Optimum distribution and design of friction-damped diagonal brace for reducing seismic damage of steel moment-resisting frames

Retrofitting buildings using friction-damped diagonal brace (FDDB), as one of the passive control systems, can substantially improve their seismic performance. The distribution of FDDBs along the height of a building is known as a critical decision. This study proposes the optimum distribution and design of FDDBs through a seismic damage-based approach. For this purpose, the seismic damage based on the Park-Ang damage model is chosen that represents seismic deformations and cumulative hysteretic energy dissipated in structural members. The objective function is to minimize the average maximum story damage under seven scaled earthquake excitations. A constraint is imposed to obtain the uniform distribution of story damage while controlling the maximum axial force of brace in FDDBs. A hybrid of the real and binary particle swarm optimization algorithms is developed to solve the optimization problem. Two inelastic steel moment-resisting frames (SMRFs) equipped with a specific number of FDDBs are presented to demonstrate the proposed approach. Results show that the optimized FDDBs-equipped SMRFs sustain the most uniform distribution of damage. In addition, seismic fragility assessment indicates that the optimum FDDBs significantly reduce the probability of failure of the controlled SMRFs at different performance levels.