CFRP Rehabilitation of Concrete Frame Joints with Inadequate Shear and Anchorage Details

TLDR

Externally bonded FRP retrofits have proven effective for deteriorating RC structures, yet their application to building beam‑column joints with deficient shear reinforcement—especially full‑scale connections—has been limited and poses a risk of catastrophic collapse during earthquakes. This study investigates whether CFRP rehabilitation can upgrade deficient beam‑column joints to improve their seismic performance. Full‑scale cyclic tests were conducted on existing beam‑column joints with pre‑1970s reinforcement details, varying CFRP retrofit configurations and column axial loads to assess their effect. The retrofitted joints exhibited markedly higher shear capacity, reduced slippage of short embedded beam reinforcement, and overall enhanced structural performance compared to as‑built specimens.

Abstract

The research presented in this study involves full-scale experimental evaluation of carbon fiber-reinforced polymer (CFRP) rehabilitation for existing beam-column joints designed for gravity load with common pre-1970s deficient reinforcement details when subjected to cyclic loading. Numerous studies have demonstrated effectiveness of externally bonded fiber-reinforced polymer (FRP) materials for retrofitting the deteriorating RC structures. Although these materials are widely used in bridges, their applications in buildings have been somewhat limited. In particular, the experimental investigations on external FRP retrofit of deficient beam-column joints have not thoroughly been investigated and they are mainly on scaled-down specimens. The failure of these subassemblies, which possess lack of shear reinforcement within the joint core and shortly embedded positive beam reinforcement, would possibly result in catastrophic collapse of reinforced concrete frame structure during an earthquake event. Recognizing the urgent need to upgrade these structural subassemblies, the current investigation uses CFRP retrofit techniques to enhance the performance of such deficient joints. Experimental variables studied entail the developed CFRP retrofit configurations, and magnitude of the applied column axial load. Comparative analysis of the lateral loads versus drift hysteresis loops, stiffness degradation, and total dissipated energy curves of three as-built and three corresponding CFRP-retrofitted RC joints revealed that significant improvement in the shear capacity of the upgraded joints occurred. More importantly, the slippage of short embedded beam positive reinforcement into the joint was substantially controlled due to the developed CFRP retrofit. The results demonstrate the effectiveness of CFRP retrofit configurations in enhancing the structural performance of actual size connections.