Shake Table Tests of Large-Scale Substandard RC Frames Retrofitted with CFRP Wraps before Earthquakes

Abstract

A large number of substandard reinforced concrete (RC) frames exist in potential earthquake regions across the world. These frames are at high risk of collapse during possible strong earthquakes in the future. In order to mitigate the risk, pre-earthquake seismic strengthening of these frames is urgently needed. This paper presents an experimental study on the seismic performance of substandard RC frames strengthened with externally bonded carbon-fiber-reinforced polymers (CFRP) composites using shake table tests. Two 1/2-scale 4-story and 2-bay RC frames were fabricated and tested on a shake table. One specimen was tested first as the control specimen, while the other specimen was retrofitted with CFRP before test. The retrofitting scheme was designed according to the failure mode of the control specimen, and involved CFRP wrapping at and close to the beam-column joints at the lower two stories of the frame. The test results showed that the seismic performance of the substandard RC frame could be significantly improved by the CFRP strengthening technique. The maximum applied peak ground acceleration (PGA) that could be resisted by the control frame specimen was approximately 0.6g, while the retrofitted frame specimen could endure seismic loading with a PGA value of 1.0g without significant damage. The horizontal displacements, interstory drift ratios, and torsional displacements of the retrofitted frame specimens were also found to be much smaller than those of the control frame at the same earthquake levels.