北京化工大学：《材料导论》课程阅读材料（复合材料）Application_of_polymer_in_civil_construction-_A_general_review

Available online at www.sciencedirect.com ScienceDirect COMPOSITE STRUCTURES ELSEVIER Composite Structures 84(2008)114-124 www.clsevicr.com/locatc/compstruct Application of polymer composites in civil construction:A general review Sandeep S.Pendhari,Tarun Kant",Yogesh M.Desai Deparment of Cicil Engineering.Indian Institute of Techmology Bombay.Powai.Mumbai 40076.India Available online 12 July 2007 Abstract remrkre made lon pbrrof Keyord:FRPC:CFRPC;GFRPC:AFRPC:Rehabilitation:Strengthening 1.Introduction have presented a summary of applications of FRPC mate- vil eng ring whe Advanced co in ae anded use and a dustri the past fewdecades(rds)ueothroodn Use of FRPC sheets for strengthening and rehabilitation neering properties such as high specific strength and stiff- of concrete structures has attracted considerable interest ness,lower density.high fatigue endurance,high damping [9-12]First applications of composites were in the form the cnon),etc of rebars ind structural sha Later, ntial of o the rder we material for many problems associated with the deteriora. for retrofitting of concrete columns [14]. tion of infrastructures.Over the last decade,an increase in FRPC are available in the form of rods,grids,sheets the application of FRPCs has been seen in construction and winding stra Review ol ture up to 1996 can eir gde engineering properte nother genera conventional steel in reinforced concrete structures du onstruction was。 nted by Bakis et al.[161.The continuing drop in the cost of FRPC materials.Various divided the whole review into structural shapes internal aspects of FRPC materials including guidelines for selec- reinforcement,externally bonded reinforcement,bridge. ionafDoAaercadheires8 concrete have been standards and des.A review on shear strength ing o lighted and toet al. cussed by Karbhari [3)Einde et al.[4]and Bank et al.[5] for FRPC have been presented recently by Lu et al.[19]and review g of beam-column joints with FRPC can be 7Elsevier Ltd.All rights reserved

Application of polymer composites in civil construction: A general review Sandeep S. Pendhari, Tarun Kant *, Yogesh M. Desai Department of Civil Engineering, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India Available online 12 July 2007 Abstract Different applications of fiber reinforced polymer composites (FRPCs) for external strengthening in civil construction are reviewed in this paper. Experimental as well as analytical and numerical research contributions have been focussed in the review. The main structural components such as beams, columns and beam-column joints, have been reviewed and structural behavior of each component is dis￾cussed briefly. Finally, general concluding remarks are made along with possible future directions of research. 2007 Elsevier Ltd. All rights reserved. Keywords: FRPC; CFRPC; GFRPC; AFRPC; Rehabilitation; Strengthening 1. Introduction Advanced composite materials have found expanded use in aerospace, marine and automobile industries during the past few decades (1960 onwards) due to their good engi￾neering properties such as high specific strength and stiff- ness, lower density, high fatigue endurance, high damping and low thermal coefficient (in fiber direction), etc. Recently, civil engineers and the construction industry have begun to realize potential of composites as strengthening material for many problems associated with the deteriora￾tion of infrastructures. Over the last decade, an increase in the application of FRPCs has been seen in construction industry because of their good engineering properties. Fur￾ther, these are being considered as a replacement to the conventional steel in reinforced concrete structures due to continuing drop in the cost of FRPC materials. Various aspects of FRPC materials including guidelines for selec￾tion of polymer adhesives for concrete have been high￾lighted by ACI Committee-503 [1] and Uomoto et al. [2]. Issues related to selection of materials have also been dis￾cussed by Karbhari [3]. Einde et al. [4] and Bank et al. [5] have presented a summary of applications of FRPC mate￾rial in civil engineering whereas general design guidelines for FRPC application can be found in Bakht et al. [6], ACI Committee 440 [7] and Nanni [8]. Use of FRPC sheets for strengthening and rehabilitation of concrete structures has attracted considerable interest [9–12]. First applications of composites were in the form of rebars and structural shapes. Later, FRPC laminates were used for strengthening of concrete bridge girders by bonding them to the tension face of girder [13] as well as for retrofitting of concrete columns [14]. FRPC are available in the form of rods, grids, sheets and winding strands. Review of literature up to 1996 can be found in ACI Committee 440 [15]. Another general review on class of materials including FRPCs used in civil construction was presented by Bakis et al. [16]. They divided the whole review into structural shapes, internal reinforcement, externally bonded reinforcement, bridge, standards and codes. A review on shear strengthening of RC beams with FRPCs was done by Deniaud and Cheng [17], Bousselham and Chaallal [18]. Review related to the bond-slip model for FRPC sheet/plate bonded to concrete have been presented recently by Lu et al. [19] and review for upgrading of beam-column joints with FRPC can be found in Engindeniz et al. [20]. A large volume of literature 0263-8223/$ - see front matter 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2007.06.007 * Corresponding author. Tel.: +91 22 2576 7310; fax: +91 22 2576 7302. E-mail address: tkant@iitb.ac.in (T. Kant). www.elsevier.com/locate/compstruct Available online at www.sciencedirect.com Composite Structures 84 (2008) 114–124

