The Study On Mechanical Performance And Structural Optimization Of Steel Truss-concrete Composite Section For Hybrid Girder Cable-stayed Bridge

The cable-stayed bridges with steel truss-concrete hybrid girder have been gradually applied in highway,railway,and both of them in recent years,because of its excellent mechanical performances.However,the research concerning the bridge type is far from enough.With a rough reference to structural principle of ordinary steel-concrete composite section,stiffness and effective section of the composite section are often significantly larger than those of sideward main beams,which results in excessive design on safety.Therefore,it is of great importance to optimize the composite section on the basis of consistency of stiffness,smooth transmission of force and deformation coordination of the main beam.The mechanical behavior,stiffness matching and deformation characteristics of steel truss-concrete composite section have been experimentally and numerically investigated in this thesis.A structural optimization scheme is proposed according to the structural features of steel truss-concrete composite section.The main research work and outcomes are as follows:(1)A static model test has been carried out.The results demonstrate that stresses of all test points tend to be small under the design load condition,with a uniform distribution and smooth transition.Most of stress values can meet the limit requirements of the code,except that stress values of test points near prestressed concrete beam and the connecting part between the concrete beam and bearing slab are relatively high.The whole structure is in the compression state.All stress-load curves are basically linear under 1.6 times' design load condition.The vertical displacements of the test points near the composite section are very small and consistent.The welded shear studs on both roof and bottom of the composite section and bearing plate are completely in elastic state.All stress values are small.The steel truss-concrete composite section shows good mechanical behavior during the entire test.(2)Numerical analysis of steel truss-concrete composite section has been conducted,and the results validate the experiment mentioned before.The whole structure presents similar structural behavior and mechanical characteristics.In addition,1.7 times design load condition are researched.In general,the measured stress values are generally smaller than the calculated ones while trend of the former is consistent with the latter.Therefore,it's safe and feasible to design the bridge according to the calculated stress values.(3)An optimized structure design has been proposed,namely canceling the solid section,removing the welded shear studs of both roof and bottom plate and increasing thickness of the bearing plate.This kind of structure can greatly lower the change of stiffness and centroid position of the main beam caused by the solid section,thereby facilitating the construction.The numerical analysis result shows that the stress distribution is uniform and the transition is smooth under the design load condition.There is no obvious abrupt stress at the connecting part between the steel box transition section and the bearing plate.The deformation of steel truss beam and concrete box girder are very small.The stiffness of the structure is big enough and the deformation is in consistency.The research indicates that the optimized structure design is safe and feasible,which can be applied to bridges of the same type.