OPTIMAL SEISMIC RETROFIT OF STEEL MOMENT-RESISTING MOMENT USING BRACING-FRICTION DAMPER SYSTEMS

Abstract

Bracing-friction damper system (BFDS), one of passive control devices, consists of a Pall friction damper added in-line with a diagonal, which is utilized for the seismic retrofit of building structures. The BFDS can dissipate the input energy of earthquakes and mitigate a considerable amount of the hysteretic energy of structures. This study presents the optimal seismic retrofit of inelastic steel moment-resisting frames (SMRFs) through the optimum design of the BFDSs installed in each story of SMRFs. For this purpose, minimizing the maximum damage index of stories averaged over seven scaled earthquake excitations is selected as the objective function so that the story damage is uniformly distributed along the height of SMRFs. The damage index is calculated based on the Park-Ang damage model which is expressed based on a linear combination of deformation, moment, and absorbed hysteretic energy of structural elements imposed by an earthquake excitation. The results indicate that the optimized BFDSs-equipped SMRFs exhibits the better distribution of story damage than that of uncontrolled SMRFs. Finally, the seismic assessment of SMRFs is done by the fragility analysis. The results of the seismic fragility assessment demonstrate that the optimized BFDSs improve the seismic performance of retrofitted SMRFs compared to that of uncontrolled SMRFs at different damage states.