Research Of Torque Effect On The Overall Stability Of Simply Supported I-section Steel Beam

Steel has the advantages of high strength, light weight and good mechanicalproperties, so it is an excellent building material of construction structures. Becauseof these characteristics of steel, the limit bearing capacity of the steel structuralelement tends to be controlled by the stability of the elements other than the strengthof the material. For the elements encounter instability failure before the materialoccurs strength failure. Domestic and foreign scholars have carried out a large numberof theoretical studies and experimental works on the overall stability of the opensection thin-walled components, and have achieved fruitful research results; however,the researches on the overall stability of steel beams under lateral eccentric loads arerelatively few, while the problem extensively exists in engineering, and there is noverification formula in the current “Design of Steel Structures”(GB50017-2003)either, thus, it is necessary to conduct in-depth studies and discussions on this project.Starting with the basic stability theory of steel structure, the thesis introduces thetraditional theory of overall stability of steel I-beam. Based on this theory, ittheoretically studies on steel I-beam stability under lateral eccentric loads and endmoments, and lists the balanced differential equation and the total potential energyequation by using the balance method and energy method. Then, based on a series ofassumptions, it gets a bending-torsion correlation equation in this case of eccentricconcentrated load with a system of inhomogeneous equations from Rayleigh-Ritzmethod, which contains two undetermined parameters. Since it is hardly to get theanalytic solution of this equation, the thesis draws lessons from the form of theLindner formula and the overall stability calculation formula for load deviated fromshear center of the bending element but paralleled with the main shaft in “TechnicalCode of Cold-formed Thin-wall Steel Structures”(GB50018-2002) of China, andintroduces a torque influence factor kωto adjust the influence of warping stress forrestraining torsion generation on overall stability bearing capacity of steel I-beam.Accordingly, it puts forward the verification formula for overall stability capacity ofsteel I-beam while the influence of torque is taken into consideration.By using the finite element software ANSYS to do non-linear buckling analysison the overall stability of the steel I-beam under eccentric concentrated loads, thethesis gets the limit bearing capacity of the steel I-beam. During analyzing, the influences of section parameters, such as eccentricity e, span of the steel beam l,the compression flange widthb1, are mainly taken into consideration. And then, theoverall stability limit load of the steel steam under eccentric concentrated load withconsideration of influences of different parameters is obtained and the kωwithdifferent values are worked out. According to the results, the thesis analyzes theinfluence of the section parameters, such as eccentricity e, span of the steel beam land the compression flange widthb1, on the overall stability limit load of the steelbeam and the variation rules of torque influence factor kωaccording to theparameter variation. Those influence parameters are applied with dimensionlessmethod byT/T0. Torque influence factor kωand dimensionless variableT/T0areapplied with regression analyses through the data analysis software ORIGIN, and thenumeric calculation formula for torque influence factor kωis obtained. Thereby, theverification formula for overall stability capacity of steel I-beam under eccentricconcentrated loads is obtained. Finally, it compares with the Lindner formula and thetest results, and verifies the applicability of the proposed formula in this thesis afteranalysis.