Study On Stability Of High-strength Cold-formed Thin-wall Lipped Channel Steel Under Axial Compression

Due to the characteristics of thin-wall,the stable bearing capacity plays a crucial role in the design of cold-formed thin-wall members.The influence of distortional buckling isn’t included in the current Chinese Cold-formed Steel Specifications,which is mainly based on Q235 and Q345 steel.With the continuous improvement of section thickness and material strength,the distortional buckling plays a leading role in bearing capacity of components in many cross section forms.Hence,it is necessary to study the local-distortional coupled buckling performance of high-strength thin-walled components.In this paper,the interaction between local and distortional of high-strength cold-formed thin-wall lipped channel steel columns are studied by experimental and numerical methods,and the stability bearing capacity of thin-wall channel steel columns is calculated based on the Chinese and American codes.The main contents are as follows:(1)The calculations of elastic buckling loads and stability bearing capacities of cold-formed steel members were summarized,and the differences in several common calculation methods of local and distortional buckling critical loads were compared through numerical examples.It is shown that the local buckling critical loads obtained from local buckling theory formulas are lower than that obtained from the numerical methods,if not considering the panel correlation(AISI specification),the calculation results are too conservative.The calculation results of GBT are the closest to that of FEM,and its fluctuation is the smallest,followed by the FSM.The distortional buckling critical loads and variation trends calculated by Hancock model and FSM are similar,and the Schafer model is similar to GBT.(2)A series of axial compression tests were conducted on 24 high-strength cold-formed thin-walled lipped channel columns to investigate the stability bearing capacity and deformation of test specimens with different web depth,lip width and length.The experimental results indicate that: the shorter members with large web and lip are more likely to occur interaction between local and distortional.The local buckling come first and then distortional buckling appear for all specimens undergoing local-distortional coupled buckling.The largest deformation of distortional buckling mainly occur around the mid-height of the specimens,and the combination of flange and lip are expanding along the entire specimen length.(3)The finite element model of test specimens was established using ABAQUS software to study the influence of different initial imperfection shapes and material models on bearing capacity and deformation of the specimens compared to test results,and the parametric analysis was also performed.It can be conclude that the web depth and lip width are more sensitive to local and distortional imperfection,respectively.The lip width has the greatest influence on the bearing capacity of the specimens,followed by the specimen length and web depth.Increasing the lip width can obviously improve the bearing capacity of the specimens.The failure modes of specimens will not be affected by the increase of yield strength which can increase the deformation degree of specimens and lead to the lower strength utilization rate.The specimens are more prone to distortional failure due to the increase of section thickness,and the strength utilization rate will be higher.(4)It was the bearing capacity of the test specimens and the numerical simulation specimens as well as the test specimens collected from other literatures that were calculated using the design methods in Chinese and American specifications to analyze the differences and accuracy of the both,thus the reasonable suggestions were put forward for further improvement of design codes.It can be demonstrated that the bearing capacity of specimens based on direct strength method of the Chinese specifications(draft)and the effective width method of the American specifications have a good fit with the experimental results;the calculation results of the effective width method of the Chinese specifications(draft)is conservative,and the calculated bearing capacity of all specimens is smaller;the bearing capacity of specimens based on the direct strength method of the American specifications is the largest,unsafe and fluctuate the most.