S.S.Pendhari et al.Composite Stuctures 84(2008)114-124 now 2.1.1.Flex e up to Jury 20 exura The main objectives of the paper are to classify the avail- portion of elements in tension.with fibers parallel to the able literature(analytical/experimental)and to discuss the principal stress direction.If fibers are placed perpendicula varous parameters such as hber type,thicknes cracks,a large increase in strength and stiffnes references for details of parameters and mathematical research has been conducted for strengthening of RC models mswith glass.carbon or aramid FRPC 2.Repair and rehabilitation of structural elements shown that nearly 40%strength enhancement is possible or RC beams strengthenec with glass fiber reinforced orating structures to se polymer PC aroun ner omposites (CFRPC).In addition to the fiber from environmental exposure,inadequate design,poor flexural performance of strengthened RC beams is affected quality construction and a need to meet current y era rs such as modulus elasticity ol FR ,T381 gth of laminate [531 throughout the world.Recent experimental and analytical of main and shear reinforcement [54),number of FRPC research have monstrated that the use of composit ayers [40)level of loading [55)FRPC configuration em retro 6,57 h and cover [58]damage and loa the traditional means FRPC material has relatively low modulus of elasticity Historically, composites were first used as flexural nd linear stress-strain relation up to rupture with no de strengthening for e poin stren eams generall and unreinforced masonry walls (14]against ossible earth ritte failure mode 60.61 EfTect of reinforce ment rati quake forces.Apart from strengthening of bridge girders. on cracking moment,crack spacing, cracking patterns alls,composit s are als used in bridge nd crac experimentally cks and ir e stay al. inte in the [62).A variety of 631 to measure ductility because definition of ductility for stee 2.1.Strengthening of RC beams by using FRPC FRPeo ete beam an not be directly applied to the strengthene One of the most popular techniques for strengthening of ow ductility.Spadea et al.36]and Benc cardino et al 164 RC beams has involved the use of external epoxy-bonded ave suggested anchorage 122,2 It has been demonstrated expermer ich is not affed ling rat a ith this 42 ally technique is simple,cost-effective and efficient.However it was found that it s affers from a serious problem of dete t al.[67]that ap beams can be and con phase du eorsio up to with the help o tally tha nique involves construction of steel iackets which is a eective from strength,stiffess and ductility consider ve time consuming To l the was replaced by corrosion resistant and light-weight FRPC ated fastening system was used by Lamanna et al.[69]in plates.FRPC help to in ulity with xperiment al study by considering different fasters The tec que was repor to be placement of fibers. requ method also increased ductility over the conventionall

now exists on applications of FRPCs in construction indus￾try. However, literature up to July 2005 is considered here for general classification. The main objectives of the paper are to classify the avail￾able literature (analytical/experimental) and to discuss the effects of various parameters such as fiber type, thickness, fiber angle, concrete strength, etc. Discussion is kept on a descriptive level and reader is advised to refer to the cited references for details of parameters and mathematical models. 2. Repair and rehabilitation of structural elements Majority of rehabilitation works consist of repair of old deteriorating structures, damage due to seismic activities and other natural hazards. Structural strengthening is also required because of degradation problems which may arise from environmental exposure, inadequate design, poor quality construction and a need to meet current design requirement. Therefore, structural repair and strengthening has received much attention over the past two decades throughout the world. Recent experimental and analytical research have demonstrated that the use of composite materials for retrofitting existing structural components is more cost-effective and requires less effort and time than the traditional means. Historically, composites were first used as flexural strengthening materials for reinforced concrete (RC) bridges, as confining reinforcement for RC columns [21] and unreinforced masonry walls [14] against possible earth￾quake forces. Apart from strengthening of bridge girders, columns and walls, composites are also used in bridge decks and in cable stayed bridges. Strengthening of beams, columns and beam-column joints are discussed in the sequel. 