Benefits of expanded ribs on non-seismically designed exterior RC beam-column joints under monotonic loading

Non-seismically designed exterior beam-column joints (BCJs) play a crucial role in nonlinear concrete structures, making an appropriate connection essential. This paper investigates the effectiveness of expanded ribs in non-seismically designed exterior BCJs and compares different connection methods for enhancing their performance. Six BCJ specimens were subjected to monotonic loading in the transverse direction, incorporating expanded ribs (1, 2, 3), couplers, and epoxy bonding, with a structural member using hooked bar anchorage as the reference variable. Load-deflection, load-strain, ductility, energy dissipation, and cracking behaviors were compared, and sectional analyses were conducted to evaluate the suitability of the experimental results. The experimental results showed that specimens with couplers and epoxy bonding exhibited 22.4 and 38.9% lower load resistance, respectively, compared to those with hooked bar anchorage. Moreover, horizontal cracks were particularly observed in the epoxy-bonded specimens along the joint region. When additional ribs were used, the load resistance increased by approximately 1.7-20.5% compared to the reference specimen, with the results indicating that two additional ribs provided the optimal connection. Sectional analyses were conducted to assess the validity of the experimental results and the analytic results showed that the predicted values were about 6.2-28% higher than the experimental results due to the formation of shear cracks in the joint.