Study On Geometrical Nonlinearity And Shear Lag Effect In Flat Steel Box Girder Of Large Span Steel Arch Bridge

The development of steel arch bridge, the present researches on static analysis of large span arch bridge considering the effect of geometrical nonlinearity, and the present researches on shear lag effects in box girder at home and abroad were summarized. Based on Mingzhou Bridge in Ningbo, which is a half-through tied arch bridge with steel box arch-ribs and the main span of which is 450m, the effect of geometrical nonlinearity on static analysis, the shear lag effect in flat steel box girder of the side span and the parameter analysis of the shear lag effect in flat steel box girder were studied respectively.The whole bridge beam element model of Mingzhou Bridge was built to study the static analysis of the construction stage and completion stage. By the results, it can be concluded that considering the stayed-cable effect, "beam column effect" and large displacement effect during the construction stage, the geometrical nonlinearity influence coefficient for structural displacement is about 5%, for internal forces is about 10%. And considering the horizontal tie and suspender effect, "beam column effect" and large displacement effect during the completion stage, the geometrical nonlinearity influence coefficient for structural displacement is about 5%, for internal forces is about 10%. Therefore, it is suggested that the influence of geometrical nonlinearity should be considered during the calculation of large span steel arch bridge.The beam shell hybrid element model of the side span of Mingzhou Bridge was built to study the shear lag effect in flat steel box girder. Based on the results, the following conclusions were obtained. The shear lag effect made the distribution of bending normal stresses uneven, as a result, the stiffness of the section is reduced, and the whole stiffness of side span of Mingzhou Bridge is reduced. Owing to this, the result of bending moment on the leg arch increased 30% than the result calculated by the beam element model. Meanwhile, the results of vertical deflection of the leg arch and the flat steel box girder also increased 30% than the results calculated by the beam element model. Furthermore, the bending normal stress was 2.8 times larger than the results obtained by beam element model of full effective section at most. Therefore,, it is suggested that the local shell element model of flat steel box girder should be built to calculate the stress during the design and construction process of large span steel arch bridge, and during the overall calculation of large span steel arch bridge, some decrease of the stiffness of section of the flat steel box girder should be considered.On the basis of the flat steel box girder of Mingzhou Bridge, the parameter analysis was carried out from the point of effective width coefficient. The results showed that the influence of the width to span ratio is the most remarkable on the shear lag effect and the influence of the thickness of longitudinal partition is significant, the influence of the width to height ratio and the thickness of top and bottom plate is small, the influence of the thickness and space of transverse partition is also very small.