The Stability Of Portal Frame Analysis

Steel structure of portal frame with steel of high strength,can do more light and softly,this makes the stability problem is especially prominent.Stability problem belongs to the second order,that is,after the need to consider the balance,and the intensity of the traditional first-order problem only deformation must be considered before the balance,so the stability of second order complex problems than the strength of the first order problem,belongs to the geometric nonlinearity.Stability is the core of solving the stability bearing capacity of the structure of the bar or(namely,critical force).Although single bar critical force is not difficult to solve,but it requires the solution of the critical load of the whole structure is not easy.In the current specifications for design of steel structures(GB50017-2003)with solving frame of calculated length coefficient form(see appendix D),but the form implied some assumptions,the rules can only be used for rigid frame(each column axial force is the same),and for irregular frame column axial force different()is no longer apply.Nor does the other specification can determine the oblique beam gantry frame calculated length coefficient formula or form.Aiming at the status quo,this paper from the gantry frame(including the oblique beam door frame),derived the critical equation of the stability of the whole frame(transcendental equation),and then solve,after thousands of times of solving into,received a large amount of data,made the calculation length coefficient of frame column of nomograph.Use the nomograph can quickly calculate the pillars of the calculated length coefficient.This paper is the most valuable achievements in appendix A-C nomograph,the correctness and reliability of the nomograph is through the test of finite element calculation,and the calculation precision is very high.Is a rapid calculation of irregular gantry frame column critical force of good tools,in the face of the steel structure design code is not yet the calculation table,is also a supplement.In my master's stage,the stability theory has experienced from the initial strange,to the middle of the familiar,to the late love,is can feel do in-depth research,the rest of the time is running out.In addition,the overall stability of the solution for multiple pole structure,the number of unknown variables with the bar and the number of nodes increases,lead to want to get the final resolution increases the difficulty of the critical equation,such as:how to use hand order reduction amounted to contain numerous transcendental function of higher-order determinant?Are the questions I encountered,also limits the analytical method used in more complex structures.On the other hand,let me also see:from research work about the irregular structure(each column axial force is not the same)critical force calculation,there are a lot of work to do,these structure more in line with the actual load conditions,but hard to find in the present code of some of the relevant calculation formula or form.This paper also did some work in terms of parameter analysis,some critical force of frame column are obtained with the tendency of changes in the parameters.