Probabilistic seismic demand assessment of special truss moment frames with Vierendeel panels under geometric variations

Special truss moment frames (STMFs) have attracted growing interest due to the demand for column spacing that exceeds conventional restrictions. This study investigates the seismic performance of 27 three-span STMFs with mid-span Vierendeel truss panels having different structural configurations. The considered STMFs include three, six, and nine stories; span lengths of 10, 15, and 20 m; and have special ductile segment lengths of 1, 1.5, and 2.25 m. Incremental dynamic analyses (IDA) of STMFs were performed under 22 strong ground motions to assess the dependence of structural responses on geometric configurations while explicitly accounting for record-to-record uncertainty. Seismic demand models and fragility curves were constructed using Bayesian statistics and combined with site-specific hazard curves in a probabilistic seismic demand analysis (PSDA). The results indicate that the structural seismic performance of STMFs is strongly affected by the height-to-span (h/L) and the special segment length-to-span (Lₛ/L) ratios. Seismic demand predictive equations in terms of geometric parameters were proposed and validated against numerical data, confirming their reliability for preliminary seismic assessment. The results demonstrate that, within the studied range of parameters, reducing either the height-to-span ratio (h/L) or normalized special segment length (Lₛ/L) leads to improved seismic performance of STMFs.