ABSTRACT
Beam finite elements based on the Generalized Beam Theory (GBT) are presented, in which the cross-section displacement field is constructed via linear combinations of GBT cross-section deformation modes so that the local deformations, such as cross-section distortion, local buckling and out of plane warping, can be involved. The proposed model involves both the material (e.g. thermal softening effects of steels) and geometrical nonlinearities (e.g. large deflections). It can be used to investigate thin-walled steel members under arbitrary temperature distributions. A kind of bilinear temperature dependent stress-strain relationship for carbon steels proposed by Lie (1992) is used in present model. To trace the post-collapse paths of steel columns in fire, a viscous damping based dynamic relaxation method is used to solve the nonlinear balance equations. A set of fire tests on steel elliptical tubular columns are investigated, where the comparison of results shows high accuracy and validity of the present beam finite elements. Moreover, the superiority of the present model lies in its ‘structural clarity’, because its modal solutions can give an insight into the collapse mechanism of thin-walled steel members in fire.
