Seismic Analysis of Buried Jointed Pipes Considering Multi-node Excitations and Wave Propagation Phenomena

A study has been performed on the seismic analysis of jointed pipes systems in which the multi-node input and wave propagation in the body of the soil as well as the pipeline have been taken into consideration. For this purpose a computer program, prepared by C++ coding has been developed for 2D structures, which can take into account axial, flexural and shear deformations of the pipe segments. The program can also consider the soil-structure interaction by modeling the pipe surrounding soil as mass-damper-spring systems, which are supposed to be connected to the centerline of the pipe. It is also possible to introduce axial as well as rotational springs between the pipe segments to model the flexibility of the pipe joints. The efficiency and precision of the developed computer program have been shown by comparing its results with those of ANSYS computer program. Several cross-sectional properties of the pipe as well as various conditions of the surrounding soil have been used in analyses to find out the effect of different parameters on the seismic behavior of pipelines. At first the damping value for the pipeline material has been considered as zero, and then some other values have been used to find out how this property affects the seismic response of the pipeline. In addition to the effects of pipe and soil properties on the pipeline seismic response the effects of the pipe element's length in the precision of the response values have been studied. Numerical results show that the relative stiffness of soil with respect to the pipe has the most powerful effect on the pipe seismic response. In other words, for each given pipeline some special soil condition makes the pipe seismic response very extensive. These values are quite different, in some ranges of input frequencies, with those obtained by assuming infinite value for the shear wave velocity in pipe material, which is the implicit assumption in the usual seismic analyses. Therefore, to achieve a reliable and economic design, it is necessary to consider both multi-node excitation and wave propagation phenomena in the earthquake analysis of the pipeline systems.