Elasto-plastic finite element for pipelines.

Abstract

An efficient pipe element for the modeling of the inelastic behaviour of three-dimensional pipes is presented. The formulation is based on a two-node element with twelve degrees of freedom. The element consists of an elastic portion and two potentially plastic generalized 3D hinges located at both nodes. The formulation is based on a lumped plasticity approach. The behaviour of plastic hinges is characterized using recently developed interaction relations for pipe sections. The interaction relations are exact and include the effects of axial force, bi-axial bending moments, bi-axial shear, torsion and internal and/or external pressure. The element models shear deformation effects both in the elastic and plastic ranges. Therefore, it is suitable for predicting the behaviour of pipe segments subject to high shear forces. The analysis is implemented using the displacement control scheme in order to capture the peak point of the load deformation response without numerical difficulty. The normality condition concept in conjunction with the yield hyper-surface at stress resultant level is used to approximately simulate the material nonlinearity effects. The developed technique models material nonlinearity in a very efficient way when compared to full 3D or shell finite element analysis. The model is thus particularly suitable for long pipeline systems. Solutions for simple problems are provided and compared to several other well-established elements in the ABAQUS(TM) library in order to assess the validity of the results and demonstrate their scope of applicability. A discussion of additional features that can be added to the analysis is also presented.