Attempt for seismic retrofit of existing substandard RC members under reversed cyclic flexural effects

Many existing reinforced concrete (RC) substandard structures in seismically active regions, designed and/or constructed improperly or constructed before up-to-date seismic design codes, are in urgent need of seismic retrofitting. Beside financial issues, disturbance to the occupants and functions of the structures are among obstacles for seismic retrofitting. Utilization of fiber reinforced polymer (FRP) composites can reduce disturbance to the occupants and hindrance of the functions of the structures remarkably. In this study, the applicability of flexural seismic retrofitting using carbon FRP precured laminates and rods is investigated experimentally. In seismic retrofitting, the key issue is the effect of reversed cyclic actions, which impose cycles of compression and tension stresses on the FRP reinforcement. Two major issues examined in the study are (1)the anchorage of FRP precured laminates/rods used for cyclic flexural strengthening to the low-strength concrete support (foundation) and (2)the efficiency of the presented flexural seismic retrofit technique for the case of low-strength concrete members subjected to reversed cyclic loading conditions. Furthermore, the flexural strengths of the reference and retrofitted specimens are predicted analitically. The accuracy of the predictions varied depending on the assumed and actual failure modes of the specimens.