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粘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ANSYS为平台，分别建立了冷却塔刚性地基模型、无质量地基模型和粘弹性人工边界模型，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，采用粘弹性人工边界模型，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。
Abstract
Large-scale high-rise reinforced concrete cooling tower belongs to typical wind-sensitive structure. In recent years, study on dynamic response under extreme external actions, such as earthquake, jet-crash, blasting et. al gets extensive concern in engineering field. Research on earthquake response influence for projects like dams, bridges and so on taking into account soil structure dynamic interaction is relatively abundant, however it is seldom involved in cooling tower. Based on elastic wave motion theory combined with finite element method, 3D viscous-spring artificial boundary model and formula were set up and deduced while considering soil structure dynamic interaction, and verify the accuracy of the earthquake input method through half space free field model. A large cooling tower in coal-fired power plant in domestic engineering project as the research background, based on general program ANSYS platform, cooling tower rigid foundation model, massless foundation model and viscoelastic artificial boundary model were modeled respectively. Modal analysis and elastic time history analysis were performed in order to study dynamic characteristics and changes of internal force, influence law of soil structure dynamic interaction for the different model was discussed. Research results show that the cooling tower structure system natural vibration frequency distribution is very dense, and the vast majority of vibration modes are local coupling vibration mode in ring and meridian directions. The natural vibration frequencies are reduced due to considering elastic foundation, and the whole vibration mode appear earlier. Through time history analysis it can be seen that by using the viscous-spring artificial boundary model, considering the infinite foundation radiation damping effect, compared with the rigid foundation model, the maximum absolute acceleration of tower reduces to 43.4%. Moment and axial force in meridian direction reduces 50%, and in ring direction increases significantly. Internal force amplitude value for X columns reduces about 20%~50%. Therefore, when performed the earthquake response analysis of cooling tower, it cannot be neglected influence of soil structure interaction.
关键词
冷却塔结构 /
地震响应分析 /
土-结构动力相互作用 /
粘弹性人工边界 /
自由场分析 /
地震动输入
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Key words
Cooling tower structure /
Earthquake response analysis /
Soil structure dynamic interaction /
Viscous-spring artificial boundary /
Free field analysis /
Earthquake input
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