2.1. Strengthening of RC beams by using FRPC One of the most popular techniques for strengthening of RC beams has involved the use of external epoxy-bonded steel plates [22,23]. It has been demonstrated experimen￾tally that flexural strength of a structural member can increase by about 15% with this technique. Steel bonding technique is simple, cost-effective and efficient. However, it was found that it suffers from a serious problem of dete￾rioration of bond at the steel and concrete interphase due to corrosion of steel. Other common strengthening tech￾nique involves construction of steel jackets which is quite effective from strength, stiffness and ductility consider￾ations. However, it increases overall cross-sectional dimen￾sions, leading to increase in self-weight of structures and is labour intensive. To eliminate these problems, steel plate was replaced by corrosion resistant and light-weight FRPC plates. FRPCs help to increase strength and ductility with￾out excessive increase in stiffness. Further, such material could be tailored to meet specific requirements by adjusting placement of fibers. 2.1.1. Flexural behavior of RC beams strengthened by FRPC Flexural strengthening of RC beams using composites can be provided by epoxy bonding of FRPC plate to the portion of elements in tension, with fibers parallel to the principal stress direction. If fibers are placed perpendicular to cracks, a large increase in strength and stiffness is achieved compared to situation where fibers are placed oblique to the cracks [24,25]. Considerable experimental research has been conducted for strengthening of RC beams with glass, carbon or aramid FRPCs to investigate serviceability, strength enhancement, cracking patterns and failure-modes, etc. [26–52]. Literature review has shown that nearly 40% strength enhancement is possible for RC beams strengthened with glass fiber reinforced polymer composite (GFRPC) whereas around 200% strength enhancement is achieved with carbon fiber poly￾mer composites (CFRPC). In addition to the fiber type, flexural performance of strengthened RC beams is affected by several factors such as modulus of elasticity of FRPC and its center of gravity location relative to the neutral axis [53], width of laminate [38], length of laminate [53], amount of main and shear reinforcement [54], number of FRPC layers [40], level of loading [55], FRPC configuration [56,57], concrete strength and cover [58], damage and load￾ing condition [43,59], etc. FRPC material has relatively low modulus of elasticity and linear stress–strain relation up to rupture with no def￾inite yield point. As a result strengthened beams generally exhibit large deflection, wide as well as closer cracks and brittle failure mode [60,61]. Effect of reinforcement ratio on cracking moment, crack spacing, cracking patterns and crack width was experimentally investigated by Masmoudi et al. [62]. A variety of indices including defor￾mability ratios [56], energy ratios [63] have been proposed to measure ductility because definition of ductility for steel reinforced concrete beam can not be directly applied to the FRPC strengthened RC beams. Experiments have indi￾cated catastrophic failure of strengthened beams due to low ductility. Spadea et al. [36] and Bencardino et al. [64] have suggested anchorage system to increase ductility, which is not affected by the change in the loading rate [42]. Grace et al. [65,66] performed experiments by using innovative triaxially braided ductile fabric which was reported to increase ductility. It was reported by Salom et al. [67] that torsional capacity of RC beams can be increased up to 70% with the help of FRPC strengthening. Ghobarah et al. [68] demonstrated experimentally that fully wrapped beams performed better than only strips and 45 orientation of fibers is more effective for upgrading torsional resistance. To avoid the extensive time consuming process by employing semi-skilled labour for application of FRPC to concrete surface, a commercial off-the-shelf-actu￾ated fastening system was used by Lamanna et al. [69] in experimental study by considering different fasters’ length and layouts. The technique was reported to be effective for bonding compared to conventional techniques. This method also increased ductility over the conventionally S.S. Pendhari et al. / Composite Structures 84 (2008) 114–124 115

