Distortional Buckling Of Cold-formed Thin-walled Lipped Beams

Cold-formed steel are widely used in industrial and civil construction for many advantages, such as light weight, good section properties, easy installation, etc., As an important strength-governing mode, distortion buckling has been received more and more attentions in recent years.This dissertation take a deep study on distortional buckling of cold-foremed lipped members.Firstly, focused on cold-formed lipped C-section member under strong axised-moment, an approximate analytical solution of the rotational restraint provided by web is estimated by Galerkin method. Based on an existing theoretical solution in conjunction with numerical results obtained using the Generalised Beam Theory (GBT). a simplified equation is finally presented to predict the elastic distortional buckling load of cold-formed lipped C-section member subjected to major axis bending, whose accuracy is then confirmed by comparison with the existing theory.Next, the finite element software ABAQUS is applied for elastic and elastic-plastic analysis of cold-formed lipped C-section member. A detailed parametric analysis using elastic buckling is carried out on the inclined lipped sections, mainly focused on distortional buckling coefficient due to the length of beam and the angel of lipped flange. The value of influence coefficients are given, which expand the applicability of the simplified formulas raised in the previous chapter. Studies on the elastic-plastic buckling load and ultimate load capacity, especially on the effects of initial imperfection are made through FEM.elastic-plastic nonlinear analysis.And then quantitative analysis is carried out on effect of the reinforcing measures (such as connected-bars, connected-slabs and connected- diagonals etc). FEM elastic analysis are conducted on strengthened sections with various reinforcement spacing . formulas of the load enhancing factor of the three kinds of reinforcement measures are put forward through the parameter analysis. Subsequent elastic-plastic analysis on reinforcement effect are conducted . and the validity of the reinforcement methods is further validated. The best reinforcement measure is proposed based on both reinforcement effect and steel amount. Finally, the simple formulae for the elastic distortional buckling load of cold-formed lipped C-section member is extended to the Z-section member, with the relevant parameters modified and derivated , the simplified formula for calculating buckling loads of Z-shaped section bending distortion is then presented . ABAQUS analysis are conducted on the effect of load due to the length of beam and the angel of lipped flange. Buckling loads are found to be very close between the C and Z-section member with the same section size.