Study On Axial Compression Stability And Mechanical Model Of Websteel Composite Wall

Websteel structure system is a member of the cold-formed thin-walled steel structure system,which has advantages of light weight,high strength,rapid assembly and convenient pipeline layout.Extending the system from low-rise to multi-storey buildings is helpful to accelerate the process of building industrialization in our country.As the main load-bearing structural components of the system,it is particully important to study the stability of the composite wall under axial compression.However,the existing design methods of composite wall is not fully considering the constraint effect of wallboard,which leads to the over-conservative design of composite wall bearing capacity and hinders the application of websteel structure system in multi-storey buildings.Therefore,the axial compression stability and mechanical model of the websteel composite wall are systematically studied in this paper.First of all,the axial compression stability of two and four-tube built-up column and composite wall were experimentally investigated in full scale.The linear elastic buckling performance of two and four-tube built-up column and composite wall were numerically analyzed by spline finite point method and QR method.Then a finite element analysis(FEA)was performed to investigate the influence of various factors on the elastoplastic stability of two and four-tube built-up columns.According to the linear elastic research,the design specifications for two and four-tube built-up column were modified and some suggestions were put forward.Moreover,based on the existing wallboard constraint theory and topology analysis of wallboard shear behavior,the mechanism of wallboard constraint was explored.Finally,a new design method for the bearing capacity of composite wall in compression was proposed,which took into account the wallboard constraint.The main contents and achievements are as follows:(1)Experimental study on the axial compression stability of two and four-tube built-up column and composite wall was carried out.A detailed experimental study was conducted on the axial compression stability of 4 two-tube built-up columns,12 fourtube built-up columns and 6 composite walls.The failure mode,load-displacement curves,strain distribution and ultimate bearing capacity of three kinds of specimens were studied,taking into account the influence of parameters belonging to two-tube built-up columns including column length,thickness of tubes,distance between tubes,parameters belonging to four-tube built-up columns including connectors' type,distribution of connectors,distance between connectors,distance between tubes,and X-type transverse diaphragm,as well as parameters belonging to composite wall including number of sheathing and type of sheathing.The experimental result showed that the maximum bearing capacity of the wall with double-side sheathing is 3.1 times that of the wall without sheathing,and the maximum bearing capacity of the wall with single-side sheathing is 2.0 times that of the wall without sheathing.This indicated that the constraint effect of sheathing to studs is obvious.(2)Numerical study on the linear elastic and elastoplastic stability of two and fourtube built-up column was performed.The calculation method of critical elastic buckling load for two and four-tube built-up column were studied by spline finite point method and QR method respectively and programmed by C language.In addition,the elastoplastic buckling performance of two-tube built-up columns was numerically analyzed by finite element method,and the influence of key factors on ultimate bearing capacity was discussed.The buckling stress of the existing design codes for coldformed thin-walled steel structures was modified by using the results of linear elastic research.The design suggestions for two and four-tube built-up columns were proposed.The results showed that the critical buckling load calculated by spline finite point method and QR method was consistent with the finite element solution.The predictions of AISI-S100-12 and GB50018-2002 were in good agreement well with the experimental results.(3)Theoretical study on the constraint effect of wallboard was conducted.Based on the existing theoretical assumption of the wallboard constraint,the mechanism of the wallboard restrict against the stud was revealed through the extrusion test and the shear-behavior topological analysis of the wallboard.Furthermore,a mechanical model considering the extrusion stiffness and shear stiffness of the wallboard was proposed,i.e.combined stiffness model.Analytical formulae for various stiffness were provided.The results showed that the response of whole wallboard induced by shear deformation is similar to that of cross-wattle structure.The calculated values of derived shear stiffness formula were closed to those of the formula of shear stiffness of whole plate.In addition,the analytical formula of extrusion stiffness can provided the upper bound for the extrusion stiffness of wallboard.(4)Numerical study on the linear elastic and elastoplastic stability of composite wall was developed.The linear elastic in-plane and out-of-plane buckling critical load calculation program for the composite wall with evenly distributed spring braces was derived according to spline finite point method and QR method,and programmed by C language.In addition,on the basis of linear elastic buckling analysis,the critical load of composite wall was nonlinear modified.Combined with the existing design regulations of composite wall,a new design method for the bearing capacity of composite wall in compression was presented,which took into account the wallboard constraint.The results showed that the difference for bearing capacity of composite wall between tested results and calculated values according to the combined stiffness model was no more than 7%,which verified the accuracy of the combined stiffness theory.The design method proposed in this paper can be used to design the bearing capacity of composite wall in compression.