局部减薄压力管道极限分析的弹性模量缩减法

Elastic modulus reduction method for limit analysis of local wall-thinning penstock

为求解含局部减薄缺陷水电站压力管道的极限承载力,提出了该类管道极限分析的弹性模量缩减法。该方法定义了表征单元接近塑性屈服程度的无量纲参数—单元承载比,提出了动态识别局部减薄管道高承载区域阈值基准承载比的计算方法,建立了相应的弹性模量调整策略,可通过基于塑性极限分析原理的线弹性迭代求解含局部减薄压力管道的极限荷载。算例分析表明:本文方法具有良好的计算精度和适用性;21组缺陷结构的计算结果与弹塑性增量法(EPIA)误差均在8%以内;局部减薄轴向长度、深度和周向长度对极限荷载影响依次降低,减薄轴向长度无量纲参数A/R0t超过2.4将可能使极限内压降低45%以上。本文方法可为含缺陷管道结构极限分析和安全评估提供参考。

An elastic modulus reduction method （ EMRM） for the limit analysis of pressure pipes with local wall-thinning is put forward to estimate its ultimate loading capacity. The element bearing ratio （ EBR ） is defined as the dimensionless parameter to describe the degree of plastic yield of elements, and the reference EBR is defined as the threshold to dynamically identify the highly loaded areas of the pressure pipes with local wall-thinning. The related elastic modulus adjustment strategy was then proposed. The ultimate load of this pressure pipes can be determined using the linear elastic iterative analysis based on the plastic limit theory. Numerical examples are presented to demonstrate the applicability and accuracy of the proposed method. The limit loads of the pressure pipes with local wall-thinning given by the proposed method deviate by only 8 % from the results given by elasto-plastic incremental analysis （ EPIA ）. The influence of length , depth and width of defect on the limit internal pressure becomes weaker. And the limit internal pressure will be reduced by more than 45 % when the value of the non-dimensionalized parameter A/ R 0t is higher than 2. 4.The proposed method can provide reference for the limit analysis and safety evaluation of pressure pipes with local wall-thinning.