FORMULATION AND IMPLEMENTATION OF THREE-DIMENSIONAL DOUBLY SYMMETRIC BEAM FINITE ELEMENTS WITH WARPING EFFECTS IN OPENSEES

摘要

This paper incorporates warping effects of doubly symmetric beam-column elements into OpenSees. OpenSees is an object-oriented, open source software package for non-linear finite element analysis. A key feature of OpenSees is the ability to integrate existing libraries and new elements into the framework without the need to change the existing code. The non-linear beam-column element theory in OpenSees is based on the assumption that torsion is uniform along the length of the member and nonuniform warping torsion is excluded. In this paper, the OpenSees source code is modified and a corotational mapping for three-dimensional analyses of doubly symmetric beam-column elements is incorporated to take account of warping effects. Both a local linear strain assumption and a second order approximation of the Green-Lagrange strains are considered in the formulations of the beam-column elements at local level. Numerical examples are presented to demonstrate the accuracy of the proposed elements by comparisons with results from the literature. Good agreement is achieved for both ultimate loads and load-deflection curves.