Key wordsconcrete, nearCite this ArticleOverview for RC Members Strengthened Using Near Surface Mounted FRP Compositespp. 373http://www.iaeme.com/IJCIET/issues.

1. INTRODUCTA considerable number of structures that are presently in use have been constructed in the last 20-30 years. With time, some of these structures need to be upgraded due to deterioration caused over their period of use. The errors made while designing astructures also necessitates upgradation of these structures over time. In the last two decades fibre reinforced polymernumber of projects across the globe have demonstreinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP materials and techniques. FRP reinfo


International Journal of Civil Engineering and Technology (IJCIET)Volume 8, Issue 7, JulyAvailable online at http://www.iaeme.com/IJCIET/issues.ISSN Print: 0976-6308 and ISS

© IAEME Publication

DESIGN OVERVIEW FOR STRENGTH

MOUNTED FRP COMPOSIT

Sardar Vallabhbhai National Institute of Techn

Sardar Vallabhbhai National Institute of Technology, Surat,

ABSTRACT Strengthening of structures is a complex task. Different systems are used of which

using externally bonded FRP laminates for strengthening of reinforced and concrete members is well accepted technology. Near surface mounted (NSM) FRP presents an alternate way to improve flexural and shear strength of concrete structures. Though the method has been inpromising results. This paper is an attempt to give overview of existing research in this area, identify gaps of knowledge, outline direction for future research and provide designers with protocol Key words: Design, Strengthening, FRP, Composites, Reinforced and Preconcrete, near-surface mountedCite this ArticleOverview for RC Members Strengthened Using Near Surface Mounted FRP Composites. International Journal of Civil Engineering and Technology

373–384. http://www.iaeme.com/IJCIET/issues.

1. INTRODUCTA considerable number of structures that are presently in use have been constructed in the last

30 years. With time, some of these structures need to be upgraded due to deterioration caused over their period of use. The errors made while designing astructures also necessitates upgradation of these structures over time. In the last two decades fibre reinforced polymernumber of projects across the globe have demonstreinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP materials and techniques. FRP reinfo

http://www.iaeme.com/IJCIET/index.

International Journal of Civil Engineering and Technology (IJCIET)Volume 8, Issue 7, July 2017, pp.

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Publication

DESIGN OVERVIEW FOR STRENGTHE

MOUNTED FRP COMPOSIT

Ph.D Scholar, Applied Mechanics Department, Sardar Vallabhbhai National Institute of Techn

Professor, Applied Mechanics Department, Sardar Vallabhbhai National Institute of Technology, Surat,

Strengthening of structures is a complex task. Different systems are used of which lly bonded FRP laminates for strengthening of reinforced and concrete

members is well accepted technology. Near surface mounted (NSM) FRP presents an alternate way to improve flexural and shear strength of concrete structures. Though the method has been in promising results. This paper is an attempt to give overview of existing research in this area, identify gaps of knowledge, outline direction for future research and provide designers with protocol for rational implementation of technology.

Design, Strengthening, FRP, Composites, Reinforced and Presurface mounted

Cite this Article: Aditya N. Contractor and Dr. Sandip A. VasanwOverview for RC Members Strengthened Using Near Surface Mounted FRP

International Journal of Civil Engineering and Technology

http://www.iaeme.com/IJCIET/issues.

1. INTRODUCTION A considerable number of structures that are presently in use have been constructed in the last

30 years. With time, some of these structures need to be upgraded due to deterioration caused over their period of use. The errors made while designing astructures also necessitates upgradation of these structures over time. In the last two decades fibre reinforced polymer (FRP) materials have emerged as promising repair materials. A great number of projects across the globe have demonstreinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP materials and techniques. FRP reinfo

IJCIET/index.asp

International Journal of Civil Engineering and Technology (IJCIET)2017, pp. 373–384, Article ID: IJCIET_08_07

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Scopus Indexed

DESIGN OVERVIEW FOR ENED USING NEAR SURFA

MOUNTED FRP COMPOSITAditya N. Contractor


Dr.Sandip A. VasanwalaProfessor, Applied Mechanics Department,



members is well accepted technology. Near surface mounted (NSM) FRP presents an alternate way to improve flexural and shear strength of concrete structures. Though

practice only recently research in the field has yielded promising results. This paper is an attempt to give overview of existing research in this area, identify gaps of knowledge, outline direction for future research and provide

for rational implementation of technology.Design, Strengthening, FRP, Composites, Reinforced and Pre

surface mounted (NSM), reinforcement, bond, detailingAditya N. Contractor and Dr. Sandip A. Vasanw

Overview for RC Members Strengthened Using Near Surface Mounted FRP International Journal of Civil Engineering and Technology

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=7

A considerable number of structures that are presently in use have been constructed in the last 30 years. With time, some of these structures need to be upgraded due to deterioration

caused over their period of use. The errors made while designing astructures also necessitates upgradation of these structures over time. In the last two decades

(FRP) materials have emerged as promising repair materials. A great number of projects across the globe have demonstreinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP materials and techniques. FRP reinforcements are available in variety of shapes. They could

asp 373

International Journal of Civil Engineering and Technology (IJCIET)Article ID: IJCIET_08_07

