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]perforusing 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