Overall Stability Research Of Steel I-Beams Under Combined Bending And Torsion

The characteristics of steel determine the bearing capacity of the steel structure, in most cases it is not by strength of materials, but by stability, and overall stability is the core content of the stability problem. The researches of the steel beam integral stability problems inside and outside have achieved fruitful achievements, but the study about the overall stability of the steel I-beam suffering combined bending and torsion which is very important in practical engineering is still rare, and there are no formulas for calculating the overall stability of steel beams under combined bending and torsion in Code for design of steel structures(GB 50017-2003) also. Thus this paper argues that it is necessary to have a further study, and strive to get a applicable and succinct formula that can be used for engineering design, so as to provide reference in next revision on Code for design of steel structures.Firstly this paper introduced and compared the present several different overall stability theories, and pointed out some shortcomings of them, then got the conclusion that traditional theory result was correct. On this basis, the pape deduced a four-order inhomogeneous abstract differential equation by energy method, because this equation is difficult to get analytical solution, so by profitting from the ideas of design code for steel ,and identifying important influence parameters, the paper put forward a new equivalent bending moment coefficientβregarding the load case of combined bending and torsion,so that the computation formula by bending stable had the same form with the formula in Code for design of steel structures.In order to research the equivalent bending moment coefficientβ, this article built four models of two eccentric loading cases and two different action spots and did a series of numerical calculation,then compared the calculated data with results in code of cold-formed thin-wall steel structures(GB50018-2002)and analyzed the two important factors e &ξ, furthermore, had a qualitative knowledge of the problem. From all of this, the article obtain four kinds of fitting formulae and parameter values range in four cases above-mentioned through linear regression analysis of finite element results by using data-analysis software ORIGIN.