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