Direct displacement-based design of dissipative bracings for seismic retrofit of reinforced concrete buildings

Abstract

A non-iterative direct displacement-based method is proposed for the design of dissipative bracings for seismic retrofit of gravity-load-designed (GLD) reinforced concrete (RC) frames. The design methodology aims at limiting the interstorey drifts of the GLD frame to prevent damage in the existing columns, by appropriately designing both stiffness and damping of the bracings. The method is based on a simplified yet accurate representation of the braced frame, through a so-called stick model, whose elements stiffness and damping are obtained by equivalent linearization of each braced storey. This allows performing a simplified modal analysis and obtaining an optimal design of the bracing system at each storey, both in terms of stiffness and damping. The design method efficiency has been validated by assessing the obtained performance of three GLD RC frames retrofitted with bracing systems and by comparing the outcomes with two other design methods available in the literature.