Study On The Span Limiting Factors And Reasonable Structural Parameters Of Cable-stayed Bridge Without Back Cable

The cable-stayed bridge without back cable-stayed bridge is novel in structure and beautiful in appearance.With the continuous development of society,people have been increasing the span requirements of bridges.Therefore,it is necessary to study the span limiting factors and reasonable structural parameters of cable-stayed bridges without back cables,explore the extreme span of cable-stayed bridges without back cables in the reasonable structural parameters,and broaden the scope of application of such bridges.In this paper,the paper studies the span limiting factors and reasonable structural parameters of a cable-stayed bridge without back cables in Gansu Province as the engineering background.(1)Based on the load balance theory and the cable membrane assumption,considering the inclined tower angle factor,the analytical formulas of the main girder axial force under various cable surface arrangements are derived,and compared with other methods.Based on the static analysis of single cable,the deformation coordination equation of cable element is derived.The cubic interpolation function of cable deflection curve equation is obtained by weighted residual value method,and the function of cable force and deflection of main beam is established.(2)The main factors influencing span are the axial force,cable strength,deflection and buckling stability of the main beam.The following work is done:(1)the expression of axial force extreme span of main beam is derived,and the span growth curve dominated by area and allowable stress is obtained;(2)The strength extreme span expressions of cables under the condition of considering the sag effect and the non sag effect are derived,and the span trend diagram under the influence of cable strength is obtained;(3)Based on the equivalent elastic foundation beam theory,the deflection extreme span expression of the main beam is derived.The span is gradually increased by increasing the length of the cable free zone and the distance between cables.Combined with the limit value of the ratio of deflection span specified in material mechanics,the allowable deflection range under different span is obtained,and the span deflection trend diagram is formed;(4)Based on the theory of elastic foundation beam and the stability theory of compression bar,the equivalent foundation coefficient at the quarter of the main beam considering the inclined tower inclination is deduced.The formula of the buckling stability in and out of plane of the main beam is further deduced.The relationship between the stability of the main beam and the span is obtained.On this basis,the relationship between the ultimate span and the instability of the main beam is studied.(3)This paper chooses inclined tower angle,high span ratio,girder cable spacing and beam tower stiffness ratio as the main research objects.Through the finite element model analysis,the reasonable structural parameters of cable-stayed bridge without back cable are explored.By controlling variable method,the inclination,high span ratio,cable spacing of main girder and stiffness ratio of girder and tower are changed respectively.Through finite element calculation,the internal force and deformation data under different parameter models are obtained,including the cable force of bridge forming,stress of main beam,bending moment and deflection of main beam,bending moment and deflection of inclined tower and displacement along the bridge,etc.,forming the internal force and deformation trend diagram under single parameter change,and summarizing through induction,The reasonable structure parameters range is obtained.The conclusion includes: the reasonable inclination range of inclined tower is 54 °～ seventy-six °;The reasonable height span ratio is generally controlled between 0.5 and 0.7;When the ratio of height to span is between 0.5 and 0.7,the ratio between reasonable cable spacing and beam length is between 0.09-0.15.The study of span limit factors and reasonable structural parameters of cable-stayed bridge without back cable-stayed bridge is of great significance to broaden the scope of application of the bridge type,and provide some reference for the design of this type of bridge in the future.