Study On Flexural Capacity Of Thin-walled Flitch Filled Rectangular Steel Tube Composite Beams

With the promotion of the housing industrialization,the cold-formed thinwalled steel structure gradually increased in China in recent years.But the wallthickness of cold-formed thin-walled steel is thinner,and has large widththickness ratio.So it's easily to trend to unstable failure under the compression state,then the strength of steel can not be fully exploited.Taking the beam in coldformed thin-walled steel structure as the research object,this paper studied the measures to improve its flexural capacity,and put forward the thin-walled flitch filled rectangular steel tube composite beam.In order to study the flexural performance of this composite beam,the bending performance test of rectangular section cold-formed thin-walled steel beams,sylvestris beams and composite beams was carried on.And the numerical simulation was carried on by the finite element software ANSYS in this paper.Then the combined effect of composite beam was analyzed by comparing flexural capacity and flexural rigidity of the three kinds of test beams.And the effect of width-thickness ratio and depth-width ratio on the flexural performance of composite beam was discussed.Lastly the calculation formula of ultimate bending bearing capacity of composite beam was proposed.The main contents and conclusions of this paper are as follows:(1)Through the flexural performance test of steel beams,wood beams and composite beams,observed and recorded the failure process and failure phenomenon of each test beams,and compared the load displacement curve and initial bending stiffness of the three kinds of test beams.The results show that the steel tube and flitch can work together,and the composite beam shows great combination effect.Besides,the composite beam shows great ductility compared with steel beam after reaching the ultimate load.(2)The finite element model for composite beam was builted by using finite element software ANSYS,and the validity of finite element model was proved by comparing with the experimental results.And basis on the finite element model,the effect of width-thickness ratio and depth-width ratio on the flexural performance of composite beam was discussed.The results show that the ultimate flexural capacity and ductility of composite beam increase gradually with the reduction of width-thickness ratio;and the ultimate flexural capacity of composite beam increase gradually with the increase of depth-width ratio,but the ductility declined slightly with the increase of depth-width ratio.So it is suggested that the width-thickness ratio should be taken as the main analysis parameter of this composite beam in practical engineering application.(3)The basic calculation assumption for ultimate flexural capacity of composite beam was put forward.Basis on the basic calculation assumption,analyzed the whole process of the load deformation of composite beam,and the validity of basic calculation assumption was proved by comparing with the FEA result of cross middle moment curvature curve.Lastly,the calculation formula of ultimate bending bearing capacity of composite beam was deduced in the paper,and the difference between formula calculation and finite element calculation is relatively small,the deviation was controlled within 20%.The calculation formula can provide reference for practical engineering.