Parametric study on the collapse probability of modern reinforced concrete frames with infills

Abstract

This study aims to compare the collapse probability of reinforced concrete infilled frames designed in accordance with modern Indian seismic codes. Multiple versions of bare and infilled (both fully and partially) frames are considered. A total of 33 frames are divided into eight sets based on the parameter being varied, namely, the quality and thickness of infills, design code, aspect ratio, and number of stories. The collapse probability is evaluated through multiple stripe analysis with eight stripes corresponding to different return periods. A set of 40 ground motions, consistent with the site-specific uniform hazard spectra corresponding to each return period, is selected. Results suggest that the frames designed for pre-2016 Indian codes perform considerably worse than those designed for post-2016 Indian codes, which are on par with other national codes. The effect of collapse probability of addition of infills to bare frames is found to be negligible to significantly negative depending on factors such as adopted design code, relative strength of infill strut to columns, aspect ratio, and number of stories. Four-story frames perform worse than 8-story frames. Interestingly, the 8-story open first story frames, designed for modern codes, are not found to be significantly more vulnerable than their fully infilled counterparts.