Seismic performance improvement of buildings with self-centering bracings

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Bracings are diagonal structural elements in a building for resisting lateral loads. Traditional bracings essentially carry axial loads. They perform well under axial tension. However, under compression, braces tend to buckle and lose their load carrying capacity. Researchers have proposed buckling restrained bracing, yielding bracing, etc to overcome this buckling problem. However, their disadvantages including: a) heavy weight, b) fabrication difficulty, and c) potential permanent damages after an earthquake. Here, novel bracing systems are proposed to overcome these shortcomings. These systems will be light-weight, and will remain operational with no permanent damages even during a large earthquake. The proposed system will utilize superelastic shape memory alloy (SMA) bars installed inside a cylinder piston, or SMA plates in confined rubberized concrete assembly. A properly designed self-centering braced frame structure is expected to remain operational even after a large seismic event due to its self-centering capability, increasing safety and survivability. It will also provide large savings in reduced repair/replacement work necessary in a post-disaster scenario, and potential for remediation in place rather than demolition. The significance of this research is paramount as this novel technology will help Canada improve the level of safety of building infrastructure during earthquakes. The first stage will involve evaluating the mechanical properties of SMA bars/plates and performance of couplers that connect SMA to steel parts. A series of large-scale quasi-static cyclic and dynamics tests will be performed on bracing elements and braced frames. The generated experimental data will be employed to determine the important parameters that affect the seismic response and limit states, which will help develop performance-based design guidelines for braced frames. The proposed design guidelines will be validated with hybrid simulation tests. The research team will work closely with the partners and design code committee to formulate the appropriate framework with which the proposed design recommendations can be incorporated in the design codes.