| The stability problem of cold-formed thin-wall steel structures is very complex.It is experienced two research stages,effective width method and direct strength method.Based on the effect of the local buckling of the plate on the bearing capacity of the member,specification cold-formed thin-wall steel structures all over the world take the method of the effective cross section to calculate the bearing capacity of member at present,considering the influence of local buckling of the member on the overall buckling of the member,the calculation of the strength and stability is carried out with the partial effective section,however,this method neglects the effect of the distortion buckling performance of the component.The effective width method in the application process,the effective width and its geometric characteristics is a complex process,especially for the complicated calculation section will be more difficult,the current development of cold-formed steel structure,the plate thickness is thinner,higher yield strength of plates with intermediate stiffeners and complicated section form,usually the distortional buckling control,effective width method gradually shows disadvantages.The direct strength rule by using the whole section to calculate all kinds of parameters on the strength reduction,without calculation of finite width and effective section properties for each section of the plate,it can consider the effect and related buckling modes on the stability of various individual components.This method represents the development direction of design method of cold-formed steel,still need to carry out theoretical and experimental research work,the method can only calculate the ultimate bearing capacity of columns and simply supported beam under pure bending of simply supported shaft,the bearing capacity of more complex cross-section form,stress state and boundary conditions the calculation remains to be studied.In this paper,the cold-formed C-section steel under bi-axial eccentric compression has been analyzed by using experiment and finite element analysis,which concludes the stable performance?ultimate bearing capacity and direct strength method based on P-M1-M2 relationship.The effective width method is replaced.A calculation method of ultimate bearing capacity has been proposed for the cold-formed C-section steel.The following is the main contents and conclusions of this paper:(1)The bi-axial eccentric compression test of 52 specimens with the same section shape and two length of members was completed.The influence of specimen length and eccentricity position on the stability and failure modes of the specimens was studied.The experimental results show that the deformation of bi-axial eccentric compression member is composed of the local buckling of the plate,the rotation of the flange roll,the rotation of the composite body and the overall bending deformation of the member.In the condition of the same geometry,it eventually distorted eccentric component instability accompanied by overall bending;negative eccentric component,round strong axis eccentricity is small,the failure mode of the local buckling and bending with the overall,with the increase of round strong axis eccentricity,failure mode gradually to appear in local buckling and distortional buckling and buckling mode with overall bending;with the increase of the length of component,reduce the bearing capacity of components with same eccentric position,overall bending phenomenon with the more obvious;limit the size and direction of eccentric distance of specimens had a significant effect on the bearing capacity.(2)The stability and bearing capacity of cold-formed thin-walled C steel members subjected to biaxial eccentric compression are simulated and analyzed by the finite element method.First of all,the rationality and validity of the finite element model are verified on the basis of the experimental results.On this basis,the finite element model is applied to the analysis of parameters,the variation of various geometric parameters and the member length and eccentricity position were investigated the influence of instability mode component and the bearing capacity of the test results were added.The research shows that the effects of eccentricity on the position and thickness of the component member buckling mode and the bearing capacity of the most significant distance is eccentric around the weak axis,the main component distortion and instability,with the overall bending,component is long,with the overall bending distance is more obvious;negative eccentricity around weak axis,eccentric round strong axis distance is small,the main component occurs local buckling,and accompanied by the overall bending,with round strong axis eccentricity increases gradually with the component of distortional buckling is the main failure mode;bearing force around the weak axis eccentricity influence,eccentricity increase the load-carrying capacity;load-bearing capacity of member thickness is bigger;the edge length effect on the bearing capacity of buckling distortion of large.(3)According to the analysis result,according to the different instability mode presents a calculation method of bearing capacity of bi-axial eccentric direct strength method based on the relationship of the bi-axial eccentric P-M1-M2.The experimental results show that the proposed method can effectively predict the ultimate load-carrying capacity of cold-formed thin-walled steel members subjected to bi-axial eccentric compression. |
PDF Full Text Request