GEOMETRIC NONLINEAR ANALYSIS OF STEEL FRAMES CONSIDERING INITIAL IMPERFECTION AND WARPING DEFORMATION

摘要

To realize accurate structural analysis, based on the theory of continuous medium mechanics and updated Lagrangian formation, a new geometric nonlinear analysis method which can be used to describe even wider range of space steel frames is presented. The stability interpolation functions which are derived from the fourth-order differential equations of the beam-column are adopted to derive second-order elastic stiffness matrix of 3-D beam-column element. In die derivation, torsion-warping interpolation functions are used to consider the warping deformation. With some modifications, die member bowing effect and initial out-of-straightness are also considered. The element can be used to predict accurately the lateral displacement under the effect of axial forces, and the buckling loads due to the axial-torsional and lateral-torsional instabilities. And the proposed approach allows nonlinear behavior of spatial frames to be captured with fewer elements per physical member. Numerical examples are presented and the results show the new matrix is accurate and suitable for the geometric nonlinear analysis of steel frameworks.