THE INELASTIC SEISMIC RESPONSE OF STEEL PLATE SHEAR WALL WEB PLATES AND THEIR INTERACTION WITH THE VERTICAL BOUNDARY MEMBERS
Webster, David John
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The steel plate shear wall (SPSW) is a building lateral force resisting system that comprises a moment frame (the boundary frame) and slender steel diaphragms (web plates) welded or bolted inside the boundary frame. The system resists lateral load primarily through tension field action in the web plates. Web plate forces are anchored by the boundary frame members. The Seismic Provisions currently require the boundary members to be capacity designed assuming the web plate has fully yielded in tension and forms a pure tension field at a prescribed angle computed from an elastic analysis. In design, web plates are frequently modeled as a series of parallel, inclined tension-only truss elements. This research focused on the development and magnitude of in-plane web plate stresses due to seismic demands and how these are transferred to and resisted by the boundary frame, specifically the vertical boundary members, or elements (VBEs). The evolution of web plate stress is controlled by the material properties, slenderness ratio, hardening behavior, web plate aspect ratio and cyclic drift history. Several small-scale cyclic tests of steel web plates were conducted to investigate the hardening, pinching and snap-though behavior, and to validate observations made in numerical studies that the tension field inclination angle migrates to a fixed value close to 45 degrees as the web plate is loaded plastically. Using statistical methods, the magnitude of hardening expected for typical web plate materials was then estimated for the MCE level earthquake. The results of the experiments and ABAQUS analyses of single story SPSWs are used to develop and implement a new OpenSees uniaxial material model, SPSW-WP, to be applied to truss elements, specifically for SPSW applications. The material was designed to mimic the effects of in-plane web buckling and accurately capture the effects of material hardening, stiffness degradation, residual shear strength, web plate slenderness and correctly model the reloading drift under cyclic loading conditions. The model is calibrated using ABAQUS analyses of single story SPSWs with a range of material hardening characteristics and geometries. It is then validated using both ABAQUS models and with cyclic test data. Finally the new material model is incorporated into the analyses of two six-story SPSWs; one utilizing slender A36 steel web plates, and one with stocky, low yield point LYP100 steel web plates. The story drift demands and VBE demands are compared and contrasted with ABAQUS analyses of the equivalent structures for four DBE and four MCE level ground motions. Web plate hardening and changes in the tension field inclination angle were found to be significant but had only a moderate influence on VBE demands. The use of stocky web LYP plates enhances lateral stiffness, reduces story drifts and reduces VBE demands when compared with more commonly used slender A36 web plates of lower net tensile strength.
- Civil engineering