Seismic performance of multi-storey steel frames with semi-rigid joints

In this paper, a numerical study on the response of multi-storey moment-resisting steel frames subjected to seismic actions, accounting for the real behavior of both the beam-to-column joints and the column bases, is presented. Two real benchmark buildings are considered for the purpose. The examined buildings are characterized by beam-to-column joints and column bases with semi-rigid and partial-strength behavior, although they were improperly assumed as rigid and full-strength in the original design process of the frames. In order to appraise how this wrong assumption influenced the building safety, finite element models are set up, first by modelling the joints according to the original design approach and then including the real stiffness and strength. Nonlinear dynamic analyses are performed and fragility curves for different limit states are obtained, considering the record-to-record variability as main source of uncertainty.