16 S..Pendbari et al I Composte Siructures 84(2008)114-124 bonded method and took around 1/8 of time compared to 2.1.2.Shear behavior of RC beams strengthened by FRPC the conventiona members strer Shear strengthening of RC elements can be provided by d i epoxy y g ible bers par f th ever.there is a gap in knowledge on the effect of impact Various experimental and analytical works related to and fatigue loadings on the beam.Repeated loading can shear strengthening of beams with different FRPC lami- lead to internal cracks in a member which can alter its nates for l.acked racked beam 701 Erki and Meier Shahav antafillou).Deniaud and Cheng Lees et al.9 Masoud et al.[73].Heffernan and Erki [74].Brena et al. Pellegrino and Modena [98].Adhikary and Mutsuyoshi nted experim [99].Zhang and Hsu [10 It was observed ed fro n the e Fib ical of ndicular to the shear cracks.Shear contribution enhanced through the use of externally bonded CFRP argely dependent on the stress range pends on se paramete ding sur e prepar The perimental studies dise sed above have hee substantiated by analytical approach at macro level.In of main and shearnt shear span to efctive depth ratio. strength of FRPC. the simpli ana strain dept of sheet across beam te lo method or working method ns with about 19%in 79wherein issues related to rational design of external strenthened RC beams for interpreting major modes o The ultimate resistance of beam ca not be taken into ng next interfac separation flexura by simple superp of shear capacity cont Parametric study was performed by Picard et al.[80 which steel and FRPC.This has been reported to be the major obstacle in development of an analytica wh s An e I on amount of the mai ultimate loa 1 strengthene d beam usually starts crete and FRPC Malek and Saadatmanesh 04.105 degrade,as cracks are developed in concrete.Stiffness deg developed equilibrium and compatibility equations using considered ir Further,compres lin ic m re,contrar assumed to be linea r in elastic models Therefore it is nec as well as after formation of crack.Khalifa et al.106 the crack generation tion in 1edearhomshearcnehe8oandPRP gn algorit comput con tribution tio strengthened RC heams 107-109 have presented analvtical models to calculate the ultimate shear capacity of strengthened beams by assuming steel and concre lan nate inear elastic b chavior of FRP materials.R hond-sli non- gn n S can et a to evaluate delamination failure mode.On the other hand ever,numerical modeling of shear strengthened RC beams Colotti et al.[88]proposed a the retical model base with FRPC has not yet been addressed adequately in open and force transfer between concrete and 2 13 Durability of rc heams strengthened by frpc gate serviceability (cracking and deformability)criteria Seasonal and daily temperature variations cause freezing Yang et al. ractu based finit erential the expansion betwee method was obs cover separation failure mode in FRPC strengthened Cross-directional (matrix dominated)properties such as RC and tensio transverse tensile/c but iound to be hig

bonded method and took around 1/8 of time compared to the conventional method. The quasi-static behavior of flexural members strength￾ened with FRPC is well documented in literature. How￾ever, there is a gap in knowledge on the effect of impact and fatigue loadings on the beam. Repeated loading can lead to internal cracks in a member which can alter its stiff- ness and load carrying characteristics. Barnes and Mays [70], Erki and Meier [71], Shahawy and Beitelman [72], Masoud et al. [73], Heffernan and Erki [74], Brena et al. [75] and Bonfiglioli et al. [76] presented experimental results for static and fatigue failure of beams strengthened with CFRPC sheets. It is observed from the results that fatigue life of reinforced concrete beams could be significantly enhanced through the use of externally bonded CFRPC laminate and it is largely dependent on the stress range applied to steel reinforcement. The experimental studies discussed above have been substantiated by analytical approach at macro level. In all the simplified analytical models, strain compatibility has been used to predict flexural behavior either by ulti￾mate load method or working stress method [9,29,46,77– 79], wherein issues related to rational design of externally strengthened RC beams for interpreting major modes of failure including flexural, interface separation, flexural￾shear crack and concrete cover rip off have been addressed. Parametric study was performed by Picard et al. [80], which highlights the importance of concrete compressive strength whereas An et al. [81] emphasized on amount of the main reinforcement. Stiffness of concrete structures usually starts to degrade, as cracks are developed in concrete. Stiffness deg￾radation due to cracking of concrete is not considered in the simplified linear elastic models. Furthermore, contrary to actual behavior, stress–strain curve of concrete is assumed to be linear in elastic models. Therefore, it is nec￾essary to account for the crack generation and stiffness degradation in refined non-linear analysis. Studies in this direction were performed using finite element method to capture flexural behavior of strengthened RC beams [82–86] by assuming perfect bonding between concrete￾steel and concrete-FRPC laminate. Thomsen et al. [87], for example, developed non-linear finite element models using bond-slip relationship between concrete and FRPC to evaluate delamination failure mode. On the other hand, Colotti et al. [88] proposed a theoretical model based on truss-analogy. A non-linear analysis was performed by Aiello and Ombres [89] considering tension stiffening and force transfer between concrete and FRPC to investi￾gate serviceability (cracking and deformability) criteria. Yang et al. [90] presented fracture mechanics based finite element analysis to capture debonding failure. The method was observed to successfully simulate concrete cover separation failure mode in FRPC strengthened RC beams. Sato and Vecchio [91] developed a simple equation to estimate crack spacing, its width and tension stiffening effect. 