Expected seismic fragility of code-conforming RC moment resisting frames under twin seismic events. (March 2020)

• Record Type: Journal Article
• Authors: Kalantari, A.; Roohbakhsh, H.
• Is Part Of: Journal of building engineering. Volume 28(2020)
• Publication Date: 2020-03
• Subjects: Seismic sequence -- Nonlinear dynamic analysis -- RC buildings -- Seismic performance -- Fragility curve; Building -- Periodicals; 690.05
• DOI: 10.1016/j.jobe.2019.101098
• Languages: English
• ISSNs: 2352-7102

Abstract

Abstract: Seismic design codes require buildings to be designed only for one seismic event, neglecting the possibility of multiple earthquake events. However considerable damage and loss is observed due to aftershocks where buildings have been affected by the first event. The purpose of this research is to introduce fragility curves of code-conforming reinforced concrete moment resisting frames (RCMRFs) under aftershock. Three RC moment resisting frames of 4, 8 and 15 stories, are loaded and designed based on the latest three editions of the Iranian code of seismic design for buildings referred to as Standard No. 2800 (STD-2800). The nine designed frames are then numerically simulated in OpenSees software to perform nonlinear dynamic analysis. Twenty natural ground motion sequences, each including two seismic events, were selected from previous studies for the purpose of nonlinear incremental dynamic analysis. Maximum inter-story drift was employed as a damage index, to capture performance of the RC frames under the sequences. The accepted performance for the collapse level was taken from Iranian instructions for seismic rehabilitation of existing buildings, PBO-Publication No. 360, 2007, which is similar to ASCE 41-13. Seismic fragility values are calculated for the buildings in the second event after being damaged in different first event intensity scenarios. Assuming a log-normal distribution for the failure probability function, corresponding values of mean, μ, and standard deviation, β, for each case are calculated and discussed. Results indicate how the probability of failure in the seismic fragility curves may differ as a result of the effects of a first event scenario. It is also shown how updating the design criteria as well as the height of frames can affect fragility in a second event. Highlights: Significant increae of probability of failure under an mainshock-aftershock sequence was observed for mainshocks with larger PGA intensity. IDA results of the aftershock records for RC frame affected by different scenarios of mainshock PGA intensities were presnted. The trend of enhancement of performance of RC moment frames design based on different editions of STD-2800 under different mainshock-sftershock seuence scenarios was calculated and presented.