DEVELOPING A FULL THREE-DIMENSIONAL MODEL OF SELF-CENTERING CONCENTRICALLY BRACED FRAME SYSTEMS USING NONLINEAR STATIC PUSHOVER ANALYSIS
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A self-centering concentrically braced frame system (SC-CBF) is a bracing system that is developed experimentally and numerically, designed to increase the drift capacity of the braced frame before damage and reduce the residual earthquake drift. The development of the SC-CBF system originated from the conventional concentrically braced frame” (CBF) system, which has been widely used as a lateral-load-resisting system in low- to mid-rise structures. The SC-CBF system displays improved performance than a CBF system when subjected to design basis earthquake. The numerical models that have been used to study the SC-CBF system have been two-dimensional models, throughout a variety of research studies that have investigated the performance of SC-CBFs. Developing the SC-CBF system in a three-dimensional model allows further study of parameters that could affect the dynamic response of the SC-CBF system. The three-dimensional SC-CBF model (FULL 3D SC-CBF) is formulated using OpenSEES, with all structural members found in the building (e.g., SC-CBFs oriented perpendicular to the direction of loading, beams and columns of the gravity system). However, the FULL 3D SC-CBF model contains four SC-CBFs in each axis of the building, built symmetrically and modeled in different geometric configurations for further investigation in structural behavior that further assesses the behavior of the SC-CBF system. Different geometric configurations of the SC-CBF system are modeled to investigate the effect of different ways to model the gravity system alongside the SC-CBF system. In addition, five parameters studied are varied and analyzed in comparison to the FULL 3D SC-CBF, including the different friction coefficients at the lateral-load bearings, the change of connection rigidity throughout the gravity system (with or without moment resistance), the fixity of the gravity column bases, the gravity column flexural rigidity, and P-Δ versus corotational second-order moment calculations. Studying the effect of these different parameters can guide a designer toward the most effective way to utilize the SC-CBF system to efficiently resist lateral loading in seismic applications. This study concludes that the SC-CBF system behavior can be achieved in a fully three-dimensional model. However, these models require a significant computational effort, and should be used predominantly for in-depth modeling analysis. Additionally, the 3-D models can be employed to understand the impact of a variety of gravity system parameters in the behavior of the SC-CBF system.