Evaluation of Torsional Parameters in Seismic Code Provisions for Multi-story Unsymmetric-Plan Buildings

Abstract

AbstractSeismic code provisions define torsional parameters to evaluate in-plan irregularity levels for the design of complex structures. These parameters are important to determine the structural analysis method for their seismic assessment and design. For irregular structures, seismic codes introduce special provisions and restrictions, while for symmetric plan structures, traditional linear design procedures are adequate. The ASCE/SEI 7–16 and the ASCE 41–17 require that the maximum story drift, from a linear response spectrum analysis, to be less than 1.2 times the average story drift at the two ends of the structure to avoid torsional irregularities. Although the ASCE 7–16 requirement is simple to define in-plan irregularity levels, it ignores the variation of stiffness and the redistribution of torsional loads when structures are subjected to high levels of seismic inelastic demands. To evaluate these shortcomings, this paper presents results from a nonlinear three-dimensional model of an unsymmetric-plan multi-story building subjected to two horizontal components of ground shaking considering different levels of seismic excitation for a suite of thirty ground motion records. Results from non-linear response history analyses (RHAs) show that the ASCE 7–16 torsional parameters might be adequate to define in-plan irregularity, with low record-to-record variability and consistency for different levels of seismic excitation.