水体-结构-地基耦联的泵站出水塔地震响应分析

Seismic response analysis of outlet tower based on water-structurefoundation coupling system

泵站出水塔是一种连接泵站压力管道和下游输水渡槽的塔式结构,为保证结构安全运行,有必要对其进行地震响应分析。该文以景泰川二期六泵站出水塔为研究对象,考虑流固耦合效应,依据弹性波理论,建立出水塔结构无质量地基模型和粘弹性边界模型,进行出水塔体系有无水体2种工况下的研究,根据泵站出水塔现场实测数据,提取结构的固有工作频率,并与流固耦合模型干湿模态结果进行对比分析,验证所建流固耦合模型的合理性及流体对出水塔体系的影响。分别对无质量地基模型与粘弹性边界模型进行地震波输入,对比分析相应的动力响应,探讨水体-结构-地基耦联系统相互作用的影响规律。研究表明:出水塔结构工作基频为3.3 Hz;结构内水体降低出水塔的固有频率,增加出水塔的地震响应,在进行地震计算分析时,不应忽略;粘弹性边界模型在地震计算中能够考虑辐射阻尼效应,与无质量地基模型计算结果相比,出水塔特征点的位移响应最大值降低38.5%,应力幅值降低37.8%,因此地基建议选用粘弹性边界。研究成果可为后续出水塔结构模态辨识及地震分析提供理论指导。

Outlet tower of pumping station is a tower structure connected to the pumping station pressure pipes and downstream aqueduct. In order to ensure the safe operation of the structure, it is necessary to analyze its seismic response. Taking second stage sixth pumping station outlet tower of Jingtaichuan project as the research object, the large FEM software ANSYS was used to establish the massless foundation model and the viscoelastic boundary model of outlet tower based on fluid-solid coupling effect and elastic wave theory. First, combining the efficient and accurate modal calculation method, the modal analysis of the water tower system under 2 conditions of with water or not was carried out. The measured datas of the outlet tower was treated by the shock-resistant DP seismic low frequency vibration transducer. Furthermore, the CEEMDAN-SVD method proposed by author was used to filter strong background noise and extract the vibration feature information of each measuring point of the structure. The information fusion method of variance contribution rate was used to dynamically fuse the signal after denoising of measuring points, and the complete work feature information of the water tower was obtained. Then, the natural vabration frquency of the water tower structure was extracted and the vabration frquency was compared with the dry and wet modals of the fluid-solid coupling model. The rationality of the established fluid-structure coupling model and the effect of the aqueous medium on the natural vibration characteristics of the outlet tower system were verified. Subsequently, based on the identification and modal analysis conclusions, according to the location of the project, the Lanzhou wave was selected as the seismic input time-history of the dynamic response analysis. The three-way seismic wave time-histories were inputted simultaneously to both the massless foundation model and the viscoelastic boundary model under the conditions of with water or not. The results of the relative displacement time-history and the maximum value of tension-compression stress of node A under 2 operating conditions was compared, and the influence of the interaction among the water-structure-foundation coupling system was analysied. The results showed that, comparing dry and wet modal calculation results with CEEMDAN-SVD identification results, it can be seen that the working frequency of the outlet tower is 3.3 Hz, and the water reduces the modal frequency of the tower. Through the analysis of the displacement and stress responses, it can be seen that the condition 1 is an unfavorable working condition. Compared with the results of the massless foundation, the displacement response value of the viscoelastic boundary results is reduced by 38.5% and its stress response value is reduced by 37.8%. The maximum displacement response of the condition 2 is 63.8% which is lower than that of condition 1, and the maximum stress response reduces by 73.1%. In the models of this paper, the effects of water and viscoelastic boundary on the seismicity of the outlet tower are opposite. When the water and viscoelastic boundary were considered at the same time, the seismic displacement and stress response results under the condition of massless foundation with waterless are smaller than those of with viscoelastic boundary and water condition. These results indicated that the water body has greater impact on the seismicity of water tower and is more important. The water increases the seismic response during the calculation of seismic response of water tower, and it should not be neglected. For the selection of foundation conditions to calculate the seismic response of water tower, the massless foundation is safer, and the viscoelastic boundary foundation which considering the infinite foundation radiation damping is recommended.