Experimental Investigation of SPSW Web Plate Stress Field Development and Vertical Boundary Element Demand

Abstract

Steel plate shear walls (SPSW) are an efficient but largely underutilized building lateral force resisting system. The system consists of a moment frame (the boundary frame) with slender steel web plates that are welded or bolted inside the boundary frame, forming a diaphragm. The resulting structure resembles a vertical plate girder. The system resists lateral load primarily through tension field action of the postbuckled web plate. The magnitude and orientation of this tension field is governed by the relative stiffness of the web plate and boundary frame. The 2010 Seismic Provisions currently require that the tension field inclination angle be either 40° or computed using a closed-form equation derived from elastic analysis. It is demonstrated through experimentation and finite-element analyses that the tension field inclination may migrate, from an initially low angle under an elastic postbuckled state, toward 45° as the plate is loaded plastically. The resulting flexural demand on the vertical boundary elements is consistent with this change for both monotonic and cyclic loading. Through a series of small-scale experiments, slender A1008 steel web plates were loaded inside a square reusable pin-connected frame. The aim of this study was to examine the interaction of the web plate with the boundary frame members and the development and change in the web plate tension field orientation. This paper presents the results of the experiments and some of the numerical simulations that were used to study the migration of the tension field orientation angle, and extend the results to a variety of SPSW configurations.