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Indexed

DESIGN OVERVIEW FOR NED USING NEAR SURFA



Dr.Sandip A. VasanwalaProfessor, Applied Mechanics Department,






(NSM), reinforcement, bond, detailingAditya N. Contractor and Dr. Sandip A. Vasanw


asp?JType=IJCIET&VType=8&IType=7



(FRP) materials have emerged as promising repair materials. A great number of projects across the globe have demonstrated the use of externally bonded fibrereinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP

rcements are available in variety of shapes. They could

International Journal of Civil Engineering and Technology (IJCIET)Article ID: IJCIET_08_07


DESIGN OVERVIEW FOR RC MEMBERS NED USING NEAR SURFA


Ph.D Scholar, Applied Mechanics Department, Sardar Vallabhbhai National Institute of Technology, Surat,

Dr.Sandip A. Vasanwala Professor, Applied Mechanics Department,






(NSM), reinforcement, bond, detailingAditya N. Contractor and Dr. Sandip A. Vasanw





(FRP) materials have emerged as promising repair materials. A great rated the use of externally bonded fibre

reinforced polymer laminates for strengthening reinforced concretecritical to have sufficient knowledge about behaviour and applicability of different FRP


[email protected]

International Journal of Civil Engineering and Technology (IJCIET) Article ID: IJCIET_08_07_040


RC MEMBERS NED USING NEAR SURFA

MOUNTED FRP COMPOSITES

Ph.D Scholar, Applied Mechanics Department, ology, Surat,

Professor, Applied Mechanics Department, Sardar Vallabhbhai National Institute of Technology, Surat,




for rational implementation of technology. Design, Strengthening, FRP, Composites, Reinforced and Pre

(NSM), reinforcement, bond, detailing.Aditya N. Contractor and Dr. Sandip A. Vasanw




caused over their period of use. The errors made while designing and executing these structures also necessitates upgradation of these structures over time. In the last two decades


reinforced polymer laminates for strengthening reinforced concrete (RC) structures. It is critical to have sufficient knowledge about behaviour and applicability of different FRP


[email protected]


RC MEMBERS NED USING NEAR SURFACE

ES

ology, Surat, India

Sardar Vallabhbhai National Institute of Technology, Surat, India




Design, Strengthening, FRP, Composites, Reinforced and Pre-stressed .

Aditya N. Contractor and Dr. Sandip A. Vasanwala. Design Overview for RC Members Strengthened Using Near Surface Mounted FRP

International Journal of Civil Engineering and Technology, 8(7), 2017,



nd executing these structures also necessitates upgradation of these structures over time. In the last two decades


(RC) structures. It is critical to have sufficient knowledge about behaviour and applicability of different FRP


[email protected]


RC MEMBERS CE




stressed

Design Overview for RC Members Strengthened Using Near Surface Mounted FRP

, 8(7), 2017,


nd executing these structures also necessitates upgradation of these structures over time. In the last two decades

(FRP) materials have emerged as promising repair materials. A great rated the use of externally bonded fibre-

(RC) structures. It is critical to have sufficient knowledge about behaviour and applicability of different FRP


Aditya N. Contractor and Dr. Sandip A. Vasanwala

http://www.iaeme.com/IJCIET/index.asp 374 [email protected]

be circular or rectangular or strips made by pultrusion or fabrics made with fibres in one or at least two different directions used in externally bonding wet lay-up technology. The fibrous phase of these reinforcements is composed of carbon(C), glass(G) and aramid(A) while in most cases matrix phase fibres are held together by epoxy. High strength adhesives can be used to bind FRP materials to the exterior of concrete structures. FRP reinforcements can also be inserted into grooves cut into concrete cover of RC element by a technique called Near Surface Mounting(NSM) FRP. FRP reinforcements are bonded therein with appropriate grove filler (epoxy paste or cement grout).

The use of Near Surface Mounted FRP reinforcement for increasing flexural and shear strength of deficient reinforced and pre-stressed (RC and PC) members (Alkhrdaji et al. 1999, De Lorenzis et al. 2000) as well as strengthening unreinforced masonry walls (Tumialan et al. 2001) has gained popularity in recent decades. The various advantages compared to externally bonded FRP laminates include but not limited to the possibility of anchoring reinforcement into adjacent members, upgrading elements in their negative moment region with reinforcement not exposed to potential mechanical damage typical to floor or deck systems (Nanni et al. 1999). NSM FRP technique minimises surface preparation work. Since the use of primer and putty is not necessary the installation time after groove cutting is also minimised when compared to externally bonded FRP laminates. NSM reinforcement also finds application in seismic retrofitting of RC column-beam joints to either provide additional strength or ductility when moving the failure zone from column to beam (Prota et al. 2001). The aesthetics of the strengthened structure is virtually unchanged. Because of these advantages NSM FRP method is in many cases superior to externally bonded FRP method or used in combination with it. Researchers across the globe have become aware of the practical advantages of this method resulting in boom in research in this area. Against this background this paper provides a comprehensive review of existing research in this area, gaps in knowledge and outlines for further future research.

2. HISTORY OF TECHNOLOGY Early 1950s in Europe witnessed the use of NSM reinforcement for strengthening of RC structures. Because of excessive settlement of steel cage during construction an RC bridge in Sweden needed to be upgraded in its negative moment region in 1948. The task was accomplished by inserting steel reinforcements bars in grooves made in concrete surface and filling it with cement mortar (Asplund 1949). NSM reinforcement has recently been used to upgrade masonry structures to increase its ductility and tensile strength (Atkinsosn and Schuller 1992). The technology has emerged as an effective and economical means to repair and strengthen low-rise masonry buildings and arch bridges (Garrity 1995). The original black steel used at the onset of development has been replaced by stainless steel. Epoxy-based grouts have partially replaced cementitious grout that were used for embedding reinforcement. FRP bars today are prime choice because of their noncorrosive properties and the ability of tailoring bar stiffness to the needs of application. Epoxy-based pastes or latex-modified cement grouts can be used owing to their rapid setting and bond strength.

