Distortional Buckling Of Cold-formed Thin-walled Lipped Channel Members’Capacity

Distortional buckling which is one of the most important buckling modes for cold-formed lipped channel sections as well as local buckling and global buckling may change mechanical properties and decrease the ultimate load of members. Nowadays however it is the key factor of bearing capacity of many components for higher yield strength of material, thinner panel, more complex cross section shape. This dissertation takes a deep study on distortional buckling of cold-formed lipped members.Firstly, this paper reviews research achievements in distortional buckling, compares the existed design methods for bearing capacity of axial compression and bending according to five national (regional) codes and the latest research achievements. Based on the comparison between five calculating data and test results for capacity under axial compression of cold-formed thin-walled lipped channel members, it is shown that the design method of North American specification has widespread application and relatively high accuracy, which could supply references for structural design.Next, focused on cold-formed lipped channel members (RA and RL) under strong axised-moment, deep and total analysis has been taken, including the rotational restraint, critical half wave length, corrected parameter. Then a simplified equation is finally presented to predict the elastic distortional buckling load of cold-formed lipped channel member (RA and RL) subjected to major axis bending, whose accuracy is then confirmed by comparision with CUFSM.And then focused on cold-formed lipped channel member under strong axised-moment and axial compression, an approximate analytical solution of the rotational restraint provided by web is estimated by Galerkin method. And then the accuracy is confirmed by comparison with finite element method. At last, a simplified equation is present between the rotational restraint and the stress of the web.Finally, FEM elastic analysis is carried out on effect of the reinforcing measures (such as connected-bars, connected-slabs and connected-diagonals etc) under minor axised-moment and axial compression. Analysis are conducted on strengthened sections with various reinforcement spacing and the parameter analysis. The best reinforcement measure is proposed based on both reinforcement effect and steel amount.