Experimental study of externally flange bonded CFRP for retrofitting beam-column joints with high concrete compressive strength

One of the methods used to design reinforced concrete buildings against lateral forces is the use of moment resisting frames which comprises of beams, columns, and the interconnection of beam-column joint. The weakest link in this type of structure is the beam-column joints (BCJ). The BCJ are important for framing action for gravity loads, lateral loads, and combination of both, though, it is the lateral loads that place the largest demands on BCJ. If BCJ could regain their original shape and strength with a minimum repair after an earthquake, then the problems associated with permanent damage could be mitigated. Of the numerous ways to retrofit or repair a deficient BCJs is the use of carbon fiber reinforced polymer (CFRP) composite. Most of the work done on strengthening with CFRP are by applying the CFRP sheets on the web and around the BCJs for shear strengthening, while little has been done on strengthening of BCJs for flexural-shear failure. Hence this research studies the behavior of BCJs made with concrete of compressive strength in the range of 50-60MPa, without shear reinforcement at the joint. The effectiveness of CFRP in retrofitting such BCJ using externally flange bonded CFRP by relocating the plastic hinge from the interface of the BCJ to a distance inside the beam. It was observed that such BCJ failed in flexure, with plastic hinge formation at the interface of the BCJ, followed by yielding of the beam flexural reinforcement. The retrofitted samples, showed improved ductility, load carrying capacity, with the plastic hinge moved from the interface of the BCJ to the termination point of the CFRP on the beam.