NONLINEAR-ANALYSIS OF THIN-WALLED MEMBERS UNDER BIAXIAL BENDING

A numerical method for the nonlinear and instability analysis of thin- walled members (NISAT) subjected to biaxial bending has been developed which includes the warping degree of freedom at each node. The analys is includes the effects of geometric nonlinearity, out-of-plane bendin g and the consequent torsion, secondary effects of load applied away f rom the shear centre, large displacements and rotations in the three-d imensional space and initial imperfections. The effects of large displ acements is included in the nonlinear analysis following the updated L agrangian method where the nodal coordinates are updated before every load increment. The analysis does not consider distortion of the cross -section. The nonlinear biaxial bending behaviour of thin-walled Z- an d sigma sections subjected to transverse load is studied analytically using the NISAT program and the results are compared with experimental values. The failure load, midspan displacements and the normal stress es at critical points of the midspan section are also compared.