Theoretical Analysis And Effect Research On Residual Stresses Of Thick-Wall Cold-Formed Steel

Because of economical efficiency of members and convenience of process, cold-formed steel members can be used more and more widely, with the advancement of technology, cold-formed steel members' thickness becomes larger and larger, and it tends to be far larger than traditional cold-formed steel members'. Currently, thick-wall cold-formed steel members have not been researched widely both here and abroad. Hence, it is of important theoretical significance and engineering application value for research on the performance of thick-wall cold-formed steel members.Facing one of the key problem- distributing patterns of cold-formed residual stresses after the wall' thickness increased, this paper gets along with study. Because simple, high efficiency , exact direct methods lack in present, this paper seeks for theoretical breakthrough. It is considered that the form processes of cold-formed residual stresses are similar to the processes of large deformation loading (bending) and reverse unloading (rebounding), based on the theory of plastic the stresses for the being formed stage are obtained, then using the ANSYS finite element software imitates the elastic restoration stage as to obtain the calculating values of the stresses for the elastic restoration stage; Finally cold-formed residual stresses are obtained by adding stresses acquired by the former two processes.After offering the theoretical analysis method, this paper compares the calculated values with the test values of residual stresses in cold-formed steel both here and abroad. It proves that the method is reliable. Then, residual stresses of thick-wall cold-formed steel members of 90 degrees are analyzed by this theoretical analysis method, and the factors of effect and the regularities of distribution are obtained: the magnitude and distribution of residual stresses have related with thickness relative bending radius; vertical residual stresses trend to increase from inside and outside wall to neutral layer through thickness, distributing relatively mild, unlike the distribution patterns assumed as linear of residual stresses in thin-wall cold-formed steel; distribution pattern of tangential residual stresses shows zigzag, and the value of residual stresses of simple point is maximum; total values of radial residual stresses are small, affecting the bearing capacity of members relatively small. Thus, theoretical foundation is formed for further test research and studying the performance on thick-wall cold-formed steel members affected by cold-formed residual stresses.Existing residual stresses bring some positions of steel structure members into plasticstate ahead, reducing buckling bearing capacity of members; in calculating buckling bearing capacity of steel structure members, good methods taking effect of cold-formed residual stresses into account directly have not been found. With the universal application of computer and development of numerical implementation, building member models fitting reality by computer can calculate buckling bearing capacity of axle loading members under effect of residual stresses. So, after obtaining the regularities of distribution of thick-wall cold-formed steel, this paper sets up actual cold-bending residual stresses model of bend angle of curl channel steel by ANSYS finite element software, creating ANSYS initial stresses file describing the distribution and magnitude of residual stresses, adding residual stresses into finite element model as initial stresses, analyzing buckling bearing capacity of thick-wall cold-formed curl channel steel column under effect of residual stresses, and comparing with no residual stresses. Study shows that existing residual stresses reduce the buckling bearing capacity of thick-wall cold-formed curl channel steel column, and obtains the result that degree of effect of residual stresses increases with increment of slenderness ratio.