Study on Shear Design of Underground Concrete Structures

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Although many underground concrete structures have been constructed till now, the design of such structures was based on the results of research on the structures on earth. However, it is considered that the underground structures subjected to distributed loads due to earth pressure have more profitable property than the structures with concentrated loads. As the underground structures generally consist of plane members, it is desired that the required strength and ductility will be obtained without shear reinforcement. Furthermore, restraint action of the earth may be expected at the ultimate limit state of the structures. The purpose of this study was to establish reasonable design method for shear of underground concrete structures. To achieve this purpose experiments of reinforced concrete beams with contraflexure point and reinforced concrete slabs were made.The principal results obtained in this study are as follows. 1)Modes of shear failure of reinforced concrete members with contraflexure point can be classified into three types ; (a)diagonal tension failure by a single diagonal crack, (b)diagonal tension failure by two diagonal cracks, and(c)compression failure of concrete in the direction connecting load point and support point. 2)Ultimate strength for failure mode(a)can be calculated by using corresponding shear span. 3)Ultimate strength for mode(b)can be calculated as the larger of the calculated values for each shear span bordering contraflexure point. 4)Contraflexure point has little effect on the ultimate strength for mode(c). 5)Ultimate strength of the member with contraflexure point subjected to distributed or multiple loads can be calculated on the basis of the cumulative damage by each component of shearing forces. 6)The effect of shear reinforcement in plane members varies with the arrangement of the reinforcement.