Analytical assessment of CFRP retrofitted reinforced-concrete buildings subjected to near-fault ground motions

Application of externally bonded fiber-reinforced polymers (FRPs) in the form of composite sheets has received a great deal of attention in the last two decades. However, their efficiency in improving the seismic performance of reinforced concrete (RC) structures subjected to near-fault ground motions has not yet been scrutinized in detail. Seismic motions near the fault rupture can be characterized by a large long-period velocity pulse at the beginning of the earthquake, causing severe damage or even collapse of code-compliant buildings. Although seismic design codes cannot adequately address the effect of these impulsive ground motions on structures, retrofitting of many important buildings located in regions near the active faults is high priority. Towards this, a numerical investigation is conducted in this study on the seismic retrofitting of existing RC building structures under near-fault ground motions using carbon FRP (CFRP) sheets. As the case study, an 8-story RC moment resisting frame was selected to represent the midrise buildings. Aimed at improving the lateral strength of the structure, CFRP retrofits were applied to the top and bottom (flange) sides of the beams and columns in the regions prone to inelastic behavior during the strong ground motion. Seismic responses of the original and retrofitted structures were evaluated using nonlinear time-history analysis performed under a set of near-fault ground motions possessing directivity pulses. The results were compared in terms of distribution of maximum interstory drifts and plastic deformations at beams and columns. It was shown that the adopted retrofitting scheme can substantially improve the seismic behavior of existing code-compliant RC structures subjected to impulsive seismic motions