Study On Influence Of Different Loading Pattern On Shear Lag Effect Of Twin-cell Box Girder

With the development of economy in China, the use of box girder is more extensive, andthe cantilever of the box girder is longer, the flange is more widened. Especially the boxgirder is used in the construction of long-span bridges is more common, in the progressivedevelopment and practice of the box girder, designers found that results calculated byelementary beam theory had been unable to meet the actual stress state. underefforts,researchers found that shear lag caused distribution of stress uneven, and inengineering practice, many phenomenon destoried by the shear lag is found, this caused theattention of the researchers, and conducted a lot of research work that made the box girderstress more in line with the actual stress state. In this paper, taking the single box double roomrectangular box girder as an example, studying different modes of loading influences on theshear lag effect of box girder, through theory and finite element numerical calculationmethods, comparing the two calculation results, and summarising the different rules, mainlyfrom the following aspects to study.In the theoretical calculation, analyzing the stress mechanism of single box double roomrectangular box girder, derived formula of box girder section of the shear lag coefficient anddeflection of the double box girder under simply supported and cantilevethe boundaryconditions in the effect of different loading mode by energy variational principle.In theseformula, the additional stress and deflection of a part of the elementary beam theory tocalculate and shear lag effect.In the calculation of finite element, In this paper, Using Midas/FEA to simulate thedouble chamber beam of rectangular section, and compared the calculated results with thetheoretical results to verify the reliability of the box girder normal stress by Midas/FEAsoftware, the two calculation methods can satisfy the safety of structure.Different boundary conditions and loading mode influences on the shear lag effect ofbox girder is different，slecting the simply supported and cantilever boundary conditions,applying concentrated load and uniform load in the tiwn-cell box girder, and considering threeload conditions of each load. Using the finite element software to establish the structuralmodel under different boundary conditions and loading conditions. Calculating the normalstress of cross section values and compared with the results calculated by the elementarybeam theory, The result is the box beam shear lag coefficient. Analyzing and summarizing theshear lag coefficient, suming up the impact of different loading modes on the shear lag effectof box beam, the transverse distribution of the normal stress of sections, finding the mostunfavorable point and the worst load cases of the dangerous section of the box girder as thecontrol point of structure design. Select the span of double chamber rectangular box beam with40m as engineeringbackground, to establish the finite element model of box girder bridge with MIDAS/FEAfinite element program, analysis of the transverse distribution of normal stress and deflectionunder different loads of simply supported, cantilever beam pattern.