Research On Ultimate State Of H-Section Steel Beam-columns Under Combined Biaxial Bending And Axial Force

The actual seismic external loads have features of arbitrary direction,acting dynamically and 3D spatiality.For the columns under combined biaxial bending and axial force in the structure,the interactive effects on strength,stiffness and plastic deformation capacity of steel members caused by biaxial moments would increase structural response.Therefore,to predict accurately the seismic behavior of the structure under actual earthquakes,it is necessary to propose a design method that takes into account this interactive effect.Since the research on biaxial bending behavior of H-section steel member dominated by local buckling is quite limited,it is necessary to investigate the nonlinear performance of such members.The main research object of this paper is the Hsection beam-column member in low-multistory frame and the research focus on the nonlinear performance at the end region of the member.Experimental study is an important part of seismic behavior research to structure members.The reasonable loading scheme and test device design of the experiment is important for the study of seismic behavior of beam-column members under biaxial bending moment and compression.This paper analyzed the loading features of beam-column members under vertical load and biaxial horizontal earthquake action,explained the significance of biaxial bending and compression tests on cantilever columns for seismic behavior of beam-column.Through reviewing the research on biaxial bending and compression tests which were carried out at home and abroad,this paper summarized 5 kinds of typical loading schemes,and then analyzed the characteristics of different loading schemes and requirements for testing device,for the reference of relevant researchers.As the important component of seismic behavior,the ultimate capacity of columns is the conventional engineering design index and is the direct reflection of resistance for structural members.So the research focused on the ultimate capacity of H-section members under combined bending and axis force.Based on the energy conservation principle,an approach to determining the ultimate state of H-section members under biaxial bending by the inflection of energy was proposed.In addition,the finite element analysis program ABAQUS was used for the analysis.FEM models of H-sectional cantilever beam-columns under combined biaxial bending and axial force were established,considering the effects of material nonlinearity,geometric nonlinear as well as the initial geometric imperfections.The models were validated by the available test results.To investigate the ultimate performance of H-section members,parametric analysis based on FEM models was conducted,considering different combinations of loading direction,width-thickness ratio,axial force ratios.First,different failure models were numerically investigated.Then,based on the stress distribution property at the ultimate state and development of biaxial bending moment,the reasonability of the approach to determine the ultimate state of H-section members under combined biaxial bending and axial force was verified.Furthermore,the effects of loading direction,flange and web width-thickness ratios,axial load ratios were discussed,and the mechanics of plate interaction at the plastic stage was simply investigated.Finally,the interactive curves of biaxial moment resistances determined by EIM(Energy Inflection Method)were obtained,and the interactive equations for design purpose based on Effective-Plastic-Width method were proposed.The ultimate state interactive equation was compared with the Eurocode EN 1993-1-4,and it is obtained that the equation extracted in this paper is more accurate and reasonable.