Experimental Comparison of Novel CFRP Retrofit Schemes for Realistic Full-Scale RC Beam–Column Joints

Existing RC moment-resisting frames (MRF) built with inadequate detailing or before the introduction of detailed seismic design codes (pre-1970s) are highly vulnerable to brittle failure mechanisms under earthquake loading. To prevent potentially catastrophic failures and consequent human and economic losses in future earthquakes, efficient and practical retrofit solutions are required for these buildings. This paper presents an experimental study focused on the development of retrofit solutions that adopt carbon fiber–reinforced polymers (CFRP) to improve the seismic performance of existing RC MRF at their beam–column connections. It is highlighted that to date, most experimental studies in this field used simplified test specimens that have ignored the presence of slabs and secondary beams at beam–column connections. This may lead to an unrealistic assessment of FRP retrofit schemes. Hence, in this study, results from six full-scale cyclic tests on typical pre-1970s interior beam–column joints with slab and transverse beams are presented. The tests are used to assess three proposed CFRP schemes composed of a combination of FRP strengthening methods and selective slab weakening. Each scheme is designed to meet a distinct retrofit objective: (1) enhancement of the lateral-load capacity, (2) enhancement of ductility, and (3) enhancement of the lateral-load capacity and ductility, as well as changing the dominant failure mode of the joint from a column hinging mechanism to one where the plasticity is mainly concentrated in the beams. A comparison of the retrofitted specimens with the behavior of a deficient specimen and a specimen designed to modern guidelines highlights the successful achievement of the respective retrofit objectives and the necessity to weaken the slab to achieve a favorable failure mechanism that will allow compliance to be achieved with current retrofit codes.