Design Overview for RC Members Strengthened Using Near Surface Mounted FRP Composites


Figure 1technology 2001) where FRP bars have been used to enhance both flexural and confinement capacity, for

silo strengthening (Emmons et al.)

Figure 3 bars were used to increase the bridge deck negative

Figure 5



Figure 1 Shows a recent application of NSM technology 2001) where FRP bars have been used to

nhance both flexural and confinement capacity, for silo strengthening (Emmons et al.)

Represents a similar case where NSM bars were used to increase the bridge deck negative

moment capacity (Warren 1998).

Figure 5 Shows the applica



hows a recent application of NSM technology 2001) where FRP bars have been used to


epresents a similar case where NSM bars were used to increase the bridge deck negative


hows the application of rectangularcrack on the soffit of a bridge deck (Casadei et al. 2003).


IJCIET/index.asp



epresents a similar case where NSM bars were used to increase the bridge deck negative


tion of rectangularcrack on the soffit of a bridge deck (Casadei et al. 2003).


asp 375


nhance both flexural and confinement capacity, for

Figure 2technology for upgrading a solid RC bridge deck

epresents a similar case where NSM FRP bars were used to increase the bridge deck negative

Figure 4strengthened in shear with carbon FRP bars used

as NSM reinforcement (Hogue et al., 1999).

tion of rectangular-section carbon FRP bars used to stitch a longitudinal crack on the soffit of a bridge deck (Casadei et al. 2003).


Figure 2 Illustrates the application of this technology for upgrading a solid RC bridge deck

(Alkhrdaji et al. 2000).

Figure 4 Shows the grooving of RC joists to be strengthened in shear with carbon FRP bars used


section carbon FRP bars used to stitch a longitudinal crack on the soffit of a bridge deck (Casadei et al. 2003).


[email protected]

llustrates the application of this technology for upgrading a solid RC bridge deck


hows the grooving of RC joists to be strengthened in shear with carbon FRP bars used


section carbon FRP bars used to stitch a longitudinal crack on the soffit of a bridge deck (Casadei et al. 2003).


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section carbon FRP bars used to stitch a longitudinal


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section carbon FRP bars used to stitch a longitudinal



3. DESIGN PHILOSOPHY The strength design approach using NSM FRP reinforcement for RC and PC members recommends use of strength reduction factors as given in ACI 318(1999). It is rather necessary to refer to this version of Building Code than 2008 edition to maintain consistency with design guides issued by ACI on the use of FRP for new construction and repair.

Equations presented in this paper are based on the principle of force equilibrium, strain compatibility and constitutive laws of materials. It is also important to refer to the “Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures” reported by ACI Committee 440.2R (2008), and the “Guide for the Design and Construction of Concrete Reinforced with FRP Bars” also reported by ACI Committee 440.1R (2006).

Table 1 Environment –reduction factor ( )

Exposure condition Fiber and resin type CE Interior exposure Carbon/epoxy 0.95 Glass/epoxy 0.75 Aramid/epoxy 0.85 Exterior exposure (bridges, piers & unenclosed parking garages)

Carbon/epoxy 0.85

Glass/epoxy 0.65 Aramid/epoxy 0.75 Exposure condition Fiber and resin type CE Aggressive environment (chemical plants & waste water treatment plants)

Carbon/epoxy 0.85

Glass/epoxy 0.50 Aramid/epoxy 0.70

The strengthening threshold imposed to guard the structure against collapse or failure of FRP system due to fire, vandalism, temperature elevation, repeated freeze-thaw cycles, vandalism and other factors should be calculated with great caution. Equation 1 describes the existing strength of the structure(ϕRn) to resist a level of load.

(ϕRn)existing= (1.2D + 0.85L)new (1)

Material properties of FRP reinforcement reported by manufacturers, such as ultimate tensile strength, typically do not consider long-term exposure to environmental conditions, and should be considered as initial properties. FRP properties to be used in all design equations are given as follows (ACI 440 2006 and 2008):

ffu = CEf*fu (2)

εfu = CEε*fu

where ffu and εfu are the FRP design tensile strength and ultimate strain considering the environmental reduction factor (CE) as given in Table 1, and CEf*

fuand CEε*fu represent the

FRP guaranteed tensile strength and ultimate strain as reported by the manufacturer. FRP design modulus of elasticity is the guaranteed value reported by the manufacturer.



4. FLEXURAL DESIGN

Figure 6 illustrates calculation guidance for flexural strengthening effect for rectangular section resulting from longmember. Following assumptions are used in design

a plane section before loading remains plane after loading

Tensile strength is neglected for concrete and its maximum usable compressive strain is 0

FRP reinforcement has a linear elastic behaviour upto failure

Perfect bond exists between FRP reinforcements and surrounding concreteStrength reduction approach follows

with low ductility is compensatedstrength is achieved by applying a factor of 0.70 to brittle elements and 0.90 to ductile elements. The strength reduction factor (

Here εMode of failure should be g

procedure presented in this paper involves selecting a given neutral axis depth (c) and a failure mode (i.e. selecting ε c = ε cu or ε f = ε fe); calculating the strain level in each material using strain compatibility; calculating the associated stress level in each material from its stress-strain relationship; and checking internal force equilibrium. If the internal force resultants do not equilibrate, the depth to the neutral axis is revised and repeated.

