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UBC Theses and Dissertations

Seismic performance evaluation and design of a novel piston based self-centering bracing system Haque, A. B. M. Rafiqul


Buildings designed and constructed using current seismic design codes experience nonlinear deformation during strong earthquakes; resulting in hysteretic damping. This behavior is necessary for dissipating energy from an earthquake. Thus, buildings with traditional structural systems experience permanent deformation after seismic events, resulting in enormous economic losses. To resolve this issue, researchers have developed various smart structural systems in the past decades. One such system is the novel piston based self-centering bracing (PBSC) system. This study investigates the cyclic performance of this bracing system in finite element environment to predict its load-deformation response during seismic events. This newly developed bracing system utilizes Nickel Titanium (Nitinol) based shape memory alloy (SMA) bars inside a sleeve-piston assembly for the self-centering mechanism. During cyclic loading, the bars are pulled from opposite directions to avoid compressive loading on the bars. The energy dissipation is achieved through nonlinear load deformation hysteresis. Furthermore, this bracing system can be designed to be buckling restraint. The system exhibits flag shaped force-deformation hysteresis. A unique hysteresis model is proposed from the simulated hysteresis response of this bracing system. This hysteresis model is implemented in a commercial structural analysis and design software known as “S-FRAME.” In the next phase, seismic performance of steel frames equipped with the PBSC bracing system has been evaluated. Overstrength and force reduction factors were determined using FEMA P695 methodology. Using these factors, PBSC braced frames were designed and their seismic performance was assessed in terms of inter-story drift ratios. Furthermore, the seismic performance of PBSC braced frame was also compared against buckling restrained braced frames in terms of fragility function. Finally, this research presents a design methodology for this bracing system.

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