强风作用下超大型冷却塔结构失效准则与强健性分析

Structural failure criterion and robustness analysis of super-large cooling towers subjected to strong winds

为分析超大型冷却塔在强风作用下的结构失效准则与强健性,以超规范高度限值的世界最高220 m超大型冷却塔为例,基于ANSYS/LS⁃DYNA平台建立结构三维有限元模型,对其风致倒塌全过程进行数值仿真分析。研究了典型风速下位移响应与塔筒内力分布特性,得出最不利响应发生的位置、数值及分布规律,探讨了强风下塔筒结构“稳定⁃失稳⁃倒塌”全过程演化机理,并提出了强风作用下冷却塔的结构失效准则。研究发现:强风作用下超大型冷却塔结构强健性最薄弱部位为迎风面塔筒喉部区域,与上风向夹角为−70°和70°子午向出现“褶皱变形”并导致塔顶局部结构失效破坏,进而引起塔筒整体结构倾覆倒塌;塔筒应变能密度呈现指数增长趋势,以喉部相对水平位移与喉部直径百分比S>1%、指数应变能密度和值破坏系数K≥0.3作为结构失效判断准则可较好评价强健性指标。

Wind load is the control load in the design of large cooling tower structure,and the current wind-resistant guiding ideology is based on strength design theory. However,several wind-damaged events in history indicate that excessive local wind load may also lead to local tension damage of the tower tube,which leads to progressive collapse and buckling instability of the whole tower tube structure. The structural damage caused by local wind-induced damage is a typical form of structural robustness damage,and this kind of problem has become a new challenge for the development of cooling towers. In order to analyze the structural failure criteria and robustness of super-large cooling towers subjected to strong winds,a three-dimensional finite element model of super-large cooling towers with the highest height limit of 220 m in the world is established based on ANSYS/LS-DYNA platform and the whole process of wind-induced collapse is simulated. The displacement response and the internal force distribution of the cooling tower under typical wind speed are studied,and the location,numerical value and distribution rule of the most unfavorable response are extracted.The whole process evolution mechanism of "stability-instability-collapse" of the cooling tower under strong wind is discussed,and the structural failure criterion of the cooling tower under strong wind is put forward. It is found that the weak position of structural robustness of super-large cooling towers under strong wind is the throat area of the tower tube on the windward side,where "fold deformation" occurs in the meridional direction of-70° and 70°,leading to the failure of the local structure on the top of the tower and the collapse of the overall structure of the tower tube. The strain energy density of the tower tube shows an exponential trend. The percentage of the relative horizontal displacement of the throat to throat diameter S>1%,failure coefficient of exponential strain energy density K≥0.3 can be used as the criterion for judging structural failure,and the robustness index can be well evaluated.