Analytical Model Versus Numerical Model in Stress-Strain Analysis of Buried Steel Pipelines Subjected to Fault Displacements

Abstract eng:
In the present paper the results of the analytical model for a nonlinear stress-strain analysis of buried steel pipelines at active fault crossings are analyzed and discussed versus the numerical finite element results. The analytical model is based on the partition of the pipeline into four segments. The two segments in high curvature zones on both sides of the fault are modeled as beams in bending and tension with direct account for the axial force in the equations of motion. The two other segments are treated as beams-on-elastic foundation. The interaction of the pipeline with the surrounding soil is taken into account in axial and transverse directions using bilinear soil diagrams. The nonlinearity of the pipe steel is introduced on a cross-section level assuming a bilinear stress-strain relationship. The analysis is performed iteratively as a series of elastic solutions using a secant modulus of the pipe steel. The analysis of applicability of the proposed model to various cases of pipeline-fault intersection conditions is performed through the comparison of the results obtained with the analytical model to the results of the numerical simulation of the finite element model in ANSYS. The developed finite element model uses current technology ANSYS pipe elements with account for axial, bending, shear and torsional deformations, material nonlinearity, large displacements and strain nonlinearities. The pipe-soil interaction is modeled by the nonlinear soil spring elements. The analysis of the results allows drawing the conclusion on the applicability of the proposed analytical methodology to a wide range of conditions met in practice, at least for the preliminary assessment. The limitations of the analytical methodology and possible further refinements are also discussed.

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