The Influence Of Initial Imperfections To Steel Structure Member

The stability capacity of simple support column under axial compression and the bending beam can get the analytical solution through theoretical analysis. But there is no analytical solution when taking into account of the initial imperfections and material nonlinear. As initial bending, load eccentricity and residual stress are existed in the steel member and some points on the cross section may yield after buckling, it is necessary to use nonlinear analysis method to track the response of the structure under load and the ultimate bearing capacity of the structure is obtained.Specification for the initial imperfections of steel member is based on theoretical derivation and experimental data. Then, the numerical calculation fitting results are used to form formula for calculating the stability capacity of bending beam, axial pressure column and beam column. This paper uses a co-rotational 9-node quadrilateral elasto-plastic shell element for the nonlinear analysis of steel member. Initial flexure and load eccentricity are merged into an initial flexure. The residual stress part is adopted in energy equation and the material nonlinear model is derived.Through several examples, it is found that the bending beam, axial pressure column and beam columns is sensitive to initial flexure with a different ultimate bearing force in the range of fifteen percent. The reduction caused by residual stress towards bending beam is up to eight percent, while that of axial compression column is four percent and that of beam column is six percent. The higher peak value of residual stress is, the lower the bearing capacity is, and the influence of the residual stress is related to the slenderness ratio and load form.In addition, the results are compared with specification results. It shows that the formula of specification is safe; the load-displacement curve of nonlinear analysis is compared with ANSYS, and the maximum deviation is about four percent.