Whitney stress block approach (ACI 318 1999) can be used as given when concrete crushing controls failure. When FRP rupture or concrete delamination controls failure an appropriate nona rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et al. 1982).



4. FLEXURAL DESIGN

Figure 6

Figure 6 illustrates calculation guidance for flexural strengthening effect for rectangular section resulting from longmember. Following assumptions are used in design






Here εs and εy is the strain in reinforcing steel at ultimate and yielding respectively.Mode of failure should be g

procedure presented in this paper involves selecting a given neutral axis depth (c) and a failure mode (i.e. selecting ε c = ε cu or ε f = ε fe); calculating the strain level in each material

strain compatibility; calculating the associated stress level in each material from its strain relationship; and checking internal force equilibrium. If the internal force

resultants do not equilibrate, the depth to the neutral axis is revised and repeated.

Whitney stress block approach (ACI 318 1999) can be used as given when concrete crushing controls failure. When FRP rupture or concrete delamination controls failure an appropriate non-linear stressa rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et al. 1982).



4. FLEXURAL DESIGN

Ultimate internal strain and stress distribution for rectangular sections.

Figure 6 illustrates calculation guidance for flexural strengthening effect for rectangular section resulting from longitudinal FRP reinforcement mounted onto tension face of RC member. Following assumptions are used in design






∅ =

⎩⎪⎨

⎪⎧

0.70

is the strain in reinforcing steel at ultimate and yielding respectively.Mode of failure should be g



resultants do not equilibrate, the depth to the neutral axis is revised and

Whitney stress block approach (ACI 318 1999) can be used as given when concrete crushing controls failure. When FRP rupture or concrete delamination controls failure an

linear stress-strain relationship should be usea rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et


IJCIET/index.asp

4. FLEXURAL DESIGN


Figure 6 illustrates calculation guidance for flexural strengthening effect for rectangular itudinal FRP reinforcement mounted onto tension face of RC

member. Following assumptions are used in designa plane section before loading remains plane after loading




with low ductility is compensated with a higher reserve for strength. This high reserve of strength is achieved by applying a factor of 0.70 to brittle elements and 0.90 to ductile elements. The strength reduction factor (ϕ) to be used is given by equation 3(ACI 440 2008).

⎧ 0.90

70 + 0.20(ε

0.0050.70

is the strain in reinforcing steel at ultimate and yielding respectively.Mode of failure should be governed to arrive at nominal strength. The trial and error





strain relationship should be usea rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et

β = 2 −4


asp 377



member. Following assumptions are used in design a plane section before loading remains plane after loading



Perfect bond exists between FRP reinforcements and surrounding concreteStrength reduction approach follows the philosophy of ACI 318(1999).,

with a higher reserve for strength. This high reserve of strength is achieved by applying a factor of 0.70 to brittle elements and 0.90 to ductile

ϕ) to be used is given by equation 3(ACI 440 2008). for

ε − ε )005 − ε

for

70 foris the strain in reinforcing steel at ultimate and yielding respectively.

overned to arrive at nominal strength. The trial and error procedure presented in this paper involves selecting a given neutral axis depth (c) and a failure mode (i.e. selecting ε c = ε cu or ε f = ε fe); calculating the strain level in each material




strain relationship should be usea rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et

4 − tan

In







Perfect bond exists between FRP reinforcements and surrounding concretethe philosophy of ACI 318(1999).,


ϕ) to be used is given by equation 3(ACI 440 2008).for ε ≥ 0.005

for ε < ε

for ε ≤ εis the strain in reinforcing steel at ultimate and yielding respectively.

overned to arrive at nominal strength. The trial and error procedure presented in this paper involves selecting a given neutral axis depth (c) and a failure mode (i.e. selecting ε c = ε cu or ε f = ε fe); calculating the strain level in each material




strain relationship should be used to determine resultant stress or a rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et

tan

1 +


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Perfect bond exists between FRP reinforcements and surrounding concretethe philosophy of ACI 318(1999).,


ϕ) to be used is given by equation 3(ACI 440 2008).005

ε < 0.005

is the strain in reinforcing steel at ultimate and yielding respectively.overned to arrive at nominal strength. The trial and error





d to determine resultant stress or a rectangular stress block appropriate for holding particular level of strain in concrete should be used. Equation 4 and 5 gives parameters for such stress block (see Figure 6) (Todeschini et


[email protected]




Perfect bond exists between FRP reinforcements and surrounding concrete the philosophy of ACI 318(1999)., where a member


ϕ) to be used is given by equation 3(ACI 440 2008).

005

is the strain in reinforcing steel at ultimate and yielding respectively.overned to arrive at nominal strength. The trial and error



resultants do not equilibrate, the depth to the neutral axis is revised and the procedure




[email protected]


Tensile strength is neglected for concrete and its maximum usable compressive strain is 0.03

where a member with a higher reserve for strength. This high reserve of

strength is achieved by applying a factor of 0.70 to brittle elements and 0.90 to ductile ϕ) to be used is given by equation 3(ACI 440 2008).

is the strain in reinforcing steel at ultimate and yielding respectively. overned to arrive at nominal strength. The trial and error



the procedure





γ =.