2.1.2. Shear behavior of RC beams strengthened by FRPC Shear strengthening of RC elements can be provided by epoxy bonding of FRPC materials with fibers parallel, as practically possible, to the direction of the shear stresses. Various experimental and analytical works related to shear strengthening of beams with different FRPC lami￾nates for uncracked/cracked RC beams are reported by Sharif et al. [92], Chajes et al. [93], Chaallal et al. [94], Tri￾antafillou [95], Deniaud and Cheng [96], Lees et al. [97], Pellegrino and Modena [98], Adhikary and Mutsuyoshi [99], Zhang and Hsu [100]. It was observed that the shear strength of virgin beam can be increased by 60–120% using FRPC sheets. Fiber orientation may be vertical or perpendicular to the shear cracks. Shear contribution to the total shear capacity of strengthened RC beams depends on several parameter including surface prepara￾tion, composite fabric shear reinforcement ratio, amount of main and shear reinforcement, shear span to effective depth ratio, strength of FRPC, number of FRPC layers, wrapping schemes, depth of sheet across beam section [99,101–103]. U-wrap of sheet provided the most effective strengthening for RC beams with about 119% increase in shear strength. The ultimate resistance of beam can not be taken into account by simple superposition of shear capacity contri￾butions because of complex interaction between concrete, steel and FRPC. This has been reported to be the major obstacle in development of an analytical formula that can correctly predict the ultimate load of strengthened beams in shear [101,102]. By assuming a perfect bond between concrete and FRPC, Malek and Saadatmanesh [104,105] developed equilibrium and compatibility equations using truss analogy method. Further, compression field theory was used to calculate shear force resisted by FRPC plate, crack inclination angle, stresses in stirrups before cracking as well as after formation of crack. Khalifa et al. [106] reviewed research on shear strengthening and proposed a design algorithm to compute contribution of FRPC to shear capacity of RC beams. Another group of researchers [107–109] have presented analytical models to calculate the ultimate shear capacity of strengthened beams by assuming linear elastic behavior of FRPC materials. Review on dif￾ferent shear design methods can be found in Micelli et al. [110] with commentary on adequacy of each method. How￾ever, numerical modeling of shear strengthened RC beams with FRPC has not yet been addressed adequately in open literature. 2.1.3. Durability of RC beams strengthened by FRPC Seasonal and daily temperature variations cause freezing and thawing cycles, differential thermal expansion between concrete and FRPC substrate, resulting in premature plate separation and ultimately failure of strengthened system. Cross-directional (matrix dominated) properties such as transverse tensile/compressive strength and in-plane shear were found to be highly affected by environmental effects but fiber was less sensitive to it. 116 S.S. Pendhari et al. / Composite Structures 84 (2008) 114–124

S.S.Pendhari et al.Composite Stuctures 84(2008)114-124 avoided by using U-shape fabric s which provide ductility 111 of short-term environmental exposures on externally 2.2.Strengthening of RC cohmns using FRPC strengthened rc beams with FrPC by considering diffe ent wet/dry and freeze/thaw cycles Wrapping of FRPC sheets ar round conerete columns is a with concrete and reductio plication of fabr ng in strength is nearly 80-90%when strengthened system is othus technique isof practical in concrete co is he lac or latera ond failure prop ee of th of strengthened beams is very important and work in this ductility and energy absorption capacity of concrete speci nens by constructing ade tional R( 231 olumns or using grout-injected steel jack (0.in dki and Sherwood various conditions like drv 2.2.1.Axial behauior of rc columns strengthened with wet temperature,acids,alkali,etc.Creep and Shrinkage of FRPO ethods to en a udy lor and Wu 1471Bo along with different theoretical models and experimental et al.[148]Matthys et al.[149)Carey and Harries [150] Harajli [151]have investigated the axial behavior of con The co rete with rent FR Jackets from strength and ducti Grace and Singh [27)P ramid.bonded with en resins hav factors asso with vari ous ee successfully rehabilitation of rous paramete Effect of chloride nt and rehar corrosion wa ncrete stren studied by Wang et al.