Experimental Testing of Brittle RC frames Strengthened by RSFJ-toggle bracing system

Abstract

This paper investigates the performance of the new retrofitting system, consisting of self-centering damper resilient slip friction joint (RSFJ)-toggle bracing system, as a global retrofitting method for deficient RC frame structures. The RSFJ-toggle bracing system can be activated within small drift values of the frame and preserve the frame from excessive damage. Two scaled deficient RC frames representing typical pre-1970s RC moment resisting frames were constructed and tested to investigate the performance of such retrofitting system. Material testing of the concrete and steel rebars as well as the damper component testing were conducted to gain accurate data for numerical modelling. Recommendations regarding the proper design of various aspects of this retrofitting system were provided, including the brace buckling design, instability consideration for the damper, as well as the overall system, connection detailing and gusset plate design requirements. The experimental observations demonstrate the improved behaviour of the frame in terms of energy dissipation and enhanced stiffness and strength for the upgraded RC frame. As per the findings of this study, the proposed retrofit solution can strengthen the frames within a limited drift and improve the frame’s damping with a repeatable semi-flag shape hysteresis performance.