A New Method for Seismic Collapse Assessment of Mid-Rise Concrete Buildings

Collapse is the most critical performance level of seismic assessment of concrete buildings. Most of the conventional collapse assessment methods employ incremental dynamic analysis (IDA) for an equivalent single degree of freedom system. Meanwhile, the ambiguity about the stories, where the maximum engineering demands (such as drifts) occur, has raised grave doubts about the efficiency of the IDA for the conventional collapse assessment approach. This study proposes a new method to overcome this shortcoming by improving the existing IDA-based technique. For this purpose, a matrix is made up of drifts resulted from a pushover analysis of a multi-degree of freedom frame. This matrix of critical drifts is employed in the interpretation of the IDA results. Therefore, those stories, that experience partial collapse, are identified. To illustrate how the proposed methodology is implemented, two sets of 7- and 10-story typical building frames are modeled. It is assumed that they would fail in the flexural mode, and also the premature failure of the joints would never occur under seismic excitations. This new methodology results in a more conservative assessment of the collapse capacity in comparison with the IDA-based conventional method. Therefore, the proposed method is reliable enough to predict the building collapse possibility. In this method, the uncertainty associated with the estimated collapse limit state is lower than the conventional approach evaluation.