(4)

Where, ε 1.71 (5)

tan (ε |ε ) Is computed in radians. The ultimate effective strain (ε ) to be used for FRP reinforcement is given as following.

ε = κ ε (6) Where κ is bond dependent coefficient meant to limit strain in FRP reinforcement in

order to prevent delamination or debonding. Crack formation is the primary reason for debonding or delamination. The end points of strengthening system which represent singular points can be vulnerable to debonding. The main failure modes tested in laboratory set-up are splitting of epoxy cover, cracking of concrete surrounding bar and pull-out of FRP bar. Experiments (De Lorenzis and Nanni 2002) show that κ is affected by surface properties of FRP bars, properties of epoxy paste, groove size and concrete tensile strength. Experimental value of κ ranges from 0.60 to 0.84. Future research should be directed towards generating more accurate method for predicting appropriate bond dependant factor. A value of κm=0.70 has been selected in the design example given in ACI 440(2008). This value is consistent with both experimental data (De Lorenzis and Nanni 2002) and the approach followed by ACI 440 (2008) when defining an equivalent strain reduction factor for externally bonded FRP laminates.

Nominal tension strain attained in concrete surrounding FRP bars can be expressed as

ε , = ε ≤ ε + ε (7)

Where d represents depth of FRP reinforcements as shown in Figure 6. Initial strain ε in equation 7 can be evaluated using elastic analysis of the existing

member considering all loads are present at the time of FRP installation. When concrete crushing controls failure first term ε of the equation should be used and when FRP is controlling the failure mode, the second term ε + ε should be used.

The moment capacity of the strengthened member assuming no compression in steel reinforcement can be calculated using equation 8.

M = A f d − + Ψ A f d − (8)

An additional reduction factor Ψ of 0.85 is recommended to take account for the novelty of FRP data and is not based on test data (ACI 440 2008). f and f are taken from equation 9.

f = E ε < f f = E ε , ≤ E ε (9)

5. SHEAR DESIGN For externally bonded FRP laminates the method to calculate nominal shear capacity of strengthened member using NSM bars is similar to that used in ACI 440(2008). The design approach here deviates from the standard equations. Equation 10 is applicable for NSM systems and the same strength reduction factor φ =0.85 suggested by ACI 318 is used. An additional reduction factor ψ f = 0.85 is applied to the contribution of NSM FRP reinforcement to the shear strength of the member, as previously suggested for flexural design.



ϕv = ϕ(v + v + Ψ v ) (10) Groove dimensions, substrate material quality, FRP rebar type and quality of bond

influence NSM FRP bars contribution to shear capacity (v ). Strain from bond-controlled failure and maximum strain threshold of 0.004 should be taken into consideration while calculating shear capacity (De Lorenzis and Nanni 2001a). Strain threshold is responsible for maintaining shear integrity of concrete (Khalifa et al. 1998) and avoiding shear cracks which compromises aggregate interlock mechanism.

Slope of the shear crack is assumed to be at 45degrees. It is also assumed that bond stress is constant along the effective length of FRP bar at ultimate. The shear strength provided by the NSM reinforcement can be determined by calculating the force resulting from the tensile stress in the FRP bars across the assumed crack, and it is expressed by Equation 11 for circular and rectangular bars respectively.

V = 2πd τ L ∘ Circular bars v ( ) ∘ Rectangular bars (11) where db is the nominal FRP bar diameter, a and b represent the cross-sectional dimension

for rectangular FRP bar, and τ b represents the average bond stress of the bars crossed by a shear crack. Ltot can be expressed as Ltot = ∑i Li. Here Li represents length of each single NSM bar crossed by a 45degree shear crack expressed as following.

L = ∝ ∝ i ≤ l . i = 1 …

lnet −∝ ∝

i ≤ l . i = + 1 … n

(12)

Here α is the slope of FRP bar with respect to longitudinal axis of member. s is the FRP bar spacing. lnet represents net length of FRP bar to account for cracking of concrete cover and installation tolerance as shown in Figure 8. lnet is given by equation 13.

l = l − (13)

Where lb is actual length of FRP bar and c is clear concrete cover of internal longitudinal reinforcement. It is to be noted that c does not necessarily need to be considered as clear concrete cover; Figure9 shows a T-shaped cross section where c represents a term to account for the development length of FRP bars.

The first limitation in Equation 12 takes into consideration bond as the controlling failure mechanism, and represents the minimum effective length of a FRP bar crossed by a shear crack. It is expressed by ⋅ or l − ⋅ depending on the value assumed by the term n.

n = ( ) (14)

Here n is taken as the smallest integer (e.g. n = 32/3 = 10.7 => n = 10), and leff represents the vertical length of lnet written as follows:

l = l sin α − 2c (15) Spacing of FRP shear reinforcement should not exceed lnet/2, or 600 mm (24 in).


The second limitation in equation 12, llimiting at 0.004 the maximum strain in FRP reinforcondition, ( Arectangular bars, respectively:

Where ETo prevent crushing of concrete, the total reinforcement contribution taken as the sum of

both steel and FRP reinforcement, should be limited based on the criteria given for steel alone in ACI 318, as suggested in Equation 17 for US and SI customary, respectively.


