Performance evaluation of buckling-restrained braced frames under repeated earthquakes

Structures in earthquake-prone areas are not subjected to a single seismic event, but also to a seismic sequence consisting of mainshock and several aftershocks. However, the influence of seismic sequence on performance of structures has not been addressed in majority of existing seismic codes. This paper investigates the effect of repeated earthquakes on performance of steel buckling restrained braced frames. For this purpose, 4-story and 10-story prototype buckling restrained braced frames, designed according to Iranian building codes, are exposed to five seismic sequences. Nonlinear time history analyses are conducted and the responses of frames are measured in terms of maximum inter-story and residual drifts. Furthermore, Park-Ang damage indices and global ductility factors are obtained for braced frames under examined mainshocks and mainshock-aftershock sequences. From the results of this research, it is found that the seismic sequence has the potential to increase the inter-story drift, residual drift, damage index and global ductility factor of buckling restrained braced frames. It is also highlighted that the spectral acceleration of mainshock-aftershock sequence, in comparison to that of single event mainshock, considerably affects the performance of buckling restrained braced frame under repeated earthquakes.