NONLINEAR SEISMIC PERFORMANCE OF SELF-CENTERING ECCENTRICALLY BRACED FRAME STRUCTURES WITH REPLACEABLE HYSTERIC DAMPER
Keivan Esfahani, Arshia
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The focus of this dissertation is on numerical simulation study of self-centering eccentrically braced frame (SCEBF) buildings subjected to seismic ground motion. Self-centering EBF with replaceable fuse devices can be designed to provide the strength and stiffness comparable to conventional steel EBFs while maintaining plumbness and sustaining repairable structural damage concentrated to seismic fuse devices under design basis earthquakes. This study aims to investigate the seismic system behavior of three common configuration types of self-centering EBFs including the K-type, D-type, and Y-type SCEBFs. Analytical formulas are derived for the key strength and stiffness values of these three types of SCEBF module frames. Two different types of finite element models, one with refined meshes in ANSYS and another with primarily frame members in SAP2000, are developed and calibrated with experiment data. Comparison with analytical results further verifies the finite element models. In addition to nonlinear static analysis results, the nonlinear time history analysis results show that residual drifts of the SCEBFs are negligibly small and damages in the structure are concentrated to hysteric damper under design basis earthquakes. Additionally, a parametric study of the three types of SCEBFs with three different levels of PT cables’ initial stress has been done to validate the approach to tuning the self-centering EBF’s seismic behavior. The parametric study results suggest that key structural parameters such as the equivalent yield strength and the post-gap opening stiffness of SCEBFs can be adjusted through properly selecting post-tensioning cable’ length and initial stress levels. A new metallic hysteric damper called TPAD was developed to be utilized in proposed SCEBF structures. TPAD is a trapezoidal plate connected to a round rod, and its design is inspired by the design of TADAS devices . It is optimized based on fracture investigation  through parametric studies. In parametric studies, cyclic loading has been applied to TPADs with different properties to investigate the overall behavior of TPADs. It is found that TPAD’s height (h), slope ratio (α) and thickness (t) significantly affect the ductility of TPAD.