Shear strengthening of exterior beam-column joints using embedded carbon fibre reinforced polymer bars

Beam-column (BC) joints play an important role in the seismic performance of moment-resisting reinforced concrete (RC) frame structures. Without adequate joint shear reinforcement, as the case is with existing RC frame structures designed according to the pre-1970s building codes, BC joints can be the most vulnerable elements during an earthquake. Several techniques for improving the seismic performance of BC joints have been proposed, but these techniques have been criticised for being labour-intensive and/or susceptible to premature de-bonding. To overcome these shortcomings, a novel technique utilising embedded carbon fibre reinforced polymer (CFRP) bars has been developed for strengthening shear-deficient RC BC joints. Two exterior BC joints were constructed and tested under displacement-controlled cyclic loading. Both specimens were designed to fail in shear. The first specimen is a control specimen designed with inadequate joint shear reinforcement to represent BC joints requiring strengthening. The second specimen was strengthened with CFRP bars embedded within the joint core and epoxied to maintain the bond between the concrete and the embedded CFRP bars. The results show that the strengthened joint had superior global and local behaviour compared to the control one. The shear strength was enhanced by about 40% whereas the enhancement in the shear deformation between 1.50% and 3.00% drift ratios ranged between 20% and 94%. The strengthened specimen also had higher peak-to-peak stiffness, displacement ductility and energy dissipation capacity.