Study on Flexural Behavior of Large-Span Precast Ribbed Concrete Composite Slabs for Underground Subway Stations

［Objective］ The large-span precast ribbed concrete composite slabs for underground subway stations have problems of thick slabs, large spans, and heavy self-weight. And there are few related researches at present, necessitating studies on the mechanical properties of the slabs and factors that affect them. ［Method］ The composite roof slab of a prefabricated subway station on Jinan Metro Line 8 is studied with combination of experiments and numerical simulations. Two composite slab specimens and one cast-in-place slab specimen are designed for static loading tests, and the crack distribution and development of the specimens, as well as the load-midspan deflection curves are analyzed. Numerical simulation of the test conditions is carried out. An extended analysis of key factors affecting the mechanical properties of the composite slabs is carried out on the premise of verifying the feasibility of the finite element model. ［Result & Conclusion］ The stress state of three specimens in the loading process are similar. During the loading process, the composite slab specimens do not slip along the composite surface, penetrating development of the cracks on the slab side occurs, the bond performance of the composite surface and the overall specimen working performance are good; the upper reinforcement of the bottom slab rib assumes part of the tensile reinforcement role, which improves the load carrying capacity of the composite slab. Because the setting of truss reinforcement has limited effect on the load carrying capacity improvement of the composite slab, the density of truss reinforcement can be reduced or the setting of truss reinforcement can be canceled according to actual conditions; the use of a hollow bottom slab can effectively reduce the self-weight of the composite slab without having much effect on its stress performance.