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Concentrically braced frame (CBF) systems have limited capacity for lateral displacement, causing structural damage that leads to high post-earthquake costs under moderate earthquakes. Self-centering concentrically braced frame (SC-CBF) systems have been developed to soften the lateral force-lateral drift response of the system without causing structural damage; however, the construction cost of SC-CBF systems is expected to be high due to the precision required in fabrication and erection. To take advantage of the ductility of SC-CBFs and the economy of conventional CBFs, a novel dual system has been proposed in which the lower stories of the lateral force resisting system are SC-CBFs and the upper stories are conventional CBFs. The SC-CBF is intended to act as a ductile sub-structure for the CBF, reducing the construction costs and post-earthquake costs. This study presents the design basis of the dual system and an investigation of the influence of dual system configuration on structural performance. To achieve this goal and demonstrate the effectiveness of the proposed dual system, a probabilistic performance assessment is conducted in this study, considering both structural and non-structural components. Firstly, eight prototype buildings are designed with the same configurations and gravity systems but different lateral load resisting systems (CBF and dual systems). Then, nonlinear time history analysis is performed using 3D numerical modeling to obtain seismic responses under a suite of ground motions. Next, probabilistic demand models are developed to predict the selected engineering demand parameters. To develop probabilistic demand models, several intensity measures are investigated to determine the best link between ground motion properties and structural and non-structural responses. The demand model parameters are estimated from regression analysis based on the responses obtained from nonlinear time history analysis of the finite element models. Moreover, hazard analysis is performed to quantify the seismic hazard for the structures. Three different locations inside the United States are considered in the hazard analysis: Los Angeles (high-seismic zone), Seattle (moderate-seismic zone), and Boston (low-seismic zone). Using detailed demand models, the corresponding capacity limits, and calculated intensity hazards, seismic fragility curves and engineering demand hazard curves are developed for three performance levels for structural and non-structural components. Finally, loss analysis is conducted to estimate expected annual loss and pay-off periods for different structural systems. The results of this study show that the dual system can be an efficient structural system for mid-rise buildings in high-seismic zones. Moreover, the time in which the higher initial construction costs of the dual systems are compensated by lower earthquake-induced losses in the lifetime of structures is calculated and presented for different configurations of the dual system. |