[12]whereas Maaddawy et al. t depth-to-width ratio53 551 longitudinal reinfor ment,stirrups. corrosion [129] developed teel,concrete dam e156 nber type rap angle [157] wrap [158 ratio [159. due effect on concrete-steeint direction [160] concrete dilation ratio [61 geometri and loading imperfection [162),etc.have been in 2.14.Bo and de gth of FRPO archer App rmed b substrate is a critical factor for effectiven ness of strengthen ing as delamination of FRPC laminate from concrete e su Shape of column section is a critical parameter affecting face can ure e structur Arduini an onfine of column I he mo enective conhn Buy 4etsobngh or circul 1311 1321 1331 Nguyen et al.34)Sebastian [135]and Lore sections engage high confining pre ure at their co [136]perfor perimenta addres ure on their flat side herefor on is ne th r ested use of rubber toughened ep Bond confinement for rectangular and square columns.the col between FRPC and concrete surface also depends on prep amn section can be modified into the elliptical section.that aration of concrete surface (water or sand blasting he corne have to be rounded toprevent prematur and sh of 1641 etc.Considerable research was performed by usin ancho strengthened with CFRPC was studied by Ye et al.[167 bolts or U-shape er fabrics at the end [32,132.138,139]t ho concluded that shear strength of R( column can be odpnat nfined b crete gets disturbed because of anchor bolt.This can be ERPC was investigated by many researchers [1681761

Karbhari and Engineer [111], Karbhari and Zhao [112], Sen et al. [113], Sen et al. [114,115], Green et al. [116], Aiello et al. [117], Bisby and Green [118], examined effect of short-term environmental exposures on externally strengthened RC beams with FRPC by considering differ￾ent types of fibers, different wet/dry and freeze/thaw cycles, etc. It was observed that degradation occurs primarily at the level of resin in contact with concrete and reduction in strength is nearly 80–90% when strengthened system is subjected to high temperature range [119]. A simple analyt￾ical model is proposed by Bisby and Green [118] to predict bond failure because of thermal load. Long-term behavior of strengthened beams is very important and work in this direction was reported by Karbhari and Engineer [111], Plevris and Triantafillou [120], Xie et al. [121], Karbhari and Shulley [122], Saadatmanesh and Tannous [123], Sou￾dki and Sherwood [124] under various conditions like dry/ wet temperature, acids, alkali, etc. Creep and Shrinkage of strengthened beam was studied by Plevris and Triantafillou [120] and Bank et al. [125] who presented different test methods to study long-term behavior of FRPC structures along with different theoretical models and experimental techniques to predict effects of different environmental con￾ditions. The combined effect of harsh environment and fati￾gue loading was studied by Gheorghiu et al. [126] on flexural behavior. Recently, Grace and Singh [127] pro￾posed strength reduction factors associated with various independent environmental conditions like 100% humidity, salt water, alkali solution, freez-thaw, thermal expansion, etc. Effect of chloride content and rebar corrosion was studied by Wang et al. [128] whereas Maaddawy et al. [129] developed mathematical model for prediction of inelastic response of strengthened RC beams by taking into account reduction of steel area due to corrosion and its effect on concrete-steel interface. 2.1.4. Bond and development length of FRPC Bond of external FRPC reinforcement to the concrete substrate is a critical factor for effectiveness of strengthen￾ing as delamination of FRPC laminate from concrete sur￾face can cause failure of concrete structure. Arduini and Nanni [33], Arduini et al. [130], Buyukozturk and Hearing [131], Swamy and Mukhopadhyaya [132], Nakaba et al. [133], Nguyen et al. [134], Sebastian [135] and Lorenzis et al. [136] performed experimental studies to address bonding issue of FRPC plates. Experiments with different epoxies were also conducted by Saadatmanesh and Ehsani [26] who suggested use of rubber toughened epoxies. Bond between FRPC and concrete surface also depends on prep￾aration of concrete surface (water jet or sand blasting), concrete compressive strength and effective bond length [137], fibers stiffness and shape of stress distribution [134], etc. Considerable research was performed by using anchor bolts or U-shape fiber fabrics at the end [32,132,138,139] to avoid premature failure of FRPC plates from concrete sur￾face. This technique increases ductility but original con￾crete gets disturbed because of anchor bolt. This can be avoided by using U-shape fabrics which provide ductility as well as increased shear strength. 2.2. Strengthening of RC columns using FRPC Wrapping of FRPC sheets around concrete columns is a promising method for structural strengthening and repair. Application of fabric sheet is quite easy, requiring no spe￾cialized tools; thus technique is of practical interest. One of the deficiencies in concrete columns is the lack of lateral confinement and low energy absorption capacity. External confinement of concrete significantly enhances strength, ductility and energy absorption capacity of concrete speci￾mens by constructing additional RC cage around existing columns or using grout-injected steel jackets [140,141]. 