Research On Space Mechanical Properties Of Wide Separated Steel Box Girder Of Cable-Stayed-Suspension System Bridge

With the increasing traffic flow and the rapid development of high-speed railway in China,bridges,as an important part of the railway,have developed rapidly,and long-span bridges have begun to rise in China.In order to meet the development trend of larger span and wider deck of modern bridge,wide split steel box girder arises at the historic moment.The wide split steel box girder not only includes all the advantages of the steel box girder,but also has more advantages in wind stability and reducing the dead weight of the structure.At the same time,the problem brought by the wide split steel box girder is that the mechanical behavior is more complex.The steel box girder is subjected to a common force through the crossbeam,and the structure has obvious spatial stress characteristics under different loads in different construction stages,which makes the conventional member bending theory and torsion theory based on the assumption of peripheral rigidity no longer applicable.Mechanical behaviors such as bi-directional bending,constrained torsion and shear lag are worthy of attention.In this paper,taking the Xihoumen Highway and Railway Bridge of Yongzhou Railway as the background,and taking the main girder of the cable-stayed suspension section as the research object,the longitudinal and transverse shear lag effect and torsion effect of wide split steel box girder are studied by establishing the whole bridge bar model and local beam model.The main contents of this thesis are as follows:(1)Considering the four symmetrical load conditions of the bridge,the top and bottom of the railway box show obvious negative shear lag,the maximum shear lag coefficient is not higher than 1.2,the position of the highway box far from the cable force is positive shear lag effect,and the maximum connection position of the crossbeam is 1.3.For the railway box girder,increasing the thickness of the web should significantly reduce the shear lag effect of the bottom plate,while the increase of the width of the crossbeam can effectively improve the longitudinal shear lag of the top and bottom,and the transverse position of the sling has little effect on it.Based on the analysis of the influence of the axial component of the stay cable on the stress of the box girder,it is found that the non-uniform stress gradually disappears after0.75 times the width of the bridge.(2)The transverse shear lag effect under four symmetrical load conditions of the bridge is analyzed.The plate and shell model is longitudinally equivalent to a T-shaped beam with the cross beam and the corresponding partition as the web.It is calculated that the stress at the position of the crossbeam changes significantly and the transverse shear lag effect is obvious.Reducing the thickness of the web and increasing the width of the crossbeam can effectively reduce the transverse shear lag effect,and the transverse position of the sling has little influence on it.The internal force of the statically indeterminate frame with elastic support on four transverse cable planes is analyzed,and the stiffness ratio relationship between slings and stay cables when the internal force is optimal is derived.(3)Considering the three kinds of eccentric loads in the bridge state,three typical cross sections of the wide split steel box girder are selected to study the torsional effect.The results show that the torsional effect of the cross section without beam is the most obvious under the same load.The torsion effect can be reduced by increasing the thickness of the web and choosing the width of the beam reasonably,while the transverse distance of the sling has little influence on the torsion effect.