UBC Theses and Dissertations
Innovative spring & piston based self-centering bracing systems for enhanced seismic performance of buildings Issa, Anas Salem
Concentric Braced Frames (CBFs) are commonly used for lateral load resistance in buildings. Buckling, however, is a significant concern for CBFs where they lose their strength and stiffness when subjected to load reversals during earthquakes. To tackle this problem, a novel easy-to-fabricate low-cost Spring Based Piston Bracing (SBPB) system was developed with single and double friction spring configurations. In this system, a brace member is able to carry a large magnitude of tension and compression forces where a special spring was installed in the piston cylinder. In parallel, another system was investigated which is the novel Piston Based Self Centering bracing (PBSC) system, which employs Nickel Titanium (Nitinol) based Shape Memory Alloy (SMA) bars instead of friction spring, for its self-centering mechanism, inside a sleeve-piston assembly. The energy dissipation was attained through nonlinear load deformation hysteresis. self-centering stable hysteresis behavior was achieved when both systems are subjected to qualifying quasi-static loading. Strain rate effect was also assessed experimentally, and comparable results were achieved without any performance degradation. Numerical simulation shows excellent matching with the test results. Twelve reference braced steel buildings (4 storeys, 6 storeys, 8 storeys, and 12 storeys) were designed utilizing Buckling Restrained Braces (BRBs), SBPB, and PBSC braces and their performances were compared in terms of interstorey drift and residual drift. The proposed systems experienced zero residual deformations, but relatively larger drift values compared to BRBs. Over 1500 inelastic pushover and incremental dynamic analyses were performed to assess the lateral capacity and generate a wide range of fragility relationships for the reference structures. Displacement-based protocols generated from dynamic simulation of a reference building were obtained, scaled down, and applied for the fabricated brace specimen. The experimentally generated hysteresis response is scaled up and compared again to the original response to reduce the time and effort of conventional shake table testing, hybrid simulation, or quasi-static testing. Excellent agreement between the numerical and experimental results was achieved in the closed-loop dynamic simulation and testing.
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