Dynamic Response of Continuous Buried Pipes in Seismic Areas

Although seismic events rarely cause structural damages to buried pipelines, they can neverthless result in a significant loss of functionality. While the dynamic response of a pipe is obviously dependent on the characteristics of the seismic event and the type of pipe in question, a careful assessment of the stresses induced by the earthquake cannot neglect the interaction between the pipeline and the surroundig soil. In the present paper a numerical model is developed in order to evaluate the dynamic stresses acting on buried pipes under the hypothesis that the soil is a Winkler elastic medium and the pipe can be held to be continuous thanks to the welded joints employed. The model allows to evaluate the influence of the pipe length and the type of constraining conditions at the ends of the pipe into the assessment of earthquake effects. In particular, it was decided to refer to the conditions both of the end-free pipe and the end-constrained pipe, so as to better highlight the influence that the end constraints have on pipe displacements. The model makes it possible to evaluate, with reference to specific boundary conditions and at a generic abscissa, the trend over time of the pipe’s axial and transverse displacements. These can then be used to define the corresponding trends over time of the deformations and, hence, the stresses acting on the pipe. In this note the pipe-soil interaction model is discussed. Then, with reference to steel and HDPE pipes with welded joints, a numerical analysis is conducted, showing from a technical standpoint that once the characteristics of the seismic wave, of the soil and of the pipe have been assigned, the pipe’s dynamic response is also strongly affected by pipe length and the type of constraints.