Anchorage characteristics and their impacts on the seismic performance of HECC/RC composites external beam-column joint

Abstract

In order to enhance the seismic performance and streamline the construction process, particularly in precast frame structures, steel-polyethylene hybrid fiber-reinforced engineered cementitious composites (HECC) is utilized to replace reinforced concrete (RC) in the external beam-column joint core area to form HECC/RC composite joints. In this study, to further alleviate rebar congestion, five no-stirrup reinforced HECC/RC composite external beam-column joints with reduced beam longitudinal rebar anchorage length (i.e., 6d-18d) in core area and one control RC specimen are designed and tested under cyclic loading. Experimental results indicate that anchorage failure occurs until the anchorage of the beam longitudinal rebar decreases to an extremely short length of 6d. In comparison with the control RC specimen, HECC/RC specimens display a reduced bond damage zone and superior bond behavior. Although relatively larger stress is transferred to the anchorage free end when anchorage length is 9d, the beam longitudinal rebar is still effectively anchored without significant slip, indicating that anchorage length of 9d in joint core area may be sufficient which needs further research. In addition, the ultimate bond strength of the rebar embedded in joint core area is lower than that observed in pullout test, underscoring the necessary of considering a safety factor in design anchorage length estimation. Lastly, the contribution of bonding condition on shear force transfer in joint core area is analyzed according to force transfer mechanism, which would promote the determination of the shear capacity of HECC joint. As the bonding damage expanded, the proportion of shear force resisted by truss mechanism decreases, emphasizing the crucial role of adequate anchoring in external joint.