Mechanism Of The Static And Dynamic Distortional Buckling Of C-section Cold-formed Thin-walled Steel Members

Cold-formed thin-walled steel members have been widely used in constructions due to its advantages such as light weight, good mechanical properties, short production cycle, easy-toassemble and so on. With the development of metallurgical technology in recent years, coldformed steel members have been developed in a direction to high-strength, thin-walled, complex cross-sections. Steel members’ local buckling stability had been greatly improved, so distortion buckling turns into the important factor in controlling the ultimate bearing capacity. It is very necessary to do sufficient researches on the stability of the C-section cold-formed thin-walled steel members which is commonly used in the steel roofing-sheeting systems. A thorough study on the static and dynamic distortional buckling mechanism has been made in this paper.Firstly, CUFSM program is employed to study the influence of the oblique lips’ angles on the critical distortional buckling stresses of C-section steel members undergoing compression or bending. Direct Strength Method(DSM)was applied to obtain the post-distortional buckling ultimate bearing capacity of each steel member, the results were compared with the calculation results of steel members with upright lip. The results indicated: post-distortion buckling ultimate bearing capacities in both compressed members and flexural members have been improved at different degrees when the angle of the lip between 90o to 120o, and the ultimate bearing capacities are enhanced obviously at about 105o in most members.Then this paper proposes a holistic approach model which is based on the present study on the distortional buckling mechanism for the C-section steel structure at home and abroad. In this paper, the proposed model has broken the previous tradition that adopting various spring instead of the suppport on the combination of flange and lip by web during the analysis process. The energy balance equation was used to replace the previous force balance equation on the basis of Timoshenko elastic stability theory to make the holistic approach to both compressed members and flexural members. Then using Hermite rectangular element interpolation function to solve the energy equation to obtain the distortional buckling critical loads of the compressed C-section coldformed thin-walled steel members.The analytical results are compared with those by finite strip and the validity of the model is verified.Finally, the axial compression tests on C-section cold-formed steel members are proceeded by using drop hammer. In order to determine the buckling mode and obtain the load-displacement curves, high-speed photography instrument and speckle techniques are used to analyze the deformation of the sample. Meanwhile comparing the test results and the numerical simulation results by finite element soft ware ABAQUS to judge the dynamic buckling modes and verify the precision and accuracy of the stress-strain curve. The static and dynamic distortional buckling mechanism on C-section thin-walled steel members are proposed through the combination of the above analysis.