Effects of HSS bar and SFRHSC on seismic performance of interior beam‐column joints: experimental study and shear capacity

The reinforcement congestion in beam‐column joints could be alleviated by using high‐strength steel (HSS) bars, but the bonding property of beam longitudinal reinforcement would be decreased. To address this problem, steel fiber reinforced high strength concrete (SFRHSC) was introduced. Ten interior beam‐column joints, including six HSS‐SFRHSC specimens, three HSS‐HSC specimens, and one normal HSC reference specimen, were tested under reversed cyclic loading. Variables were concreting pattern, reinforcement strength, shear stress ratio, and stirrup reinforcement ratio. The efficiency of HSS bar coupled with SFRHSC on seismic performance was compared based on bearing capacity, energy dissipation, ductility, and bond degradation. Results revealed that HSS reinforced joints with a 25% lower amount of reinforcements showed similar seismic performance when compared with HRB400 bar specimens with identical flexural strengths in terms of failure modes, hysteresis curves, and stiffness degradation, but 12% higher loading capacity, 6.8% larger ductility, and 37.5% greater cumulative energy dissipation. SFRHSC could effectively control cracks, enhance ductility, and increase cumulative energy dissipation due to improved HSS bars bond degradation. The SFRHSC region in the joint had little influence on the seismic performance, but shear stress ratio had an adverse effect on the seismic behavior of interior joints with HSS bars.