Figure 7

Figure 8

Figure 9

The second limitation in equation 12, llimiting at 0.004 the maximum strain in FRP reinforcondition, ( Ab(0.004Erectangular bars, respectively:

Where Ef represents Young’s modulus of FRP bars.To prevent crushing of concrete, the total reinforcement contribution taken as the sum of

both steel and FRP reinforcement, should be limited based on the criteria given for steel alone CI 318, as suggested in Equation 17 for US and SI customary, respectively.



Figure 7 Representation of bar lengths as used for shear capacity computation.

Figure 8 Relationship betwee

Figure 9 Shear strengthening of T

The second limitation in equation 12, llimiting at 0.004 the maximum strain in FRP reinfor

(0.004Ef)= πdrectangular bars, respectively:

l . =

represents Young’s modulus of FRP bars.To prevent crushing of concrete, the total reinforcement contribution taken as the sum of


V + V


IJCIET/index.asp

Representation of bar lengths as used for shear capacity computation.

Relationship betwee

Shear strengthening of T

The second limitation in equation 12, llimiting at 0.004 the maximum strain in FRP reinfor

)= πdbl0.004τb), l0.004

rectangular bars, respectively: l .

= 0.002 ⋅



≤8 f bd

0.66 f


asp 380


Relationship between and length of the NSM bar

Shear strengthening of T-shaped concrete cross

The second limitation in equation 12, l0.004 accounts for shear integrity of concrete by limiting at 0.004 the maximum strain in FRP reinfor

0.004 can be determined as follows for circular and = 0.001



bdf bd



and length of the NSM bar

shaped concrete cross

accounts for shear integrity of concrete by limiting at 0.004 the maximum strain in FRP reinforcement. From the force equilibrium

can be determined as follows for circular and

Rectangular bars

represents Young’s modulus of FRP bars. To prevent crushing of concrete, the total reinforcement contribution taken as the sum of



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shaped concrete cross-section.

accounts for shear integrity of concrete by cement. From the force equilibrium

can be determined as follows for circular and Circular bars

ngular bars

To prevent crushing of concrete, the total reinforcement contribution taken as the sum of both steel and FRP reinforcement, should be limited based on the criteria given for steel alone

CI 318, as suggested in Equation 17 for US and SI customary, respectively.

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section.


can be determined as follows for circular and Circular bars

(16)


CI 318, as suggested in Equation 17 for US and SI customary, respectively.

(17)

[email protected]


can be determined as follows for circular and

(16)


(17)



6. DETAILINGMinimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. The limit may locase, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of installation requirements rather than engimaximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that increasing groove size will increafailure. FRP reinforcement and concrete share similar bond properties with steel reinforcement. In addition, these bond properties also show dependence on FRP type, elastic modulus, surface defUppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is highly dependentsteel reinforcement ratio, reinforcement configuration, and type of loading. They also suggested that by increasing the internal steel reinforcement ratio, development length increases and decreases with increase of either concrete compressive and/or groove size.

Figure 11 shows the equilibrium condition of a FRP bar with an embedded length equal to its development length, lthe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the average bond stress can be expressed as τ

Via equilibrium following equations can be derived for circular and rectangular bars respectively.



6. DETAILINGMinimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. The limit may loose significance when rectangular bar wicase, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of installation requirements rather than engimaximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that increasing groove size will increafailure. FRP reinforcement and concrete share similar bond properties with steel reinforcement. In addition, these bond properties also show dependence on FRP type, elastic modulus, surface defUppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is highly dependent on strip dimensions, groove size, concrete and adhesive properties, internal steel reinforcement ratio, reinforcement configuration, and type of loading. They also suggested that by increasing the internal steel reinforcement ratio, development length

reases and decreases with increase of either concrete compressive and/or groove size. Figure 11 shows the equilibrium condition of a FRP bar with an embedded length equal to

its development length, lthe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the average bond stress can be expressed as τ

Via equilibrium following equations can be derived for circular and rectangular bars respectively.



6. DETAILING Minimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar.

se significance when rectangular bar wicase, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of installation requirements rather than engimaximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that increasing groove size will increafailure. FRP reinforcement and concrete share similar bond properties with steel reinforcement. In addition, these bond properties also show dependence on FRP type, elastic modulus, surface deformation and shape of FRP bar as studied by AlUppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is

on strip dimensions, groove size, concrete and adhesive properties, internal steel reinforcement ratio, reinforcement configuration, and type of loading. They also suggested that by increasing the internal steel reinforcement ratio, development length


its development length, ld. The force in the bar is resisted by the shear stressethe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the average bond stress can be expressed as τ

Figure 10

Figure 11

Via equilibrium following equations can be derived for circular and rectangular bars


IJCIET/index.asp

Minimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. se significance when rectangular bar wi

case, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of installation requirements rather than engimaximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that increasing groove size will increase bond strength. The effect is not visible in case of pullout failure. FRP reinforcement and concrete share similar bond properties with steel reinforcement. In addition, these bond properties also show dependence on FRP type, elastic

ormation and shape of FRP bar as studied by AlUppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is



. The force in the bar is resisted by the shear stressethe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the average bond stress can be expressed as τ

Figure 10 Minimum dimension of the grooves.

