A comparative study between displacement and mixed-based corotational finite element formulations for elasto-plastic analysis of three-dimensional beams

International audiencePurpose - The purpose of this paper is to present eight local elasto-plastic beam element formulations incorporated into the corotational framework for two-noded three-dimensional beams. These formulations capture the warping torsional effects of open cross-sections and are suitable for the analysis of the nonlinear buckling and post-buckling of thin-walled frames with generic cross-sections. The paper highlights the similarities and discrepancies between the different local element formulations. The primary goal of this study is to compare all the local element formulations in terms of accuracy, efficiency and CPU-running time. Design/methodology/approach - The definition of the corotational framework for a two-noded three-dimensional beam element is presented, based upon the works of Battini .The definitions of the local element kinematics and displacements shape functions are developed based on both Timoshenko and Bernoulli assumptions, and considering low-order as well as higher-order terms in the second-order approximation of the Green-Lagrange strains. Element forces interpolations and generalized stress resultant vectors are then presented for both mixed-based Timoshenko and Bernoulli formulations. Subsequently, the local internal force vector and tangent stiffness matrix are derived using the principle of virtual work for displacement-based elements and the two-field Hellinger-Reissner assumed stress variational principle for mixed-based formulations, respectively. A full comparison and assessment of the different local element models are performed by means of several numerical examples. Findings - In this study, it is shown that the higher order elements are more accurate than the low-order ones, and that the use of the higher order mixed-based Bernoulli element seems to require the least number of FEs to accurately model the structural behavior, and therefore allows some reduction of the CPU time compared to the other converged solutions; where a larger number of elements are needed to efficiently discretize the structure. Originality/value - The paper reports computation times for each model in order to assess their relative efficiency. The effect of the numbers of Gauss points along the element length and within the cross-section are also investigated