Performance Evaluation and Damage Detection of FRP-retrofitted RC Frames

Performance based assessment (PBA) can be used for damage detection of FRP-retrofitted RC moment resisting frames. PBA can be evaluated using nonlinear pushover analysis according to current codes. In this paper, performance of an existing RC frame that has been retrofitted with steel-braced by other researchers is assessed in order to evaluate the ability of the FRP-web bonded system to upgrade the performance level and ductility of the frame. For this purpose, the base shear-roof displacement (capacity curve) of the plain and retrofitted frames obtained from the pushover analysis has drawn into the spectral acceleration and spectral displacement curves from the Iranian Code for Earthquake Design of Building (2800). The flexural stiffness of FRP-retrofitted exterior and interior joints of each level of the RC frame is determined using nonlinear finite element (FE) analysis. The obtained stiffness is implemented in a mathematical model of frame in order to simulate the web-bonded FRP system and then pushover analysis is performed. Finally, the seismic performances of the retrofitted frames are compared with the similar plain frame. Based on the capacity curve, a global damage index, which represents the integrated performance of frames at the performance point (and at the life safety) is presented and discussed. The evaluation demonstrated that the damage index of the frames is reduced after retrofitting, particularly by FRPs and that the FRP-retrofitted frame has a lower damage index at life safety (LS) compared with steel braced frames. This study shows that the proposed method is suitable for structural damage detection of retrofitted RC buildings using capacity curves.