Overall Stability Research Of Fixed-ends Steel I-Beams

The characteristics of steel determine the bearing capacity of the steel structure,which is not controlled by the strength of materials, but by the stability, including theintegral stability as the core content. The researches of the overall steel beam stabilityproblems have achieved fruitful achievements at home and abroad. In recent years,the steel structure system in China has made significant progress, but there is yet to beimproved. In the actual project, most of the steel beams are simplified for the simplysupported beam to be calculated. Although this calculation is relatively safe, and verysimple, for the fixed ends beam of practical engineering, this approach is tooconservative and not economic. There are only design formulas for calculating thebearing capacity of the overall stability of simply supported steel I-beams andcantilever steel I-beams under lateral load in Code for design of steel structures (GB50017-2003) also. Therefore, it is necessary to carry on the research to solve thisproblem, and strive to get an applicable and succinct formula that can be used forengineering design, so as to provide reference in next revision on Code for design ofsteel structures. Taking into account the nodes of the frame beam stiffness and nodaldisplacements, this thesis assumes that joint stiffness is large enough. Thus, the steelframe beams will be simplified to fixed-ends beam.Firstly this thesis introduced and compared several different present overallstability theories, and pointed out some shortcomings of them, and then, reached theconclusion that the traditional theory result was correct. On this basis, the thesisdeduced a formula for the calculation of the bearing capacity of the overall stability offixed-ends steel I-beams by energy method. Referencing Code for design of steelstructures (GB50017-2003), the thesis deduced a new equivalent bending momentcoefficientβ bby energy method. In order to facilitate the engineering design, thethesis made the fixed-ends beam and the simply supported beam to have the sameform of the formulas.This thesis analyses various components by finite element software ANSYS. Theelement SHELL181is used in the analysis. Then it compared the calculated data withthe results of the new formulas, and verified the derived formulas as correct. Thisthesis analyses the influence factors of the overall stability of the fixed-ends steelI-beam, and finds out the rule, and then analyses the two important factorsβ b＆ξ.Furthermore, it had some important conclusions. Based on this, by using of the data analysis software ORIGIN, the thesis analyzes finite element analysis results byregression analysis. At last, the thesis reaches simple formulas that can be used forengineering calculations, and illustrated the scope of application. On the basis ofexisting theory, considering the impact of geometric nonlinearity and materialnonlinearity, this thesis presents the elastic-plastic approximation correction formulaof overall stability factor in non-elastic phase. In order to verify the applicability ofthe formulas, the thesis compared the calculation results of new formulas withANSI/AISC360-05.