Study On Mechanical Behavior Of Concrete Wide Box Girder Of Single Tower Cable - Stayed Bridge

The flange plates of the broad box girder are wide, so there is shear lag phenomenon in the flap, making longitudinal normal stress along the lateral distribution of the box girder non-uniform. This is called shear lag effect. If the effect of shear lag effect was ignored in design and construction, the concrete crack may appear due to stress concentration in the wide box girders made of concrete. Therefore, it is necessary to research the shear lag effect of broad box girder. The force characteristics of concrete broad box girder and the shear lag effect of broad box girder were analyzed in this paper. And the single tower cable-stayed bridge in Liu-he district of Nanjing was taken as an engineering example.Firstly, the theories and methods on the research of shear lag effect were summarized in this paper. The corresponding bridge FEM model had been constructed with spatial beam elements by using’ Midas/Civil software. Then the internal forces and stress distribution under some critical states were obtained through structural stress analyses. The main decking system of the bridge could meet the standard requirements of the capacity limit state and the serviceability limit state. The bending moments of the main span were mostly influenced by the cable, while the side spans were mainly affected by the moving loads in the ultimate limit state.Secondly, the FEM model of the cable-stayed bridge with solid element had been further constructed using Midas/FEA software.Under the loading case of mere dead load, shear lag effect of main beam was analyzed by longitudinal normal stress and shear lag coefficient curve illustration of the main typical cross section was charted. The shear lag effect of main girder of cable-stayed bridge made the longitudinal normal stress non-uniform along the cross section. The shear lag effect of variable section relative to the general section was stronger. The shear lag effect of the variable cross-section bottom slabs was mostly influenced by the cable, and it decreased with the increase of the distance of cables gradually. The shear lag effects of distribution law were similar in main span and side span, but the shear lag effect in side span was slightly stronger than in main span.Lastly, parameterized finite element models were established by Midas/FEA. There were several factors on the shear lag effect, such as the thickness of diaphragm plate, the layout space of diaphragm plate, the chamfer, the thickness of slab, the thickness of the bottom flange, the longitudinal initial stress and the concrete strength. Increasing the thickness of diaphragm plate, roof and floor, reducing the interval of diaphragm plate and increasing the chamfer could reduce the shear lag effect of the roof of box beam. The chancre of thickness in bottom plate had little effect on the shear lag effect of box girder. The changes of above parameters had small influence on shear lag effect of wide box girder. Longitudinal initial stress reduced the shear lag effect of box girder in cable-stayed bridge, which was favorable for the structure.But with the increase of initial stress, the change of shear lag coefficient amplitude decreased. The changing of the strength of concrete almost had no influence on the shear lag effect of wide box girder in cable-stayed bridge.The stress characteristic of the single tower cable-stayed bridge with concrete broad box girder was researched in this paper. And this paper might be a certain reference to design and construction of similar tower cable-stayed bridge with concrete broad box girder.