The Overall Buckling Mode Identification Method And The Stable Ultimate Bearing Capacity Calculation Of Long-span Steel Structures Based On The Energy Method

Steel is widely used in a variety of building structures because of its high strength, lightweight and good mechanical properties. Compared with the reinforced concrete structures inthe case of the same force, the cross-section of the steel components is small, the componentslenderness ratio is large and the plate thickness is thin, so the components and panels in thecompression zone are easily leaded to structural instability. In particular for the large spansteel structure with the increasing scale and the more and more complex forms, the stability ofsteel structure should be paid enough attention.Firstly, on the basis of numerous thesises, the paper makes a comprehensive introductionto the basic instability theory of the steel structures and the research method of the stableultimate bearing capacity which is the fundamental work of the subsequent analysis.Secondly, the eigenvalue buckling analysis of the conventional steel models was runbased on the finite element analysis software ANSYS with a different number of units. It wasfound from the results that the buckling load was greatly influenced by the unit number whenthe eigenvalue buckling analysis was run with the conventional Timoshenko beam element.The result would be more precise only when an appropriate unit number was used.Thirdly, the eigenvalue buckling analysis of the conventional steel models was run basedon the finite element analysis software ANSYS and a method to differentiate the overallbuckling modes was proposed after the results were analyzed and summarized by the VBAprogram. The method reflects the relationship between the overall buckling modes and theoverall modal strain energy of the structures under static loads. The overall modal strainenergy in the overall buckling mode was much higher than that in the local buckling mode. Sothe overall buckling mode can be filtered through the overall modal strain energy. Themethod was applied in practical engineering in the paper and had a good effect.And then, learning from the consistent mode imperfection method, all the eigenvaluebuckling modes were considered to simulate the initial deformation distribution of thestructure and the geometric nonlinear analysis was run of the conventional steel models andpractical engineering structures under static loads to get the stable ultimate bearing capacity ofthe structure. Then it was found that there was a lack of consistent mode imperfection methodthat the stable bearing capacity calculated by the consistent mode imperfection method wasnot conservative while the higher order buckling modes of defect distribution model may bemore unfavorable for certain structures.In addition, an improvement measure of the consistent mode imperfection method was proposed in the paper. A specific area of eigenvalue buckling modals corresponded to the firstcatastrophe of the overall modal strain energy in the graph of the overall modal strain energywas screened out and the stable ultimate bearing capacity was got through the nonlinearanalysis. The method was applied in the conventional steel models and practical engineeringin the paper which showed a good effect.In the end, problems and baffles during the process of the research on the stabilityanalysis of the steel structures are listed, limits and shortages of the new method are explainedand the future of the researches on the stability analysis of the steel structures is tentativelypredicted.