Study On Overall Stability Of Simply Supported I-section Steel Beam With Two Lateral Bracing For Its Compression Flange

When loading reaches a certain limits, compression flange of a girder deformslaterally, arousing lateral movement at webs and tensile flange, which generates arelative reverse angle of the whole section. So at this time it is said that the girder, themain component of steel structure, has flexural-torsional buckling. Steel structuredesign shall guarantee overall stability of structure and components while settinglateral bracing for compression flange is an effective measure to improve thestructural stability. Code for Design of Steel Structures (GB50017-2003) onlyprovides calculation method for setting equidistant lateral bracings for girders, and asfor mutual constraints between beam sections, it adopts increase of equivalentmoment coefficientβ bto indicate decrease of effective length of dangerous beamsection, which is not convenient for designers to rapidly understand the truth.Moreover, the code does not provide calculation method for setting non-equidistantlateral bracings for girders. Therefore, research on calculation method for overallstability of these girders has significant theoretical and practical value.The thesis, which has a systematic study on the overall stability of dual axlesymmetric I-section beam with two lateral bracing for its compression flange,includes four parts, namely, theoretical deducing, finite element analysis, comparativeanalysis of the result and regression analysis.(1) Theoretical deducing. First, inaccordance with the energy method theory, the thesis, taking middle section intoconsideration independently, deduces the critical moment of girder’s overall stabilityunder four different load types. Next, the thesis introduces the calculation methodwhich considers mutual constraint effect of beam sections proposed by Nethercot andTrahair (hereinafter referred to as "NT method").(2) Finite element analysis. Thethesis, mainly adopting ANSYS finite element analysis software, carries outeigenvalue buckling analysis on192girders considering the lateral bracing conditionsand changes of cross section shape and type of simply supported steel beam with totalspan15m.(3) Comparative analysis of the result. Considering changes of absoluteerrors between the three methods (energy method,“NT method”, and finite elementmethod), the thesis carries out comparative analysis on the critical load of overallstability calculated by the three methods, through which the author evaluates theaccuracy and practical applicability of the two theoretical approaches.(4) Regression analysis. The thesis, employing Origin regression analysis software, fits the formulafor equivalent moment coefficientβ bof girders under different load types, i.e. fullcross uniformly distributed load function, midspan concentrated load and supportingplace concentrated load, and successfully draws the relation curve between equivalentmoment coefficientβ band span ratio ξ. Each load case obtains the computationalformula ofβ b.