Study on Shear Design of Underground Concrete Structures

虽然到目前为止已经建造了许多地下混凝土结构，但这种结构的设计是基于对地球上结构的研究成果。然而，人们认为，在土压力作用下，地下结构比集中荷载作用下的地下结构具有更有利的性能。由于地下结构一般由平面构件组成，因此希望在没有剪切配筋的情况下能够获得所需的强度和延性。此外，在结构的极限状态下，可以预期地球的约束作用。本研究的目的是建立合理的地下混凝土结构抗剪设计方法。为达到这一目的，本文进行了钢筋混凝土受弯节点梁和钢筋混凝土板的试验研究。1)钢筋混凝土受弯构件的剪切破坏模式可分为三种类型：(A)单斜裂缝斜拉破坏，(B)双斜裂缝斜拉破坏，(C)混凝土在连接载荷点和支撑点方向的受压破坏。2)破坏模式(A)的极限强度可以用相应的剪跨来计算。3)模式(B)的极限强度可以用接近对弯点的每个剪跨的计算值中的较大者来计算。4)收缩弯曲点对模式(C)的极限强度影响不大。5)具有反弯点的构件在分布荷载或多重荷载作用下的极限强度可以根据剪力各分量的累积损伤来计算。6)受剪钢筋在平面构件中的作用随钢筋布置的不同而不同。

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.