Study on Shear Design of Underground Concrete Structures

虽然迄今为止已经建造了许多地下混凝土结构，但这些结构的设计都是基于对地面结构的研究成果。但一般认为，地下结构在土压力作用下承受分布荷载比承受集中荷载更有利。由于地下结构通常由平面构件组成，因此希望在没有抗剪钢筋的情况下获得所需的强度和延性。此外，在结构的极限状态下，可以预期土的约束作用。本研究旨在建立合理的地下混凝土结构抗剪设计方法。为实现这一目的，进行了钢筋混凝土反弯点梁和钢筋混凝土板的试验研究。1)钢筋混凝土反弯点构件的剪切破坏模式可分为三种：（a）单斜裂缝斜拉破坏，（B）双斜裂缝斜拉破坏，（c）荷载点与支承点连接方向的混凝土受压破坏。2)破坏模式（a）的极限强度可通过相应的剪跨计算。3)模式（B）的极限强度可以计算为反弯点边界的每个剪跨的计算值中的较大值。4)反弯点对模式（c）的极限强度影响不大。5)具有反弯点的构件在均布荷载或多重荷载作用下的极限承载力可按各剪力分量的累积损伤计算。6)平面构件中抗剪钢筋的作用随钢筋布置方式的不同而不同。

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.