Shaking Table Tests of a Reinforced Concrete Frame Subjected to Mainshock-Aftershock Sequences

This paper presents the shaking table tests for a 1/5-scale 5-story reinforced concrete (RC) frame subjected to mainshock (MS)-aftershock (AS) sequences for investigating the unfavorable effects of ASs on structural performance. The prototype of the test specimen, which was heavily damaged in M-w 7.9 Wenchuan earthquake, was a teaching building designed and built according to the old version of Chinese design codes. The ground motion records of one MS and three ASs were selected from the Wenchuan strong ground motion database to compose the seismic sequence. A series of peak ground acceleration (PGA) intensity levels were considered to scale the seismic sequence entirely for the simulation of sequential excitations. During the tests, typical global and local damage phenomena of the specimen were observed. Structural responses and dynamic properties of the specimen were monitored and calculated. An Aftershock Influence Ratio (AIR) defined as the ratio between the structural response due to an AS and that due to the corresponding MS was proposed to quantify the effects of ASs. Results show that AIR values are increased significantly as the growth of the accumulative damage of the specimen. Amongst the investigated structural response parameters, the absolute acceleration is impacted mostly by ASs with the corresponding AIR value as large as 85.2%, while the relative displacement is impacted least since the corresponding maximum AIR is only 27.9%. Moreover, at a given accumulative damage level of the specimen, the second AS (AS-II) has the largest effect on structural performance compared to others. This experimental investigation highlights the complex AS effects on structural performance since they are closely correlated to the accumulative damage of the structure mainly caused by MS, structural response parameters, and AS characteristics. It is thus necessary to well consider the AS effects in seismic performance evaluation and seismic design of the structures especially located in the sites with high seismicity.