Seismic retrofitting of RC-frames using Resilient Slip Friction Joint toggle-bracing system

Abstract

Seismic retrofitting of the current non-ductile or limited ductile RC buildings is one of the challenging design topics among the scholars and engineers. The common technique for RC-frame retrofitting involves adding conventional or dissipative yielding braces such as BRBs to the system. Through these additional braces, the overall stiffness and strength of the frame increase. By yielding of these braces prior to excessive plastic deformations in the RC-frames a portion of the seismic energy would be absorbed, resulting in limiting the overall drift and alleviating the damage on the main RC frame. This paper introduces an alternative method for retrofitting of RC-frames, using Toggle-Bracing system, equipped with self-centering damage-free Resilient Slip Friction Joints (RSFJs). The RSFJ-Toggle bracing can limit the story drift for the frame and increases the overall strength and stiffness of the system, while magnifying the small floor displacement for the joint to dissipate the seismic energy. It can also provide restoring force for the frame, in case of extreme seismic events. In this paper, firstly, the results of the RSFJs component testing are presented. Secondly, the performance of the RSFJ-brace assembly is studied through hysteresis performance of a numerical model of a RC-frame with and without RSFJ-Toggle bracing system. Finally, the recommendation for brace to RC frame connections are briefly provided, as well as stability considerations to prevent buckling of the brace system.