Slabs-Disassembled Analysis On Thin-Walled Open-Profile Members

Only under pure torsion conditions could cross-sections of a thin-walled open-profile member warp equally, the longitudinal stresses due to the nonuniform longitudinal distribution of warping yield shearing stresses that would cause warping torque, which is not neglectable for thin-walled open-profile members. Based on the hypothesis of Rigid Section Sharp, V. Z. Vlasov set up a theory to analyzing this type of members. His methods were wildly used when analyzing steel members and thin-walled members, such as their flexural-torsional buckling, but his theory was too complex to use, which was the same with the theory of flexural-torsional buckling.In this article, warping was regarded as the most important factor when the torque is not uniform along the member length, and the relationships between warping and distortion, torsion and bending were managed in different ways. As a result, a new measure of analyzing thin-walled members was put forward.The resistance of the thin-walled open-profile bar was divided into several parts. Firstly, the resistance system against in-plan stretch-bending of slabs was discussed, which was believed characterizing the mechanical property of thin-walled members in this article. It was found that this resistance system was much the same as that of an in-plan flexured bar. Then, the thin-walled open-profile bar was regarded as a hyperstatic structure while the resistance system against in-plan stretch-bending of slabs it's basic system, the resistance against free torsion could be looked on as the redundant force. Thus, a new method analyzing the thin-walled open-profile member considering restricted torsion was set up, which could obtain the same conclusion as the conventional method given the same promise. While the latter had to concentrated a bar to it's axis of shear center,the former could provide flexible integration of slabs-disassembled analyses in form of matrix.Fictitious loads of flexural-torsional buckled members were decided slab by slab in this article. For each slab, the procedure was not much different from that of bars buckled in-plan. A new method of the flexural-torsional buckling of the thin-walled open-profile member was then set up by combining analyzing of all it's slabs. This method was applied to those normal steel members, too.Progress of the flexural-torsional buckling theory was accompanied by controversies since Wager. New researches considered more and more non-linear factors, but in this article, some complex factors such as the Wagner term were not need to be considered.It was necessary to analyze the distortion of thin-walled open-profile members because sometimes they may fail because of local buckling or distortional buckling. Another sort of redundant force, resistance system against distortion, was considered in this article. By simplifying the resistance against distortion and the transfiguration of cross-section, a simplified method was put forward at first, which was easy to understanding and applying. Then, a more accurate method was proposed, simplifying measures were not necessary.Generally, steel members were thin-walled, the thin plate were prone to local buckling and distortional buckling. The latter held the interests of nowadays researchers. A new linear buckling analysis method considering all the possibility of local, distortional and global buckling was put forward then.Direct Strength Method is an entirely new method for the design of thin-walled members by whole section instead of effective section. Direct Strength Method need the critical load results of local buckling, distortional buckling and global buckling mode. It was noticed that the knowledge about distortional buckling mode at present was not enough, so the fictitious load conditions of distortional buckling mode was deduced in this article. As a result, a new approach for buckling mode definitions of thin-walled open-profile members were proposed, which, unlike the existing phenomenological definitions, are based on simple mechanical assumptions which can easily be applied in the context of any numerical method.Three basic opinions on analyzing thin-walled open-profile members in this article were as follows. Firstly, warping and distortion were not necessarily antipathic. Secondly, orthogonality relation between warping and bending was not need to consider. At last, concentrating a bar into any axis was not necessarily. An entirely new methodology based on the three new views was set up in this article, which was proved to be reasonable and effective.