软垫层末端应力奇异性数值模拟

Numerical simulation on stress singularity at the end of soft cushion

本文采用非线性有限元中的接触模型,以龙滩水电站坝内压力钢管某设计方案为例,通过平面有限元数值模拟,全面分析设置软垫层后钢衬及混凝土的受力性态,研究软垫层末梢应力集中问题以及软垫层渐变段坡比、接触界面摩擦状态对混凝土环向局部应力峰值的影响。数值仿真结果表明:钢衬-混凝土接触界面存在的摩擦力对混凝土环向拉应力分布和峰值影响明显,较低的摩擦系数使界面接触压力分布趋于均匀,同时减少混凝土环向拉应力峰值。由于钢衬在软垫层末梢附近区域不能满足完全径向变形协调,钢衬-混凝土接触界面将出现局部微小张开区,形成软垫层末端应力奇异性;钢衬应力峰值应包括内水压力产生的膜应力与局部非协调变形产生的弯曲应力的叠加效应,设计恰当的软垫层渐变段坡比是减少钢衬和混凝土应力峰值的工程措施。

By using nonlinear FEM with 2D contact modeling, a case study of embedded penstock within dam and its around concrete of Longtan Hydropower Station in China is fully analyzed under the conditions of the designed cushion, the stress concentration at the end of cushion, the effect of slop ration, the influence of frictional status on contact interfaces between penstock and concrete and the peak annular stress within dam concrete. All the results by simulation computation show that the frictional force existed on the interface evidently influences on the peak values and the distribution of tension stresses around the hole of concrete, Lower frictional coefficient results in the uniform tendency of contact pressure distribution on the interface and as well as in decrease of annular tension stress around concrete. There exists a piece of opening segment on contact interface because of the incompatible radial deformation of penstock near the ending cushion, so there exists the stress singularity. Peak stresses of penstock may be considered as the superposition of both membrane stress produced by inner fluid pressure and bending stress induced by incompatible local deformation at the end of cushion. It will be effective to reduce the peak stresses both in penstock and in concrete by designing a suitable slop ratio at the end of cushion.