沉管隧道地震反应分析局部精细化建模中的几个问题

通过大型沉管隧道的实例分析和前期研究成果,重点讨论沉管隧道地震反应分析中建立局部三维精细化模型时所应关注的4个问题:1模型范围大小的问题;2上覆水体动水作用的简化;3时域分析中阻尼矩阵的合理建模及其影响;4地震输入方式的选择与影响等。文中通过工程算例验证局部三维精细化建模的合理方式,研究结果表明:考察某段沉管管节的地震反应时,应至少考虑该管节两端各三段相邻管节的影响和轴向5倍以上土层厚度范围的土层影响;上覆水体可近似采用等效附加质量的方式模拟;当沉管隧道-土层体系的基频低于输入地震波的卓越频率时,易采用基于体系基频的优化方法来确定Rayleigh比例阻尼矩阵的比例系数;沿沉管隧道轴向的多点地震输入对隧道地震反应有较大影响,应加以充分关注。

Several problems in refined local modeling for seismic response analysis of immersed tunnel

Based on the case study of a large-scale immersed tunnel and the previous research results, several problems in establishing the refined local model for seismic response analysis of the immersed tunnel are discussed emphatically as follows: (1) problem of model range size, (2) simplified method for hydrodynamic action of overlying water body, (3) the proper model of damping matrix in time domain and its effect, (4) selection of seismic input mode and its effect. The reasonable way for three-dimensional refined local modeling of the immersed tunnel is verified by engineering examples. The numerical results show that when the seismic responses of an immersed tunnel pipe is investigated carefully, at least the influence of other three pipes at two sides of the pipe must be considered and the effect of the limited soil layer whose horizontal length is at least 5 times the thickness of the soil layer at two sides of the pipe should be included. The method of equivalent additional mass can be used to simulate the overlying water body. When the fundamental frequency of the immersed tunnel-soil layer system is lower than the predominate frequencies of the input seismic wave, the ratio coefficients of the Rayleigh proportional damping matrix are determined by the optimization method based on the fundamental frequency of the system. It should be fully noted that the excitation of multi-support seismic input along tunnel axis has a great influence on the seismic response of the immersed tunnel.