Optimization Based Seismic Design of Self-centering Concentrically Braced Frames

This paper presents a design approach for multiple rocking Self-Centering concentrically Braced Frames (SC-CBFs) using a zero-order optimization framework. The objective of the design is to minimize the construction cost of the SC-CBF while satisfying performance constraints. The design space includes the properties of the rocking sections while the elements of the structural system are indirectly considered. In addition, the optimization problem is formulated to eliminate unnecessary rocking sections. Due to the nonlinearity of the optimization problem, an iterative procedure is adopted. Each iteration includes a set of new candidate designs of the system which are a product of the optimization algorithm used. The response of each design is computed using a nonlinear time history analysis (NLTHA) utilizing the Mixed Lagrangian Formalism (MLF). MLF has been shown as an efficient numerical scheme for this type of problem. The proposed methodology has been applied for the seismic design of SC-CBFs with multiple rocking sections. The results show that the optimized structures satisfy the predefined allowable performance levels with reduced construction costs.