Experimental study of HSS-reinforced exterior beam–column joints with different enhancement details

Abstract

High-strength steel (HSS) bars are used as beam and column longitudinal reinforcements to reduce the amount of bars and thereby, prevent reinforcement congestion and insufficient concrete compaction. However, the use of high-strength steel reinforcements may induce bond failure of beam steel bars. To improve joint performance, steel fiber-reinforced high strength concrete (SFRHSC) and X-shaped reinforcement are proposed. Six full-scale specimens reinforced with steel fiber-reinforced high strength concrete and X-shaped reinforcement were designed and tested under reverse cyclic loading. The main parameters included the enhancement details, shear compression ratio, and concrete patterns. The seismic performance of the tested exterior beam–column joints (BCJs) was evaluated based on the cracking patterns, load capacity, energy dissipation, and ductility. The test results revealed that the combination of steel fiber-reinforced high strength concrete and X-shaped reinforcement significantly improved the loading capacity and energy dissipation. This was attributed to the enhancement of the shear by the X-shaped reinforcement, regulation of crack propagation by the steel fibers, and confinement of the joint core concrete by stirrups. Although the specimens displayed shear failure in the joint core area, both X-shaped reinforcement and steel fiber-reinforced high strength concrete could improve the failure modes. Here, steel fiber-reinforced high strength concrete was more effective. The bond performance of the beam longitudinal reinforcements was investigated to study the strain of the reinforcements, degradation of the bond stress, and slippage of the beam reinforcements. Anchorage methods of national codes were compared, and an anchoring recommendation was put forward.