Self-Centering Steel Plate Shear Walls: Subassembly and Full-Scale Testing
Clayton, Patricia Marie
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The self-centering steel plate shear wall (SC-SPSW) is a lateral force-resisting system that is capable of providing enhanced seismic performance, including recentering after an earthquake. The primary lateral strength of the SC-SPSW is provided by thin steel infill plates, referred to as web plates, that are connected to the beams and columns. During lateral sway, the web plate resists lateral load through the development of tension field action, and energy is dissipated through ductile yielding of the plate. Unlike conventional steel plate shear walls, the boundary frame in the SC-SPSW employs post-tensioned (PT) beam-to-column connections that are allowed to rock open during lateral sway. If properly designed, the PT connections eliminate damage in the boundary frame and provide restoring forces necessary to recentering the building during an earthquake, thus reducing post-earthquake downtime and repair costs. This research builds upon previous analytical and numerical proof-of-concept studies on SC-SPSWs. Experimental testing was conducted to better understand SC-SPSW behavior and seismic performance. The experimental program consisted of (1) a series of large-scale subassembly cyclic tests to evaluate the impact of various design parameters on SC-SPSW behavior and component demands and (2) full-scale two-story pseudo-dynamic tests to evaluate system performance at three different seismic hazard levels. These tests also investigated possible performance-enhancing variations in SC-SPSW design that were not considered in the previous proof-of-concept study. Post-tensioned column base connections were proposed to eliminate damage in the columns and provide additional recentering. SC-SPSWs with web plates that are only connected to the beams were proposed as a means of mitigating web plate tearing and reducing column demands. Methods for designing PT column base connections and SC-SPSWs with web plates connected to the beams only are presented. Numerical investigations were conducted to evaluate different methods of modeling web plate behavior in SC-SPSWs, ranging from the relatively simple tension-only strip model to the more complex shell element model. When used in cyclic or dynamic analyses, the tension-only strip model was found to significantly underestimate the energy dissipation provided by the web plate, while the shell element model was too computationally demanding for wide-spread implementation. Based on numerical and experimental observations, a modified tension-compression strip model was proposed to conservatively approximate the web plate unloading resistance and the additional energy dissipation it provides. Nonlinear response history analyses were conducted to asses seismic performance of several three- and nine-story SC-SPSW designs. These analyses compared SC-SPSWs with web plates connected to the beams and columns (fully-connected) and SC-SPSWs with web plates connected to the beams only (beam-connected). Results showed that SC-SPSWs using beam-connected web plates had smaller boundary frame members and larger drift demands than their fully-connected web plate counterparts; however, they were still able to meet proposed performance objectives. The numerical simulations also investigated the effects of considering the web plate unloading resistance in the model (e.g. the traditional tension-only model vs. the modified tension-compression model). These analyses showed that considering even small amounts of compression in the strip model significantly reduced drift demands.
- Civil engineering