The Ultimate Load Capacity Research Of The Web Opening C-shaped Cold-formed Steel Members Under The Influence Of Initial Imperfection

With the advantages of cold-formed thin-walled steel continually recognized by people,the application of Cold-formed components of web opening are also increasingly widely.Holes exist cause redistribution of membrane stress and affect the buckling characteristics of components and load-bearing capacity,making the analysis and design formula of the non-porous components is no longer applicable to hole components,it is necessary to study the cold-formed components with web openings.In order to study the ultimate bearing capacity of web openings of Cold-formed components,initial imperfections must be taken into account the impact.As one of the initial imperfections,the residual stress is very important to the overall stability of the component.Especially for web perforated members,the effects of residual stress are more complicated for the ultimate bearing capacity.However,because of the traditional mechanical measurements of residual stress are many defects, it is difficult to obtain its exact value.Therefore,the focus of this paper is to explore theoretically the size of residual stress in cold-formed and it's use of imposed in the finite element model of web openings of Cold-formed components.To study the Cold-formed residual stress field,in this paper, theoretical breakthrough is explored firstly,the cold-formed process of the members is divided into two stages:the bending process(loading) and rebound(unloading).The stresses in the member for each stage are derived respectively:based on the theory of elastic-plastic the stresses for the being formed stage are obtained,then using the Ansys-finite element analysis software imitates the elastic restoration stage as to obtain the calculating values of the stresses for the elastic restoration stage.Finally cold-formed residual stresses are obtained by adding stresses acquired by the former two processes.After offering the theoretical analysis method, this paper compares the calculated values with the test values of residual stresses in cold-formed steel both here and abroad.It proves that the method is reliable.In this paper,the assumption of cross-section residual stress distribution patterns of the web openings component is based on the cold-formed residual stresses that obtained above.Then,the initial stresses files which can describe the distribution and size of the initial stress are written.With the introduction of the document,we can obtain the stability limit load under the influence of residual stress,using the finite element analysis software ANSYS to analyze.Studies have shown that the method can be applied to simulate a variety of residual stress distribution,the existence of residual stress reduces the stability of ultimate bearing capacity of components with web openings.Finally,we use three web openings of thin-walled cold-formed C-shaped steel column for the study.It is assumed that the material for the ideal elastic-plastic body,and fully consider the impact of the initial defects,and using the finite element analysis software ANSYS to analyze the stability under axial compression.We have received to this conclusion:(1) The impact of bending on the ultimate bearing capacity of the components is greater than the residual stress.(2) Comprehensive initial imperfection on the ultimate bearing capacity of the affected components is greater than the impact of a single initial defects,but less than their sum.(3) Initial imperfection on the ultimate bearing capacity of the affected components with the hole size increases.(4) To consider the impact of a comprehensive initial defects in the web opening C-shaped thin-walled component finite element simulation,changing the tangent modulus has little effect on its results.We proposed that the project should be considered the general defects for its ultimate bearing capacity calculation.