Seismic collapse assessment of intermediate RC moment frames subjected to mainshock-aftershock sequences

Abstract

This paper assessed the effects of mainshock-aftershock (MS-AS) sequences on the seismic vulnerability of intermediate reinforced concrete moment frames (IRCFs), considering various mainshock intensity scenarios. Moreover, given the limited library of real MS-AS ground motion sequences in the Iran plateau, a MS-AS sequence-selection method is proposed to generate artificial sequences that incorporate the magnitude, seismotectonic region, fault mechanism, and site condition of a target area. Three 4-, 7-, and 10-story IRCFs, modeled in OpenSees software, are subjected to real as well as artificial MS-AS sequences and collapse fragility curves are derived using the incremental dynamic analysis (IDA) results. The results show that the occurrence of mainshock can significantly increase the vulnerability of buildings during the aftershock. For various mainshock intensity scenarios, a general decrease in the collapse capacity is observed across all mainshock-damaged buildings, with a more significant decrease for taller buildings. Hence, it is essential to consider the effects of aftershock in the seismic design of IRCFs to mitigate the risk of collapse. Furthermore, by comparing the seismic responses caused by artificial sequences with those caused by real sequences, the validity of artificial sequence-selection method is confirmed; thus, artificial sequences can be used as a substitute for real sequences. Regression equations are also presented to predict the collapse capacity reduction of frames with different story numbers in presence of various mainshock intensity scenarios.

Keywords

• Mainshock-aftershock sequence
• Fragility curve
• Incremental dynamic analysis (IDA)
• RC moment frame
• Seismic collapse capacity