Mechanical characteristics of a novel composite slab: Experimental and numerical investigation

The steel tube slab (STS) pipe-roof structure is an innovative support system for subway station construction, comprising steel tubes, flange plates, concrete, and bolts. Traditional ‘load-beam’ models contradict the concept of pipe-roof structures as protective cover slabs, while existing ‘load-plate’ models remain limited to the elastic stage. This study combines laboratory tests with numerical simulations to investigate the full-range stress mechanism of an STS composite slab, addressing the design challenges in the inelastic stage. Key scientific findings include: The slab transitions from uniaxial to biaxial loading when the aspect ratio λ (the ratio of the longitudinal span and the transverse span) falls below 1.0, with superior longitudinal bending resistance compared to transverse performance. System ductility predominantly depends on transverse deformation capacity, while significant stress redistribution occurs among steel tubes, flange plates, and confined concrete. Intra-tube concrete functions as a primary longitudinal load-bearer under effective confinement, whereas inter-tube concrete acts mainly as a lateral connector. Steel tube thickness governs both stiffness and bearing capacity (10–50% influence), followed by λ (3–13%) and flange plate thickness (2–12%), with bolt diameter showing negligible impact (<1%). Optimized parameters are established: 8 mm steel tube thickness, 4 mm flange plate thickness, 4 mm bolts, and a λ of 1.0 (laboratory scale; scaling required for prototypes). These findings provide a rational basis for the inelastic design of STS pipe-roof structures and reveal the orthotropic plate behavior of this novel composite system.