Effective Assessment of Inelastic Torsional Deformation of Plan-Asymmetric Shear Wall Systems

Abstract

Torsional deformation may occur in plan-asymmetric wall structures during seismic events. In most current seismic design codes, the torsional deformation is handled using the concept of design eccentricity, in which design loads may be excessively amplified. This approach has limitations in accurately estimating the torsional deformation of the plan-asymmetric structures, mainly because it is based on linear elastic material behavior. In this paper, we propose a simple method that can accurately evaluate the inelastic lateral displacement and rotation of plan-asymmetric wall structures and is suitable for use in the displacement-based design method. The effectiveness of the proposed method is verified by comparing its predictions with the results of rigorous time history analyses for a model problem. The comparison shows that the proposed method is able to provide accurate estimates of the inelastic torsional deformation for the plan-asymmetric wall system, while requiring less computational cost than the time history analysis. become quite different from those in the elastic range. Some of the current design code provisions provide a simple solution to this problem by introducing the so-called accidental eccentricity, which is equivalent to the elastic eccentricity amplified by a certain factor. However, this accidental eccentricity may require excessive strength and stiffness for lateral force resisting components since it does not properly consider the actual torsional failure mechanism of the structure.There has been a lot of research performed to remove the limitations of the current seismic design codes and develop a proper design process. Early stage research on this issue focused on the force-based design approach, which still offers the theoretical basis to most of the current practical design codes. The main issue with this approach was the reasonable determination of design eccentricities. In [9], Goel and Chopra first proposed a design eccentricity based on the inelastic torsional behavior of plan-asymmetric structures by considering two performance levels, i.e., serviceability and ultimate limit states. However, their approach may overestimate the strength of relative flexible wall components. To handle this issue, Duan and Chandler [10] suggested a modified design eccentricity that provides optimal ductility requirements and overstrength factors on both flexible and stiff wall components, but it still may underestimate the design eccentricity at the intermediate inelastic stage. Humar and Kumar [11] investigated the effect of wall components perpendicular to the excitation direction based on concepts similar to those proposed in [9,10].The displacement-based design approach has also been researched to properly handle this issue. Since the deformation is a better measurement of structural performance than strength or stiffness, most recently proposed design methodologies adopt this approach. In [12,13], Paulay estimated the required system ductility of an asymmetric structure based on its torsional m...