2.2.1. Axial behavior of RC columns strengthened with FRPC A number of studies including Demers et al. [142], Nanni et al. [143], Saadatmanesh et al. [144], Seible et al. [145], Hanna and Jones [146], Xiao and Wu [147], Bousias et al. [148], Matthys et al. [149], Carey and Harries [150], Harajli [151] have investigated the axial behavior of con￾crete with different FRPC jackets from strength and ductil￾ity point of view. FRPC wraps consisting of carbon, aramid and glass fibers, bonded with epoxy resins have been successfully applied for seismic rehabilitation of bridge piers in USA and Japan [152]. Various parameters affecting the performance of confined columns’ systems including concrete strength, depth-to-width ratio [153– 155], longitudinal reinforcement, stirrups, corrosion of steel, concrete damage [156], fiber type, wrap angle [157], thickness of wrap [158], slenderness ratio [159], deformabi￾lity of the concrete, stiffness of the jacket in the lateral direction [160], concrete dilation ratio [161], geometric and loading imperfection [162], etc. have been investigated by researchers. Application of pretensioned FRPC sheet for strengthening of RC columns has been performed by Mortazavi et al. [163]. Shape of column section is a critical parameter affecting confined strength of column. The most effective confine￾ment is obtained for circular columns rather than rectangu￾lar and square columns [164–166]. Square or rectangular sections engage high confining pressure at their corners but little pressure on their flat sides, therefore the cross-sec￾tion is not effectively confined, resulting in a lower increase in strength [142]. In order to increase the effectiveness of confinement for rectangular and square columns, the col￾umn section can be modified into the elliptical section, that is, the corners have to be rounded to prevent premature failure but radius is limited because of internal longitudinal reinforcement [164]. Shear strength of RC columns strengthened with CFRPC was studied by Ye et al. [167] who concluded that shear strength of RC column can be effectively increased with external strengthening. Structural behavior of concrete columns confined by FRPC was investigated by many researchers [168–176] S.S. Pendhari et al. / Composite Structures 84 (2008) 114–124 117

8 S.S.et al IComposite Structures 84(2008)114-124 using analytical models to predict stress-strain behavio 2.2.3.Durability of RC columns strengthened by FRPC be are Landg nd th ing mater et al.[1401.for example.developed an analytical model and concrete Exposure of various environmental condi e e tions usually resulted in decrease of strength.stiffess and pos ility of cl 95].Tou This failure mode Ten [701]Tat [177]to analyze behavior of that exposure to wet-dry environments has little effect on of various cross-sections strength and CFRP wrapped specime hH et al.[140]by considering st rain energy approach.A design GFRPC wrapped specimens are equally susceptible to procedure was proposed by Theria lt and Neale [179]to searchers [198 improve axia ngular co stu on stren ning o sented a st of fibers and concluded nearly 20 increase in load carr and lateral direction for axially loaded rectangular short with FRP am and eng h strengthened ause orcement due to dir ction only which can he dire tly use T model is applicable for concrete confined by all types of FRPC as well as steel.Recently,comparisons of various 2.3.Strengthening of RC beam-columns ioint by FRPC presented by n ioints is ve nt ir 222.Seismie behavior of RC colmns strengthened by s.Shear failure of bea colun al cau large lateral cyelic ng recent earthaua in premature failure of column.Retrofitting of columr have been attributed to inadequate transverse reinforce- recent anc ments at the joint and weak- u and one ted Rnee thady on ex umns improves significar ntly because of confining the columns is high and beam reinforcement is less than wraps [183-185]The .2 Several te chniques have been applied to strengthen ing use th E of deterioration under larg eversal cyelic loading thar effective confinement in the rehabilitation of beam-column the virgin columns [186].Amount of external reinforce ioints.Use of FRPC for strengthening of dilapidated rein orced concrete structures has increased recent years Xiao and Ma [187 develo b considering the bond-slip deterioration of lap spliced lon- forcement is an effective method to increase moment car gitudinal bars for seismic ent and retrofit design capacity o under combined axial and cyclic lateral loading.Finite Various researchers have conducted exneriments on element analysis results indicated that FRPC fabric strengthening of beam-column joints from a ductility point showed strength well a ol view to u lerstand failure mo e with and without a cho at the age using with ellective for strengthening in t joint region.Pulid et a annag and 21]perfor

