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Validated 3D solid finite element (FE) models offer an accurate performance of buried pipelines at earthquake faults. However, it is common to use a beam–spring model for the design of buried pipelines, and all the design guidelines are fitted to this modeling approach. Therefore, this study has focused on (1) the improvement of modeling techniques in the beam–spring FE modeling approach for the reproduction of the realistic performance of buried pipelines, and (2) the determination of an appropriate damage criterion for buried pipelines in beam–spring FE models. For this paper, after the verification of FE models by pull-out and lateral sliding tests, buried pipeline performance was evaluated at a strike-slip fault crossing using nonlinear beam–spring FE models and nonlinear 3D solid FE models. Material nonlinearity, contact nonlinearity, and geometrical nonlinearity effects were considered in all analyses. Based on the results, pressure and shear forces caused by fault movement and pipeline deformation around the high curvature zone cause local confinement of the soil, and soil stiffness around the high curvature zone locally increases. This increases the soil–pipe interaction forces on pipelines in high curvature zones. The beam–spring models and design guidelines, because of the uniform assumption of the soil spring stiffness along the pipe, do not consider this phenomenon. Therefore, to prevent the underestimation of forces on the pipeline, it is recommended to consider local increases in soil spring stiffness around the high curvature zone in beam–spring models. Moreover, drastic increases in the strain responses of the pipeline in the beam–spring model is a good criterion for a damage evaluation of the pipeline.

This paper presents a novel nonlinear governing equation and solution procedure for analyzing a buried pipeline at an active strike‐slip fault crossing. The proposed method includes exact nonlinear axial and nonlinear transverse soil–pipe interaction terms, in addition to geometrical nonlinearity terms in the governing equation. The assumption of partitioning the pipeline into four segments with four governing equations based on the soil yield threshold is removed, and a unified governing equation is introduced. Compared with existing methods, the proposed method has a significantly extended application range with improved accuracy and provides the advantage of including the sliding of buried pipelines within soil, transverse soil spring plasticity, and improved large‐deformation effects including the sliding effect. The solution procedure is improved by removing the optimization steps and external calculations. The proposed method is verified by comparison to a verified finite element‐based model with various fault displacements and angles, and the results are in excellent quantitative and qualitative agreement with the numerical results, even for cases of large fault movement. Finally, criteria for assessing the ovalization damage of buried pipelines are proposed. The proposed method fulfills the missed part of literature, and it is valuable for (1) verification of the nonlinear FEM analysis; (2) fast, economic, and reliable stability analysis and design of buried pipelines; and (3) a strong tool for future developments of buried pipelines seismic design guidelines.

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