Punching shear resistance and failure mechanisms of Steel-UHPC/ECC composite slabs

This study investigates the application of ultra-high-performance concrete (UHPC) and engineered cementitious composites (ECC) in a newly proposed single steel-plate–concrete (SC) composite slab system. The novelty of this research lies in introducing UHPC/ECC into a single-plate SC configuration and experimentally revealing its distinctive two-stage punching–membrane load-transfer mechanism. Six SC slab specimens with different concrete types and shear connector layouts were tested under concentrated static loading to evaluate their failure modes and structural responses. Compared with normal concrete, UHPC and ECC increased the ultimate punching shear capacity by up to 27.9% and 18.2%, respectively, and enhanced post-peak deformability by 33–76%, while transforming the failure mode from brittle punching to a more ductile steel-plate–controlled response. Finite element simulations further clarified the internal stress distribution of shear connectors, the evolution of the punching cone, and the confinement provided by the steel plate. Based on the combined experimental and numerical insights, predictive models for punching shear strength were developed by incorporating composite action and fiber-bridging effects. The proposed models show good agreement with test results, with a mean predicted-to-measured ratio of approximately 0.97–1.08 and a coefficient of variation within 17%, demonstrating their suitability for engineering design.