大型高耸钢筋混凝土冷却塔属于典型的风敏感型结构，近年来在地震、飞机撞击、爆破等极端外部作用下动力响应研究也得到了工程界的广泛关注。土－结构动力相互作用效应（Soil Structure Interaction，SSI）对于大坝、桥梁等类型工程结构地震响应的影响研究成果较为丰富，而对冷却塔结构体系的影响程度方面很少涉及。依据弹性波动理论结合有限单元法，建立和推导了考虑土－结构动力相互作用的三维黏弹性人工边界模型和公式，并通过半空间自由场模型验证该地震动输入方法的准确性。以国内实际工程项目———某火电厂大型冷却塔为研究背景，以通用有限元程序 AN-SYS 为平台，分别建立了冷却塔刚性地基模型、无质量地基模型和黏弹性人工边界模型，开展模态分析及弹性时程分析，研究不同计算模型相应的动力特性及内力变化，探讨了土－结构动力相互作用的影响规律。研究结果表明：考虑刚性地基，冷却塔结构体系自振频率分布十分密集，绝大多数振型为环向谐波和子午向谐波组合的局部振型；考虑弹性地基后，结构的自振频率略有降低，整体振型较早出现。通过时程分析可知，采用黏弹性人工边界模型，考虑无限地基辐射阻尼效应，与刚性地基模型相比，塔筒的绝对加速度最大值降低43．4％，塔筒沿子午向弯矩轴力幅值降低约50％，而环向内力却均显著提高，X 支柱内力幅值降低约20％~50％．因此，在进行冷却塔地震响应分析时，土－结构动力相互作用的影响不可忽视。%A large-scale high-rise reinforced concrete cooling tower belongs to a typical wind-sensitive structure.In recent years,its dynamic response study under extreme external actions,such as,earthquake,jet-crash,blasting et.al receives extensive attention in engineering field.The study achienements about the effects of soil-structure interaction (SSI)on seismic responses of dams and bridges are relatively abundant,however,they are seldom involved in cooling towers.Here,based on the elastic wave motion theory combined with the finite element method,a 3D visco-elastic artificial boundary model and its formulas were built and deduced considering soil-structure dynamic interaction,and the correctness of the earthquake input method was verified with the half space free field model.A large cooling tower in a certain coal-fired power plant,one of the domestic engineering projects was taken as a study background,based on the FE software ANSYS,the cooling tower's rigid foundation model,its massless foundation model and its viscoelastic artificial boundary model were modeled,respectively.The modal analysis and the elastic time history analysis were performed in order to study dynamic characteristics and changes of internal force of these models.The influence laws of soil-structure dynamic interaction on different models were explored.The research results showed that the cooling tower structure system natural vibration frequency distribution considering rigid foundation is very dense,and the majority of vibration modes are local coupling vibration modes in ring and meridian directions;the natural vibration frequencies are slightly reduced considering elastic foundation,and the whole body vibration modes appear earlier;with the time history analysis,using the visco elastic artificial boundary model,considering the infinite foundation radiation damping effect,compared with the rigid foundation model,the maximum absolute acceleration of the tower tube reduces 43.4%,the moment and axial force in meridian direction reduce 50%,and they in ring direction increase significantly;internal force amplitude values of X column reduce about 20%~50%;therefore,when performing the seismic response analysis of the cooling tower,the influences of soil-structure interaction can not be neglected.
展开▼
