Experimental investigation on the effect of hoop spacing and crosstie configuration on the cyclic performance of reinforced concrete beams

According to ACI 318-19(SI), in the plastic hinge zone of RC beams, the longitudinal reinforcement at each corner and every other longitudinal reinforcement must be enclosed by the corner of the closed hoop or the hooks of crossties. However, in RC construction practice, the longitudinal reinforcement of RC beams is densely arranged, making construction difficult. In this study, four large RC beam specimens were designed and fabricated to conduct experiments to verify the effect of hoop spacing and crosstie configuration on the cyclic performance of reinforced concrete beams. It is found that: (1) The crosstie configuration with seismic hook engaging the longitudinal reinforcement at the bottom is recommended and that during construction, within the range of twice the beam depth from the RC column outer face, the bottom and side formwork should be completed after the crossties are assembled, which should solve the problem of difficult construction. (2) The transverse reinforcement spacing between 4 and 6 times the smallest longitudinal reinforcement diameter of RC beams may have no significant effect on the cyclic performance of RC beams. (3) The requirement that in the plastic hinge zone of RC beams, every corner and alternate longitudinal bar on the perimeter must have lateral support provided by the corner of a tie or crosstie in ACI 318-19(SI) may not have a major impact on the cyclic performance of the RC beam. (4) The ultimate drift angle of each specimen in the negative direction was between 4.3% rad and 4.5% rad; thus, all the specimens satisfied the ACI requirement. However, the cyclic performance (plasticity rotation angle) of all specimens basically did not meet the requirement of 3.0% rad for earthquake-resistant structures.