Research On Ultimate Capacity Of Cold-formed And Hot-rolled Shs And RHS

The cross-sectional behavior of steel sections can be shown to be influenced by two extreme behaviors: the resistance and the instability.These boundaries are accounted for in current standards through a classification system consisting on rules depending on the crosssection dimensions.For example,in EN 1993-1-1,classes are divided into four classes.In this system,there exists a discontinuity between the classes 2 and 3 under pure bending load condition,while for the class 4,the effective width method(EWM)must be used to account for local buckling phenomenon.However,for non-linear materials such as cold-formed steel,the cross-section resistance can go beyond its plastic capacity due to strain hardening effects.Moreover,with the emergence of high strength steel and more complex cross-section shapes,the effective width method is becoming too complicated.In order to overcome these difficulties when evaluating the cross-section strength,the alternative methods including Direct Strength Method(DSM)and Continuous strength method(CSM)are developed over the last few years and recently has been adopted by some standers for the structure designs of hot-rolled steel,cold-formed steel,stainless steel and aluminum alloy,etc.Hot-rolled and cold-formed square and rectangular hollow sections(SHS/RHS)are mainly considered in this thesis.This thesis investigates the possibility to extend the DSM to hot-rolled structural steel cross-sections and the CSM to cold-formed ones.The investigation of the local buckling behavior and the design method of hot-rolled and coldformed SHS/RHS is studied in this thesis.The main contains are as follows.(1)A nonlinear-finite element model considering both local imperfections and residual stresses was established using ABAQUS and validated against existing test results.(2)Upon validation of the finite element models,parametric studies were performed to assess the ultimate capacity of SHS/RHS over a wider range of local initial imperfection amplitudes,cross-section slenderness,cross-section aspect ratio material yield strength and interaction effects.(3)By comparing the FE analysis results with the corresponding European,American and Chinese design provisions,it is confirmed that the design methods for the ultimate capacity of SHS/RHS under different load conditions need to be modified.(4)Modified DSM expression for slender hot-rolled cross-sections and CSM expression for stocky cold-formed cross-sections were then proposed in this study,and reliability analysis was also carry out to assess the reliability of the proposal expressions.