3-D finite element analysis of underground water pipelines under non-uniform seismic excitation

It's well known that the seismic numerical analysis of most buildings use the uniform excitation due to the small geometrical dimensions compared to the wavelength of seismic waves. That means the earthquake ground motion exerted on the simulation model is essentially represented by one point excitation. However, because of the large geometrical dimensions of pipelines and seismic wave propagation effects, the prior assumption is not valid. Different points along the pipeline axis are subjected to different seismic excitations including the change of wave shape, ground motion phase and so on. The dynamic response of the water pipelines to seismic excitation is influenced by many factors, both of the ground conditions, for example the complex ground strata and soil's dynamic constitutive model, and the structural mechanical behaviors, like the concrete's dynamic constitutive model and complex geometrical dimensions of the pipelines. So the 3-D finite element analysis of water pipelines is very complicated because of the complex geometrical shapes, ground conditions and the constitute models. In order to simply the research question we make some assumptions, which includes the fluid(water) here is just considered as a load exerted inside the tunnel linings and the soil liquefaction problem is beyond the scope of this paper. As a matter of fact, the structure of water pipelines is the focus of this paper. A study of underground pipelines subjected to non-uniform seismic excitation using shaking table tests was reported by Meng (2008). The data of the shaking table tests clearly show that when the pipelines is subjected to the non-uniform seismic excitation, its dynamic response is different with the one under uniform excitation and some parts' response is more severe. It can be seen that it is more realistic and worthy that the non- uniform seismic excitation should be considered in the analysis of the seismic responses of the pipelines.