The role of overstrength on the seismic performance of asymmetric‐plan structures

Abstract

SummaryUneven distribution of seismic demand in asymmetric‐plan structures is a critical concern in earthquake‐resistant design. Contemporary seismic design strategies that are based on linear elastic response, single load reduction factor, and uniform ductility demand throughout an asymmetric system generally lead to unsatisfactory performance in terms of realized ductilities and nonuniform damage distribution due to strong torsional coupling associated with asymmetric‐plan systems. In many cases, actual nonlinear behavior of the structure displays significant deviation from what is estimated by a linear elastic, force‐based seismic design approach. This study investigates the prediction of seismic demand distribution among structural members of a single‐story, torsionally stiff asymmetric‐plan system. The focus is on the effect of inherent unbalanced overstrength, resulting from current force‐based design practices, on the seismic response of code‐designed single‐story asymmetric structures. The results obtained are utilized to compile unsymmetrical response spectra and uniform ductility spectra, which are proposed as assessment and preliminary design tools for estimating the seismic performance of multistory asymmetric structures. A simple design strategy is further suggested for improving the inelastic torsional performance of asymmetric systems. Providing additional strength to stiff edge members over their nominal design strength demands leads to a more balanced ductility distribution. Finally, seismic responses of several asymmetric case study structures designed with the aid of the proposed strategy are assessed for validating their improved performance.