Research And Analysis On The Second Systym Of Composite Beams With Wide Deck

Cable stayed bridge with wide breadth composite beam and PK section is a typical form of long-span Bridges.Compared with the steel cable-stayed bridge,the bridge not only possesses the characteristics of large stiffness,good wind resistance stability,also can avoid the fatigue problems of orthotropic steel deck.The middle span of the Cable stayed bridge is composite beam with wide deck.As for the analysis of composite beams with wide deck,finite element analysis is more likely to be adopted,the process of building model and calculation is complicated and time-consuming.The paper adopts the combination of theoretical derivation and finite element method,stress and deformation calculation method of the second system in composite girder cable-stayed bridge is studied.To be specific,the thesis mainly done the following work:(1)The simplified calculation of the stress of the simply supported composite beam and cantilever composite beam is analyzed by using the method of three three bar simulation analysis method.First of all,according to the principle of equal stress,the composite beam is compared to the analysis model with the stiffening bar that only bears the axial force and the tie plate that only bears the shear force.Then,the differential equations are established according to the static equilibrium condition and deformation compatibility condition between the stiffening bar and the tie plate.Stress calculation formula of concrete flange of the second system is derived according to the boundary conditions and loading conditions.Finally calculation formula of concrete flange width is obtained according to the definition.(2)Composite beam with wide deck is divided into three systems.The first system is composed of the box girder and the concrete slab,and the second system is composed of cross beam and the concrete slab.The third system is the concrete bridge deck supported on the beam.Then,the boundary conditions and internal forces of the second system are analyzed,and the calculation formula of the internal force of the second system under load is obtained.An method is presented to calculate the flexural stiffness of the second system simplified mechanical model.According to the zero-moment point,the second system is devided into equivalent beam and equivalent cantilever beam.(3)The simplified calculation of the deflection of the second system is analyzed by using the method of the energy variational method.First of all,the cubic parabola is selected as the reasonable mode of longitudinal warping displacement,next shear lag warping displacement and deflection is selected as the two generalized displacements to calculate the total potential energy of the structure,and then in accordance with the principle of minimum potential energy,control differential equations and natural boundary conditions are obtained,coefficients and deflection formula are deduced by the boundary conditions and load conditions.At last,the equivalent length of cantilever is modified and the deflection formula is improved considering the influence of shear deformation on deflection.(4)Based on the finite element method,the finite element model is established by using the finite element software ANSYS.The deflection and stress of the second system under uniform load and concentrated load are analyzed.The detailed calculation process of the simplified calculation method for the stress and deflection of the second system is provided.Finally,compared the result of simplified calculation method and the result of finite element method,and the applicability and accuracy of the simplified calculation formula of stress and deflection of the second system are illustrated.