Interlocking shear connectors in steel–ultra-high-performance concrete members

Three shear connectors – steel plates, loop rebars and perforated steel plates (PSPs) – were investigated for steel–ultra-high-performance concrete (UHPC) composite members with internal bracing. Z-shaped push-out tests were conducted to examine failure modes, load–slip responses, shear capacities and resistance mechanisms in normal concrete (NC) and UHPC. The strength of the anchorage material significantly changed the governing failure mechanism. In NC, failure was governed mainly by boundary slip of the interlocking body or local concrete crushing. In UHPC, boundary slip was suppressed, and failure shifted to connector deformation or fracture, local UHPC crushing and shear failure of UHPC short columns inside the openings. The PSP mobilised both end-bearing resistance and mechanical interlocking, providing high capacity at relatively small slip and effective restraint against out-of-plane deformation. Mechanism-based equations were developed, yielding a mean calculated-to-experimental capacity ratio of 0.92 and a coefficient of variation of 0.13. The results support connector selection and shear-capacity assessment in steel–UHPC composite members.