Seismic fragility of steel special truss moment frames with multiple ductile vierendeel panels

Special truss moment frames (STMFs) are used as the lateral force-resisting systems in buildings. Under seismic loading, the hysteretic energy dissipation in STMFs mostly occurs through the flexural plastic hinges developed in the special segments only. This study presents the seismic fragility assessment of low to high-rise STMFs with ductile Vierendeel panels as the special segments. Four building frames (i.e., 3-, 6-, 9-, and 15-story) with three different configurations of special segments in STMFs have been considered as the study frames. Nonlinear incremental dynamic analyses of the study frames have been carried out using computer software PERFORM-3D using forty-four ground motion records. The probability of exceeding the drift levels corresponding to three performance levels, viz., immediate occupancy (IO), life safety (LS), and collapse prevention (CP) of the study frames have been investigated under the design-basis earthquake and maximum considered earthquake hazard levels. The presence of intermediate vertical members in the Vierendeel panels resulted in the gradual loss in the post-peak lateral strengths of STMFs. The use of multiple Vierendeel panels significantly reduced the probability of failure of low-rise (namely, 3-and 6-story) STMFs. However, STMFs with single Vierendeel panels are found to be beneficial in 9-and 15-story building frames. The inter-story drift limits have been proposed for the performance levels of IO, LS, and CP of STMFs.