Direct displacement-based design of hysteretic bracings for retrofitting of reinforced concrete buildings

Abstract In this study, a direct displacement-based method is proposed for the design of hysteretic dissipative bracings to be applied to gravity-load-designed (GLD) reinforced concrete (RC) frames. The direct, i.e., non-iterative, design procedure aims at limiting the interstorey drifts of the GLD frame to prevent damage in the existing columns, thanks to the added 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. The method allows 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 comparing the performance of three GLD RC frames retrofitted with bracing systems designed with two other methods available in the literature.