Relocating the plastic hinge at beam column joint interface into the beam in CFRP strengthening

Reinforced concrete buildings with moment resisting frames and beam-column joints (BCJ), designed prior to introduction of seismic codes, are deficient when subjected to lateral seismic loading. The weakest link in these buildings, the BCJ fail in shear under lateral seismic loads resulting in irreparable damage to the buildings and possibly a collapse. Several strategies for shear strengthening deficient joints in old buildings have been investigated and implemented in buildings over the past three decades using CFRP sheets and laminates. The shear failure in joints is successfully precluded, with the failure mode shifting to the formation of a plastic hinge at the BCJ interface. A localized failure in the connecting beams away from the joint is a more preferable failure mode rather than a plastic hinge formation at the interface. In modern BCJ with high strength concrete and shear reinforcement in joints, the plastic hinge is also formed at the BCJ interface, which is again undesirable failure mode. It is highly appropriate that all BCJ should undergo a flexural-shear failure with the plastic hinge formation away from the BCJ interface well into in the connecting beam. Based on a nonlinear finite element investigation of CFRP strengthened shear-deficient BCJ using concrete damage plasticity model in ABAQUS, experimental investigations have been conducted. The experimental investigation shows that in BCJ strengthened in shear, an appropriate scheme of CFRP strengthening results in improved ductility, energy dissipation and an increase in load capacity with a movement of the plastic hinge formation from the BCJ interface to a distance inside the beam.