Performance Research On Local Buckling And Distortional Buckling Of Cold-formed Thin-wall C-section Steel Flexural Members

For the cold-formed steel, there are three buckling modes, including local buckling,distortional buckling and lateral-torsional buckling. Local buckling and lateral-torsionalbuckling are researched in previous time, the recogization of distortional buckling waslate and its own complexity, many research results are not comsentaneous and needfurther study. Two methods are used for design the cold-formed thin-wall steel:Eiffective Section Method (ESM) and Direct Strength Method (DSM). The ESM is usedfor design for many country’s codes, but this method is only suitable for local bucklingof members, is not suitable for distortional buckling, and it is extremely complex forcalculate the effective width and its sectional properties. DSM is considered bucklingmode by the reduced strength and its calculating process is simple. In summary,application of DSM will be gradually extended and development of DSM is imperative.At present, study on the stability behavior, especially distortional buckling ofcold-formed thin-wall steel are not adequate in our country, so ESM is still used in ournational codes.To complement our national research results and provide experimentaland theoretical basis for application of DSM, this paper investigates the local bucklingperformance, distortional buckling performance and bearing capacity of cold-formedthin-wall C-section steel flexural members by tests investigates and theoreticalanalysis，mainly completed the following works:①Investigating the local buckling and distortional buckling performance forcold-formed thin-wall C-section steel by tests. The experiment was divided intotwo groups with12members (24specimens), local buckling and distortional bucklingperformance were studied by changing the geometric parameters of the test section,measuring strain and deformation of whole force process, it could provide theexperimental basis and comparative basis for later numerical simulation. Local anddistortional buckling phenomenon were observed in the tests process and verified layingof a certain thickness steel plate on the pure bending could guarantee local bucklingoccurred, this result show that boundary condition can influence buckling modeeffectively.②Based on the test results, verified reasonability and applicability for cold-formedthin-wall C-section steel’s finite element model. The imperfection shape is obtained byusing the finite strip software CUFSM, imperfection size is determined by CDF values for maximum imperfection and considerd geometric and material non-linearities and thegeometric non-linearities in the model. The analysis results show that, analysisof cold-formed thin-wall C-section steel’s finite element model is reasonable andeffective.③A series of variable parameters simulation analysis is reasearched localbuckling,distortional buckling performance and bearing capacity for cold-formedthin-wall steel. Study influence law of local buckling,distortional buckling performanceand bearing capacity for cold-formed thin-wall steel with different web height, flangewidth, edge stiffene width and plate thickness. The results show that, thereare correlations between influence factors, all the factors have a important effect forbuckling mode and bearing capacity. Within a certain range, increasing section area andplate thickness can improve bearing capacity. Meanwhile plate thickness and ratio byflange width and edge are an important factor affecting thebuckling mode.④Taking the original DSM formulas as standard, revised the original DSMformulas for flexural member by using this paper tests results, parameters analysisresults and other reasearcher’s tests results, and validated the new formulas. Thevalidateing results show that there is a little deviation,the revised formulas can give areasonable prediction for bending capacity of beams.