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