Construction and Steel Structure

Buildings with traditional structural systems experience large residual deformation after a large magnitude earthquake, and often lose serviceability and need to be demolished incurring huge economic losses. In order to resolve this issue, various smart structural systems have been developed by researchers. One such system is the novel piston based self-centering bracing (PBSC) system. This study investigates the cyclic performance of this bracing system to determine 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 its self-centering mechanism. During cyclic tension-compression loading, the bars are pulled from opposite directions in order to avoid compressive loading on the bars. The energy dissipation is achieved through nonlinear load deformation hysteresis. Furthermore, the PBSC bracing system is designed to be fully buckling restrained. The system exhibits flag shaped force deformation hysteresis. A novel hysteresis model is proposed from the simulated hysteresis response of the PBSC bracing system. This hysteresis model is implemented in a commercial structural analysis and design software called S-FRAME. Then the seismic performance of braced frames equipped with such PBSC bracing system has been evaluated. First, overstrength and force reduction factors are determined using FEMA P695 methodology. Using these factors, PBSC braced frames are designed and their seismic performance is evaluated in terms of inter-story drift responses and also compared against buckling restrained braced frames using fragility function. Finally, this research presents a step by step design methodology for the PBSC bracing system.