Impact of ground motion duration on seismic performance of buckling restrained braced frames

Buckling restrained braced frames (BRBFs) are commonly employed as seismic lateral force resisting system due to their high stiffness and energy dissipation capacity. However, under long-duration strong earthquakes, buckling-constrained braces are susceptible to fracture due to low-cycle fatigue. Previous studies evaluating their seismic performance have not considered the impact of earthquake duration on the results. This study evaluates the impact of ground motion duration on the seismic performance of BRBFs. By employing 44 pairs of spectrally equivalent ground motions with varying durations, the impact of ground motion duration is studied independently from other effects arising from ground motion amplitude and acceleration spectral shape. Nonlinear numerical models considering low-cycle fracture of buckling restrained braces are developed for 4-, 8-, and 12-story archetypes. The effects of ground motion duration on the seismic performance of BRBFs are examined using standard performance and collapse-assessment procedures. The results indicate that under seismic excitations not exceeding the maximum considered earthquake level, ground motion duration does not significantly affect the structural maximum interstory drift, but longer duration generally results in larger cumulative plastic deformation for the buckling restrained brace. Meanwhile, ground motion duration has a significant impact on the results of collapse risk evaluation. In addition, using combined duration- and spectrum-related intensity measure can better evaluate the damage potential of ground motion.