| For the traditional pipe-roofing method, the steel tubes were connected by an interlock in the transverse direction, and the stiffness of transverse lock connection between the tubes is relatively low. Thus, during excavation the stability of pipe-roofing system was ensured by longitudinal flexural strength of concrete filled steel tube and temporary supporting system. The tedious steel supporting structure and complex conversion of mechanical system in traditional pipe-roofing method may often give rise to an inconvenience for the construction activities. To overcome the problem mentioned above, an improved pipe-roofing structure, also known as Steel Tube Slab (STS) structure is proposed to construct a subway station. It is helpful to improve the transverse load-carrying capacity of traditional pipe-roof by adding transverse high strength bolts and flange plate between the tubes, and the temporary support were not required during the excavation. This paper choosing a super-shallow buried subway station constructed by STS structure as a background engineering, aims to investigate the mechanical properties of STS structure using model test, numerical simulation and theoretical analysis. The main research contents were summarized as follows:The failure mode and mechanical characteristic of STS structure under four-point bending test were investigated, which aims to analyze the effect of spacing between the tubes, flange thickness, transverse connection mode, concrete compressive strength, reinforcement of high strength bolts and loading modes on the load-carrying of STS structure. The rusults showed that welding of bottom flange have most significant effect on the load-carrying capacity of the STS structure. The spacing of tubes and flange plate thickness has certain effect on the load-carrying capacity, whereas welding of top flange, concrete compressive strength and extended bolts have limited effect on the mechanical characteristic of STS structure.The failure mode and mechanical characteristic of STS structure under three-point loading test were investigated, the main design parameters including spacing between the tubes, flange thickness, transverse connection mode and concrete compressive strength. The results showed that the STS structure exhibited a flexural failure mode under concentrated loading, and welding of bottom flange plate have a significant effect on the load-carrying capacity. The extended bolts, concrete compressive strength and welding of top flange plate have a limited effect on the mechanical characteristic of the STS structure. A low concrete compressive strength was able to improve the ductility of STS specimen and welding of top flange was helpful to increase the flexural capacity of STS structure.Based on the failure characteristic of STS structures, an analytical calculation formula was developed to predict the load-carrying capacity of STS structure under different transverse connection modes, and a good agreement between the test results and predicted values was obtained.According to the mechanical and failure characteristic of STS structure, a numerical simulation model was proposed to investigate the failure process and working mechanism of STS structure. The results of numerical simulation showed that the load-carrying capacity and flexural stiffness of STS structure increases with the increasing of tube thickness, and decreases with the decreasing of concrete content.The load-carrying capacity of STS structure with different ratio between flange plate thickness and tube thickness were investigated. The results indicate that the ratio ratio between flange plate thickness and tube thickness have effect on the failure patterns of STS structure, its reasonable region is the range of 1.0-1.3, which steel tube and flange plate were reached yield stress simultaneously under the ultimate capacity of the STS structure. Not only take full advantage of the two material strengths, but also can improve the ductility of STS structure. |
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