using analytical models to predict stress–strain behavior between confined concrete and FRPC wraps. Analytical models are based on deformation compatibility and equi￾librium of forces between concrete and FRPC. Mander et al. [140], for example, developed an analytical model to calculate increased compressive strength of concrete in RC column due to confining pressure provided by trans￾verse reinforcement. This model was further modified by Teng and Lam [166], Wang and Restrepo [170], Tan [171], Saadatmanesh et al. [177] to analyze behavior of RC columns wrapped with FRPC of various cross-sections like circular, elliptical, square and rectangular. Mirmiran and Shahawy [178] modified model suggested by Mander et al. [140] by considering strain energy approach. A design procedure was proposed by Theriault and Neale [179] to improve axial load capacity of circular and rectangular col￾umns confined with FRPC wraps. Chaallal et al. [180] pre￾sented a stress–strain curve by considering fibers in axial and lateral direction for axially loaded rectangular short columns confined with FRPC jackets. Lam and Teng [181] developed a stress–strain curve with fibers in hoop direction only, which can be directly used in design. This model is applicable for concrete confined by all types of FRPC as well as steel. Recently, comparisons of various available confinement models have been presented by Bisby et al. [182]. 2.2.2. Seismic behavior of RC columns strengthened by FRPC A large lateral cyclic earthquake force can degrade strength of concrete and reinforcing bar that can result in premature failure of column. Retrofitting of column components to withstand earthquakes is a recent and widespread task and one of the more complex engineer￾ing challenges. Seismic resistance of retrofitted RC col￾umns improves significantly because of confining action of the FRPC wraps [183–185]. The technique has been observed to improve displacement ductility as well as strength. Further, repaired specimens exhibit lower rate of deterioration under large reversal cyclic loading than the virgin columns [186]. Amount of external reinforce￾ment required depends on level of axial load and extent of damage. Xiao and Ma [187] developed an analytical model by considering the bond-slip deterioration of lap spliced lon￾gitudinal bars for seismic assessment and retrofit design. A non-linear finite element analysis was performed by Parvin and Wang [188] on FRPC jacketed RC column under combined axial and cyclic lateral loading. Finite element analysis results indicated that FRPC fabric showed significant improvement in strength as well as ductility in potential plastic hinge location at the bottom of column. Elsanadedy and Haroun [189] proposed seis￾mic design procedure for circular lap-splice reinforced RC column upgraded with FRPC jackets based on moment curvature analysis with inclusion of bond-slip mechanism. 2.2.3. Durability of RC columns strengthened by FRPC Environmental exposures to conditions such as freeze￾thaw can potentially affect confining material (FRPC) as well as confined concrete and the bond between composite and concrete. Exposure of various environmental condi￾tions usually resulted in decrease of strength, stiffness, and possibility of change in failure mode [190–195]. Tout￾anji and Balaguru [196,197] reported that CFRPC is supe￾rior to GFRPC under harsh environment. It was observed that exposure to wet–dry environments has little effect on strength and ductility of CFRPC wrapped specimens. On the other hand, GFRPC wrapped specimens exhibited about 10% reductions in strength. However, CFRPC and GFRPC wrapped specimens are equally susceptible to freeze-thaw cycles. Another group of researchers [198– 200] performed experimental studies on strengthening of corrosion damaged RC columns by using different types of fibers and concluded nearly 20% increase in load carry￾ing capacity with 50% decrease in rate of post repair corro￾sion but the strengthened system exhibited somewhat reduced ductility because of loss of reinforcement due to corrosion process. 2.3. Strengthening of RC beam-columns joint by FRPC Performance of beam-column joints is very important in determination of the ability of structure to withstand large earthquake and other lateral loads. Shear failure of beam￾column joints has been identified to be the principal cause for collapse of many moment resisting frame buildings dur￾ing recent earthquakes. Shear failure during an earthquake have been attributed to inadequate transverse reinforce￾ments at the joint and weak-columns/strong-beam design. A study on external beam-column joint has shown failure of the structure by beam hinging [201] if axial load on the columns is high and beam reinforcement is less than 1.2%. Several techniques have been applied to strengthen beam-column joints, including uses of concrete jackets, bolted steel plates [202]. However, it is difficult to provide effective confinement in the rehabilitation of beam-column joints. Use of FRPC for strengthening of dilapidated rein￾forced concrete structures has increased in recent years. However, behavior of beam-column connection is complex and still not completely understood. External FRPC rein￾forcement is an effective method to increase moment carry￾ing capacity of beam-column connection by about 60% [203] and shear capacity of the joint by about 35% [204,205]. Various researchers have conducted experiments on strengthening of beam-column joints from a ductility point of view to understand failure mode with and without anchor￾age using different types of FRPC with variable angle of fibers and numbers of layers [205–210]. It has been observed that fibers inclined at 45 to the direction of principal planes are most effective for strengthening in the joint region. Pulido et al. [211], Shannag and Alhassan [212] performed experi￾mental studies on seismic behavior of beam-column joints. 118 S.S. Pendhari et al. / Composite Structures 84 (2008) 114–124