Study On Influence Of Different Loading Methods On Shear Lag Effect Of Thin-walled Box Girder

Application of box girder in the construction of contemporary bridge is more and morewidely, and the structural form of single chamber, large cantilever, wide flange and thin wallbecomes the trend of development. By many years’ application, shear lag problems of boxgirder are found and studied, research work has achieved some results, solved some practicalproblems, but there are still some problems which are not well solved, and further analysisand demonstration are needed for. An important starting point of study on the shear lag effectof box girder, is to choose the factors which have some influence on shear lag effect and givesome systematic study on. The objective is not only to find the changes happened or the trendof changes, but also to know how these factors to affect the shear lag effect of box girder andeven the degree of influence. According to the influence law of these factors which may affectthe shear lag effect of box girder, some measures can be carried out to reduce the bad effects,and the design conception also can be promoted to produce more advanced design project. Inthis paper, the single box girder with single room and thin-walled is focused on, the analysiscontains not only the shear lag effect of simply supported and cantilever box girder, but alsothe influence of different loading methods on shear lag effect of thin-walled box girder. Themain studies are as follows.According to the deformation characteristics of single box girder with single room andthin-walled, when it is under load and shear lag effect is considered, selecting cubic parabolaas shear lag warping displacement mode, using the principle of minimum potential energywhich is based on energy variation method, the formula can be obtained:the Shear lagcoefficient expressions of box girder section due to different boundary conditions anddifferent loading modes,the corrected expressions of deflection influenced by the shear legeffect of box girder.As a contrast, Some particular thin-walled box girder structures are analyzed through theANSYS software, and the results are very close to these calculated by above formulas whichare given in this paper. So it is indicated that these two types of different solving methods areall right and can be trusted.This paper is focused on the influence of different loading methods on shear lag effect ofthin-walled box girder. According to the finite element method, this paper selects simplysupported and cantilever box girder as the objects of study. There are two kinds of differentload types, concentrated load and uniformly distributed load. At the same time each load typecan be divided into five different loading methods. Through a series of calculation andanalysis, such results can be gained: the shear lag coefficients of the key points at the mostdangerous section; the normal stress’s change regulation at the key section; and the greatest normal stress caused by the most risky load method at the key section. So it can be found thatwhich one is the most risky load method. There also tries to give the reason why some loadmethods may cause greater shear lag coefficients and what is the key factor for theseconditions, the direct answer is like this: the distance between the load and the key point mayhave something to do with the shear lag effect. If the load is exerted closer to the points whichare focused on at the section, then stress concentration becomes more serious at these places.It can be indicated that the different loading methods needs to be specially discussed towardssome specific questions of shear lag effect of box girder.