Research On Overall Stability About The Simply Supported I-section Steel Beams Under Combined Bending And Torsion

Because of its good features of structure and mechanical properties, I-sectionsteel beam is widely used in the modern architectural engineering. Being of highstrength and light weight determines that the limit bearing capacity of the steelstructural element is controlled by the stability of the elements rather than the strength.As for the stability of opening section members, a great deal of research has beenconducted both at home and abroad and successes have been achieved. However, theresearches on the overall stability of I-shaped cross-section beams under bending andtorsion are relatively few, while the problem extensively exists in engineering, andthere is no verification formula in the current Code for Design of Steel Structures(GB50017-2003) either, thus, it is necessary to conduct in-depth studies anddiscussions on this project.Starting with traditional theory of overall stability of steel I-beam, the thesisintroduces the the balanced differential equation and the total potential energyequation by using the balance method and energy method. Since it is hard to get theanalytic solution of these equation, it is needed to use numerical analysis methodwhen studies the overall stability of the steel I-beam under bending and torsion. Thenthe thesis elaborate the basic concept of finite element analysis and the calculationmethod and procedures of overall stability bearing capacity of steel I-beam underbending and torsion by using finite element analysis. Finally, a critierion is gived todetermind the state of overall stability and the ultimate overall stability bearingcapacity of steel I-beam.By using the finite element software ANSYS, the thesis did non-linear bucklinganalysis on the overall stability of the steel I-beam under bending and torsion. Whenanalyzing, the influences of section parameters, such as eccentricity, span of the steelbeam, the height of web and the width of flange are mainly taken into consideration.Meanwhile, considering influences of different parameters, the overall stability limitload of the steel steam under bending and torsion is obtained. After this, the changerule of deformation characteristic curves along with the changes of these factors issummarized. According to the analysis results, the thesis makes comparative analysisof the various I-section steel beams’ bending-tensional related curve model.Considering all the analysis results above, the thesis obtains the influence factors α, β andγ’s formula in assumed fitting equation based on Trahair formula throughregression analysis of finite element results by using the data analysis softwareORIGIN. Thereby, the ultimate bearing capacity formula for overall stability capacityof steel I-beam under bending and to rsion is obtained. Finally, it compares with theANSYS result and verifies the applicability of the proposed formula after analysis.