Seismic performance and shear strength of HECC/RC beam-column joints with simplified reinforcement

The application of high-performance materials presents an effective strategy to enhance the performance of structural components. To improve the seismic behavior and ductility of beam-column joints while mitigating reinforcement congestion, a high-performance hybrid fiber reinforced (1 % vol polyethylene fibers and 1 % vol steel fibers) cementitious composite (HECC) was applied in the joint core region. Five HECC/reinforced concrete (RC) composite joint specimens considering stirrup ratio in the core region, axial compression ratio, and HECC strength were designed and tested in this study. The results demonstrated that the application of HECC significantly enhanced the ductility characteristics during shear failure in the joint core region, achieving a shear capacity reserve 34 % greater than that of conventional RC joints. In addition, the specimens maintained structural integrity after failure, with micro-cracks being distributed more uniformly. Unlike RC joints, the contribution of transverse rebars on the bearing capacity of HECC joint was less significant, as evidenced by only a modest 7 % increase in bearing capacity at a 2.10 % stirrup ratio, indicating that the fiber bridging effect of HECC provided a constraint effect similar to that of transverse rebars. Furthermore, existing calculation formulas tend to significantly underestimate the shear capacity of HECC joints. Therefore, a revised formula was proposed to enhance an existing model for HECC beam-column joints by incorporating a synergistic enhancement coefficient. This modification improves accuracy in predicting the shear strength of HECC joints, achieving an average predicted-to-test ratio of 1.013 and a coefficient of variation of 0.096.