Seismic strengthening of deficient RC frames using self-centering friction haunches

Local retrofitting of earthquake-prone RC frame beam-column joints with haunches has been recognized as an effective solution to reduce the seismic demand in the joint and redistribute the internal forces in the frame elements. In this paper, an innovative retrofitting method is introduced for upgrading the seismic performance of the RC joints using the Resilient Slip Friction Joint (RSFJ) haunches. On this basis, the RSFJ haunches can preserve the benefits of the conventional haunch retrofitting method while providing reliable frictional energy dissipation, as well as the restoring force for self-centering of the RC frame. Initially in this study, a component experimental testing of the RSFJ is conducted. Also, a detailed numerical model is developed to simulate the performance behaviour of the non-ductile RC joints, which has been further validated by the test results available in the literature. Then, as a retrofitting solution, the RSFJ haunches have been implemented in the model of sample weak interior and exterior RC joints. The results show the capability of the RSFJ haunches in enhancing the strength, stiffness and energy dissipation of the RC joints, as well as decreasing the residual displacement. Accordingly, a retrofit design guide is proposed for the design of the RSFJ haunches in deficient RC frames.