Analysis Of The Overall Stability Of I-section Members Under The Action Of The Bracing Systems Composed Of Knee Brace And Purlin

I-section members belong to open thin-walled members,their can be used as the main force member for flexural,compression and bending,and their overall stability is one of the important influencing factors of structural bearing capacity.In engineering,in order to improve the overall stability performance of I-section members,it is common practice to increase the width of the flange plate of the member or to provide lateral support.Increasing the width of the flange plate can increase the lateral bending stiffness and torsional stiffness of the component,and achieve the purpose of improving the overall stability of the component;setting the lateral support reduces the calculated length of the component out of the plane,and improves the stable bearing capacity of the component.In the design of the portal frame structure,k Nee braces are generally set on the roof and wall,The k Nee braces and purlin together form a brace system,and the two work together to provide support for the beam or column.In this paper,the problems in the research on the overall stability of I-section members with the bracing systems composed of k Nee braces and purlins are further studied.The research mainly includes three parts: theoretical analysis,finite element analysis,and engineering application analysis.The main contents are as follows:(1)Theoretical analysis.This paper expounds the action principle of brace system on I-section members,puts forward the theoretical analysis model of the overall stability of I-section members under the action of brace system,and gives the calculation method of the support stiffness.By using energy method,the critical load expressions of I-section flexural and axial compression members,I-section flexural and axial compression members are derived.(2)Finite element analysis.The buckling critical loads of equivalent section members and wedge-shaped members are calculated when the buckling deformation is U-shaped and S-shaped respectively,and the stability of steel beam under two kinds of buckling deformation is compared.And the critical stiffness expressions of the bracing system for the full support of the four I-section members are obtained.And the results of the finite element analysis are used to verify the critical load expressions forthe torsional buckling of the I-section members.And aiming at the problems in deriving the critical load expression of torsional buckling of I-section wedge beams,the correction factor for the calculation of the critical moment of torsional buckling is obtained through the finite element analysis.And simplified formulas for calculating the out-of-plane length factor for axially-compressed steel columns with I-sections with unevenly-spaced bracings in 7 typical cases is given.(3)Engineering application analysis.Based on theoretical analysis and finite element analysis,and combined with the problems in the project,suggestions are made for the overall stability calculation of the portal rigid frame beams columns with the bracing systems composed of k Nee braces and purlins.