AN IMPROVED ANALYTICAL STRAIN ANALYSIS METHOD FOR BURIED STEEL PIPELINES SUBJECTED TO ABRUPT PERMANENT GROUND DISPLACEMENT

摘要

Abrupt permanent ground displacement is a typical loading condition for pipelines crossing geotechnical hazard areas. An improved analytical method for calculating longitudinal strain of buried pipeline under tension combined with bending load induced by permanent ground displacement (PGD) was proposed, in which, the pipe steel was considered as a bilinear material and the soil constraint on pipe was considered as a series of elastic-plastic nonlinear soil springs. Effects of elastic deformation of axial soil springs on pipe strain was derived accurately. Effects of axial force in pipe on pipe's bending deformation was considered directly in the governing equation of pipe. Equilibrium between the section stresses in the large deformed pipe sections near fault trace and the section force and moment at the same position derived by the beam theory was used to obtain the nonlinear stress distributions in the pipe section and furtherly to obtain the equivalent modulus describing the locally decreased pipe stiffness. This method makes it possible to accurately derive the pipe longitudinal strain considering the effects of pipe material nonlinearity induced locally decreased pipe stiffness in large bending deformed pipe segments. A three dimensional nonlinear finite element model was also established by general software package ABAQUS to serve as a benchmark to validate the accuracy of proposed analytical method. Shell and pipe elements were employed to simulate pipes in large deformation and small deformation regions respectively. Distributed nonlinear soil spring elements were employed to simulate nonlinear soil constraints on pipe. Various loading conditions were performed to compare the efficiency and accuracy of the proposed analytical method comparing with the FE method. Results show the proposed analytical method can predict accurate longitudinal strain results even large plastic deformation appears in pipe. And comparing with FE method, analytical method has advantages in calculating efficiency, which is more suitable for application in engineering practice.