Aftershock collapse capacity assessment of special steel moment frame structures

Abstract

This study assessment of the collapse capacity of special steel moment frames (SSMFs) with considering earthquake shock sequences for structures height from 4 to 20 stories. The collapse capacity is expressed in terms of the Sa(T1) value at which the system reaches the collapse state. Collapse identification relies on the capability of the model to accurately simulate damage of members and the resulting behavior deterioration. The softening in the lateral response expressed in terms of maximum interstory drift (MID) when it is expressed against the Sa(T1) values is thus used to identify collapse occurrence. The mainshock-aftershock (MS-AS) effect and the uncertainties associated with it are simulated by utilizing a set of 32 natural record pairs. The level of damage induced by MS is represented by two parameters including MID and peak residual story drift (PRSD). Using these parameters, the MS is applied so as to various pre-selected damage levels are imposed. For each MS damage level, an incremental dynamic analysis (IDA) is performed using the AS record that follows MS and a free vibration phase. The AS intensity causing the collapse state is finally identified and respected for evaluating the effect of MS damage level. The correlation between the median collapse Sa's, called aftershock median collapse capacity, and the MS damage indicated by MID and PRSD parameters is quantified. The study results indicate that larger mainshock damages are required to reduce the collapse capacity of high-rise SSMFs compared to low- to mid-rise structures. Furthermore, the structural collapse capacity may reduce significantly when the building is subjected to a high intensity MS. A comparison between the trendlines presented by the regression equations developed in terms of the MID and PRSD variables was indicated that the MID parameter was more predictable trend.The PRSD parameter was, however, said to be useful in the sense that its value could be measured just after an MS excitation.