Figure 11 Transfer of force in an FRP


l ( .


asp 381

Minimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. se significance when rectangular bar wi

case, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of installation requirements rather than engineering. At the moment, there is dearth of data for maximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that

se bond strength. The effect is not visible in case of pullout failure. FRP reinforcement and concrete share similar bond properties with steel reinforcement. In addition, these bond properties also show dependence on FRP type, elastic




. The force in the bar is resisted by the shear stressethe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the average bond stress can be expressed as τ b = 0.5 τ max

Minimum dimension of the grooves.

Transfer of force in an FRP


)


Minimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. se significance when rectangular bar with large aspect ratio is used. In that

case, minimum groove size of 3.0a × 1.5b could be suggested (Figure 10) where a is the smallest bar dimension. In other cases, minimum groove dimension could be the result of

neering. At the moment, there is dearth of data for maximum dimensions of groove. Tests have been conducted using the abovementioned dimensions. When epoxy paste controls failure De Lorenzi and Nanni in 2002 proposed that





. The force in the bar is resisted by the shear stressethe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the

max.


Transfer of force in an FRP bar.



[email protected]

Minimum dimension of grooves should be kept at least 1.5 times the diameter of FRP bar. th large aspect ratio is used. In that




ormation and shape of FRP bar as studied by Al-Zahrani et al. 1996; Uppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is



. The force in the bar is resisted by the shear stressethe surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the


bar.



[email protected]





Zahrani et al. 1996; Uppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is



. The force in the bar is resisted by the shear stresses τ b acting on the surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the



[email protected]





Zahrani et al. 1996; Uppuluri et al. 1996; Gao et al. 1998. When NSM CFRP rectangular bars are used for strengthening RC beams Hassan and Rizakalla in 2002 found that the development length is



acting on the surface of the bar. Assuming a triangular stress distribution (Ibell and Valerio 2002), the




l ∗( )( . )

(18)

Hassan and Rizkalla (2002) suggested an expression for τmax when concrete crushing is the controlling failure mode. When the controlling failure mode is not known, a conservative value of τmax=3.5 MPa (0.50 ksi) is suggested.

7. CONCLUSIONS An overview of flexural and shear design of RC members strengthened with NSM FRP has been presented in this paper. The proposed procedure reflects the framework used in the two guides published by ACI (ACI 440.2R-08, 2008, and ACI 440.1R-06, 2006) with adjustment coming from experimental evidences. Near surface mounted reinforcement is a technique used globally for about half a century to enhance flexural capacity of existing RC and masonry structures. Future research should be directed to understand properties and quality of bond between FRP bars, bars, paste and concrete. Focus should be on understanding the effects of groove size especially when rectangular bars are used. Studies to understand shear strengthening of NSM bars are sure to prove a great boon.

REFERENCES [1] ACI Committee 318 (1999). Building Code Requirements for Structural Concrete (ACI

318-99) and Commentary (ACI 318R-2008), American Concrete Institute, Farmington Hills, Michigan, 391 pp.

[2] ACI Committee 440 (2008). Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (ACI 440.2R-08), American Concrete Institute, Farmington Hills, Michigan, 45 pp.

[3] ACI Committee 440 (2006). Guide for the Design and Construction of Concrete Reinforced with FRP Bars (ACI 440.1R-06), American Concrete Institute, Farmington Hills, Michigan, 42 pp.

[4] Alkhrdaji, T., Nanni, A., Chen, G. and Barker, M. (1999). “Upgrading the transportation infrastructure: solid RC decks strengthened with FRP”, Concrete International, American Concrete Institute, Vol. 21, No. 10, pp. 37-41.

[5] Alkhrdaji, T., Nanni, A. and Mayo, R., (2000). “Upgrading missouri transportation infrastructures: solid RC decks strengthened with FRP”, Transportation Research Record, No. 1740, pp. 157-169. (also available in: Proceedings, 79th Annual Transportation Research Board, Jan. 9-13, 2000, Washington, DC, CD-ROM version, paper 00-1177, 24 pp.)

[6] Al-Zahrani, M. M., Nanni, A., Al-Dulaijan, S. U. and Bakis, C. E. (1996). “Bond of FRP to concrete for bars with axisymmetric deformations”, Proceedings of the Second International Conference on Advanced Composite Materials in Bridges and Structures (ACMBS-II), Montreal, Canada, pp. 853-860.

[7] Asplund, S. O. (1949). “Strengthening of bridge slabs with grouted reinforcement”, Journal of the American Concrete Institute, Vol. 20, No. 6, pp. 397-406.

[8] Atkinson, R. H. and Schuller, M. P. (1992). “Development of injectible grouts for the repair of unreinforced masonry”, Proceedings of the Workshop on Effectiveness of Retrofitting of Stone and Brick Masonry Walls in Seismic Areas, Dept. of Struct. Engrg., Politecnico di Milano, Milan, Italy.

[9] Casadei, P., Galati, N., Parretti, R. and Nanni A. (2003). “Strengthening of a bridge using two FRP technologies”, Field Application of FRP Reinforcement: Case Studies, ACI



Convention, Boston, Sept. 27-Oct. 1, Rizkalla, S., and Nanni A., Editors, ACI Special Publication No. 215, American Concrete Institute, Farmington Hills, MI, pp. 219-237.

[10] De Lorenzis, L., Nanni, A. and La Tegola, A. (2000). “Flexural and shear strengthening of reinforced concrete structures with near surface mounted FRP bars”, Proceedings of the Third International Conference on Advanced Composite Materials in Bridges and Structures, Ottawa, Canada, pp. 521-528.

