| The self-anchored cable-stayed suspension system bridge combines self-anchored suspension bridge and cable-stayed bridge.It shows excellent structural performance,good economic benefits,large social development requirements and has significant advantages in the construction of long-span bridges.With complex force mechanism,structural responses of the self-anchored cable-stayed suspension system bridges are sensitive to design parameters adjustments,many problems in design and calculation are urgently needed to be solved.This paper was carried out on the basis of a self-anchored cable-stayed suspension system bridge-Ningbo Changhong Bridge with a main span of 420m.This article focused on the following aspects of research of the self-anchored cooperative system bridges:simplified analysis calculation,design parameters analysis,internal forces in the transition section and the research of cross suspender cables number:(1)Based on the elastic foundation beam method and response surface method and energy principle,a simplified calculation model suitable for the preliminary design phase of the self-anchored cable-stayed-suspended system bridges is proposed to calculate structural responses under vertical uniform load.This method simplifies the cooperative system into an elastically supported continuous beam,with converting the supporting intensity of the tower and cable into the stiffness of the elastic foundation.On the basic of the elastic foundation beam,the basic formulas of beam deflection and bending moments are derived and have been validated that are applicable for the long-span self-anchor cable-stayed-suspension bridges with 400?800m main span.(2)Under the background of Ningbo Changhong Bridge,the response surface method is used to analyze the influence of the material parameters and geometric parameters on the static performance of the cooperative system bridge.The research results show that:the increase in the tensile stiffness of the stay cable will increase the proportion of the load allocated to the cable-stayed system,which will greatly change the local stress of the structure,but have little effect on the overall structural force.The main cable tensile stiffness is the most sensitive parameter for the mid-span deflection and mid-span bending moment of the stiffening beam,as well as the tower root bending moment and the tower top level.The coupling effect of geometric parameters and stiffness parameters is often greater than that of two single parameter adjustments,so when the single variable adjustment cannot meet the structural stress and deformation requirements,the parameter value of the coupling term can be adjusted.(3)The applicability of the simplified model of the foundation beam to the analysis of the dynamic problems is explored.The finite element model is combined with the response surface method to establish a response surface model,which could be used to analyze how the changes in main design parameters affect the natural frequency and modes of the self-anchored cable-stayed suspension bridge.The research results show that:The increase of the main cable tensile stiffness has a positive improve in the three-way stiffness of the system and the its promotion efficiency is higher than the vector-span ratio and the oblique-span ratio.Among the four main design parameters,the tensile stiffness of the stay cable is the most sensitive parameter of the dynamic characteristics of the cooperative system,and the influence of the four parameters on the first?second and third natural frequencies are all weakened in turn.Adjusting the structural geometric parameters and material parameters at the same time can more effectively regulate the overall stiffness of the system to achieve the design state.(4)Through establishing the finite element model of the transition section,the force state and the effects of crossed suspender cables' number on the static and dynamic performance of the system are studied.The research results show that:the installation of crossed suspender cables can significantly reduce the main beam displacement and the stress amplitude of the cables.But the number of crossed suspender cables has little effect on the natural vibration characteristics.The difference of the suspension joints' anchor positions has a great impact on the displacement of the main beam,and considering the sag effect of long stay cables,it is reasonable to distribute the crossed suspender cables symmetrically at the center anchoring position-0.3L of the stiffening beam.As the number of cross slings increases,the geometric stability of the structure is improved and the stiffness distribution becomes more uniform,the stress amplitude curve and live load effect ration curve of stay cable are also smoother. |
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