Research On The PMM Yield Strength Surface Model And Capacity Tests Of Cold-Formed Multi-Roll Lipped Channel Columns

With the advancement of technology and rapid development of the construction industry in recent years, cold-formed thin-walled steel members have made great progress in the application in building structures, long-span structures and storage structures. Owing to the superior strength to energy ratio and environmental protection, cold-formed thin-walled steel members have been widely used in the storage structures, which greatly promoted the development of logistics and warehousing. As the mainstream storage structures, assembled steel storage racks are built larger and larger, higher and higher. This trend of development puts forward stricter requirements for the safety of storage racks. Above all, experimental study and numerical analysis have been conducted on cold-formed multi-roll lipped channel columns called N90 of storage racks in the thesis to investigate the distortional buckling behavior of the members. Then, a three-dimensional P-M1-M2 yield strength interaction surface was built, and the current specification approaches under bi-axial force were evaluated. At last, parameters for the plastic hinge of columns conducted in this paper were provided.On the basis of an overall review of elastic distortional buckling analysis and strength design method, material property tests were performed on 15 tensile coupons and failure tests were conducted on 1 axially loaded and 14 eccentrically loaded N90 multi-roll lipped channel columns. The material property tests revealed that the cold work hardening effect of steel in the corner area was prominent and the ultimate stress was about 35% higher than that in the flat plate area. The failure test of multi-roll lipped channel columns obtained the failure phenomena, the load-displacement curves, the load-rotation curves and the ultimate capacities of axially and eccentrically specimens. It turned out that the eccentric direction and eccentricity had great influence on the mechanical behavior of the specimens. More specifically, when the load point was close to the web and away from the flange, the specimen failed in local buckling, otherwise, the specimen failed in distortional buckling.Numerical analysis has been completed on the N90 multi-roll lipped channel specimens using finite element software ABAQUS. Especially, three kinds of initial geometric imperfection models were studied, Three finite element models with different initial geometric imperfection models were established, and the ultimate bearing capacities and the failure modes of the analysis results were compared. The results showed that the geometric imperfection modeled as a combination of the first five buckling modes was more suitable to the N90 section specimens, and the finite element model was verified against the experiments and yielded good agreement.Finite element analysis of the 343 specimens with various eccentric loading was completed by employing the finite element model in this article and calling ABAQUS through Matlab. Then, the PMM yield strength surface model based on finite element analysis was fitted, which was made comparative analysis with another surface model based on DSM and current specifications in AISI-S100-12, and the application of it in advanced analysis was studied. Results showed that for the N90 section columns in this paper, the current design under combined actions in AISI-S100-12 had certain applicability, but was quite conservative and needed to modify. It is recommended that the design could try a nonlinear combination. For singly symmetric cross-sectional members studied in this paper, when subjected to non symmetric axis bending moment, the capcities calculated by DSM were in poor agreement with the finite element analysis, and the results were not safe. It is recommended that the bending bearing capacity formulas of DSM should be modified. The PMM yield surface based on finite element analysis was processed to obtain eight PMM curves in different phase angle plane, which can be implemented in the structural analysis software to define the plastic hinge of N90 section columns.