[11] De Lorenzis, L. and Nanni, A. (2001a). “Strengthening of reinforced concrete beams with near-surface mounted fiber-reinforced polymer bars”, Structural Journal, ACI, V. 98, No. 1, pp. 60-68.

[12] De Lorenzis, L. and Nanni, A. (2001b). “Characterization of FRP bars as near surface mounted reinforcement”, Journal of Composites for Construction, ASCE, Vol. 5, No. 2, pp. 114-121.

[13] De Lorenzis, L. and Nanni, A. (2002). “Bond between near surface mounted FRP bars and concrete in structural strengthening”, Structural Journal, ACI, Vol. 99, No. 2, pp. 123-133.

[14] Emmons, P., Thomas, J. and Sabnis, G.M. (2001). “New strengthening technology for blue circle cement silo repair and upgrade”, Proceedings of FRP Workshop US-AID, Cairo, Egypt.

[15] Gao, D., Benmokrane, B. and Tighiouart, B. (1998). Bond Properties of FRP Rebars to Concrete, Technical Report, Department of Civil Engineering, University of Sherbrooke, Sherbrooke, Quebec, Canada, 27 pp.

[16] Garrity, S. W. (1995). “Retro-reinforcement – a proposed repair system for masonry arch bridges”, Proceedings of the First International Conference on Arch Bridges, Bolton, UK, pp. 557-566.

[17] Hassan, T. and Rizkalla, S. “Investigation of bond in concrete structures strengthened with near surface mounted CFRP strips” (in press).

[18] Hogue, T., Cornforth, R.C. and Nanni, A. (1999). “Myriad convention center floor system reinforcement”, Proceedings of the FRPRCS-4, C.W. Dolan, S. Rizkalla and A. Nanni, Editors, ACI, Baltimore, MD, pp. 1145-1161.

[19] Ibell, T.J. and Valerio, P. (2002). “Shear strengthening of existing concrete bridges”, Proceedings of ICE Structures and Buildings, UK, in press.

[20] Khalifa, A., Gold, W. J., Nanni, A. and Abdel Aziz, M. I. (1998). “Contribution of externally bonded FRP to shear capacity of RC flexural member”, Journal of Composites for Construction, ASCE, Vol. 2, No. 4, pp. 195-202.

[21] MacGregor, J. G. (1997a). Reinforced Concrete: Mechanics and Design, Third Edition, Prentice-Hall, NJ, pp. 388-392.

[22] MacGregor, J. G., (1997b). Reinforced Concrete: Mechanics and Design, Third Edition, Prentice-Hall, NJ, pp. 215-218.

[23] Nanni, A., Alkhrdaji, T., Barker, M., Chen, G., Mayo, R. and Yang, X. (1999). “Overview of testing to failure program of a highway bridge strengthened with FRP composites”, Proceedings of Fourth International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures (FRPRCS-4), SP-188, C. W. Dolan, S. Rizkalla, and A. Nanni, Eds., American Concrete Institute, Farmington Hills, Mich., pp. 69-75.

[24] Prota, A., Nanni, A., Manfredi G. and Cosenza E. (2001). “Design criteria for RC beam-column joints seismically upgraded with composites”, Proceedings of the International Conference on FRP Composites in Civil Engineering - CICE 2001, J.-G. Teng, Ed., Hong Kong, China, Vol. 1, pp. 919-926.



[25] Renato Parretti and Antonio Nanni (2004). “Strengthening of RC members using Near-Surface Mounted FRP composites: Design Overview”, Advances in Structural Engineering Vol.7, No 5 2005.

[26] Todeschini, C., Bianchini, A. and Kesler, C. (1982). “Behavior of concrete columns reinforced with high strength steels”, ACI Journal, Proceedings, Vol. 61, No. 6, pp 701-716, November-December.

[27] Tumialan, G., Morbin, A., Nanni, A. and Modena, C. (2001). “Shear strengthening of masonry walls with FRP composites”, COMPOSITES 2001 Convention and Trade Show, Composites Fabricators Association, October 3-6, Tampa, FL, CD-ROM, 6 pp.

[28] Uppuluri, V. S., Bakis, C. E., Nanni, A. and Boothby, T. E. (1996). “Analysis of the bond mechanism in FRP reinforcement bars: the effect of bar design and properties”, Proceedings of the Second International Conference on Advanced Composite Materials in Bridges and Structures (ACMBS-II), Montreal, Canada, pp. 893-900.

[29] Warren, G. E. (1998). “Waterfront repair and upgrade”, Advanced Technology Demonstration Site No. 2: Pier 12, NAVSTA San Diego, Site Specific Report SSR-2419-SHR, Naval Facilities Engineering Service Center, Port Hueneme, CA. Whitney, C. S. and Cohen, E. (1956). “Guide for the ultimate strength design of reinforced concrete”, ACI Journal, Proceedings, Vol. 53, November, pp. 455-475.

[30] Prathamesh Dingorkar and Ayush Srivastava, Retrofitting–Comparative Study of RC Jacketing and FRP Wrapping. International Journal of Civil Engineering and Technology, 7(5), 2016, pp.304–310.

[31] N. Sundar, P. N. Raghunath and G. Dhinakaran, Flexural Behavior of RC beams with Hybrid FRP Strengthening. International Journal of Civil Engineering and Technology, 7(6), 2016, pp.427–433

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