Features of analysis of main pipelines seismic resistance

The problems of stress analysis in main underground pipelines under seismic action are considered. It is shown that the bending stresses arising in the pipeline during the passage of a seismic wave are small and should not entail dangerous consequences for it (except for areas with high local stresses: surroundings of defects, bends, T-pipe). A significant danger is represented by large soil movements, which can occur in zones of tectonic faults. In these cases, the soil displacement can be estimated at meters, which should lead to high stresses. To analyze the stresses arising in a pipe in a soil movement zone, the finite element method implemented in the LS-DYNA program was used. It is shown that taking large deformations into account when using Lagrange's formulation requires the exclusion of some of the elements from the model during the calculation and leads to errors that do not go to the safety factor. The combined approach (the Lagrange approach for a pipe whose deformations are not too large and the Euler approach for the soil) is free of this shortcoming and provides an opportunity to analyze the consequences of large soil displacements. A fully parameterized model is developed that allows to make calculations on comparison of the effectiveness of various measures with a minimum labor input from the developer: changes in the profile of the trench (which is particularly important for horizontal displacements), properties and thickness of the backfill layer, properties and wall thickness of the pipe material. As one of the non-standard methods to ensure safety, the use of pipes with ribs is considered.