Seismic performance of stirrup-free HECC/RC interior joint: feasibility of shortening and simplifying beam reinforcement anchorage

To simplify reinforcement detailing and enhance anchoring behavior, steel–polyethylene hybrid fiber-reinforced engineered cementitious composites (HECC) were applied in the joint core region instead of conventional concrete. Four stirrup-free HECC/RC interior joints featuring varying beam reinforcement anchorage lengths (7d, 9d, 11d, 15d) and two anchoring methods (continuous through the joint and overlapping) were designed and tested. Experimental results revealed anchoring failure when the beam reinforcement anchorage length was reduced to 9d. The incorporation of HECC significantly mitigated damage within the core region and improved the overall performance of the joint. Notably, even with the complete removal of stirrups, no delamination of the cover layer or crushing of HECC was observed in the core region. Insufficient anchorage diminished load-carrying capacity, accelerated bearing capacity degradation, and lowered the energy dissipation of joint specimens. In addition, the bond damage of continuous longitudinal reinforcement was more severe than that of the straight anchored one, resulting in increased slip of the beam reinforcement. Based on seismic performance and bond stress-slip analysis, a beam reinforcement anchorage length of 15d was recommended to maximize HECC’s exceptional bonding performance and ensure the seismic reliability of joint. Finally, a formula with acceptable accuracy for the shear bearing capacity of stirrup-free HECC interior joint, accounting for the influence of fiber reinforcement, was established based on the diagonal compressive strut mechanisms.