Research On The Static And Dynamic Characteristics And Torsional Effect Of Long-span Suspension Bridges With Spatial Cable System

Since the 21st century,the construction of space cable suspension bridges has been in the ascendant all over the world.Because of the smooth and graceful alignment of space cable suspension bridges and the inclination of suspension cables,in static aspects,the lateral bearing capacity of cable systems has been greatly improved with little influence on the vertical bearing capacity;In dynamic aspect,inclined suspension increases the restraint of cable to stiffening beam,effectively restrains the "pendulum effect" of stiffening beam,improves the overall torsional stiffness of the structure,and improves the aerodynamic stability of the structure.Therefore,large-span spatial cable suspension bridges are increasingly appearing in people's vision.However,there are few space cable suspension bridges built at home and abroad,and most of them are self-anchored suspension bridges with small span.This shows that the static and dynamic characteristics of long-span spatial cable suspension bridges are not well understood.There are still many problems to be solved if this type of bridge is really to be popularized in large-span and strong typhoon areas.In view of the above problems,this paper relies on Baotaping Bridge,a long-span space cable suspension bridge with spatial cable system,to study the static and dynamic characteristics of space cables in different structural forms.The main contents of this paper are as follows:Firstly,the reasonable completion state of space cable suspension bridge is determined by using the revised iteration algorithm and the three-dimensional non-linear analysis software BNLAS.The formulas for calculating the lateral deflection angle of self-anchored and ground-anchored spatial cable suspension bridges are derived.The effects of different stiffening girder erection schemes and lateral bracing schemes on the lateral deflection angle of suspension cables,the lateral inclination angle of suspension cables and the internal force of supporting rods are compared and analyzed.The mechanism that the cross bracing method between cables is beneficial to the structural system transformation is revealed.The results show that the method of cross bracing between cables provides rigid support for the main cable,which makes the transverse alignment of the main cable close to the bridge alignment when the top bracing is completed,and greatly improves the conversion efficiency of the system.In addition,the more crosswise supporting points,the smaller the crosswise deviation angle of the sling,the easier the installation of the sling.Secondly,based on the key design parameters of space cable suspension bridge,the effects of the lateral sagittal ratio,vertical sagittal ratio,bridge tower,main cable and stiffening beam stiffness on the static characteristics of space cable are summarized.The results show that increasing the lateral sagittal ratio can significantly increase the transverse stiffness of the structure,and reducing the vertical sagittal ratio is the most effective measure to increase the vertical stiffness of the structure.Thirdly,the effects of different central buckling modes on the static and dynamic characteristics of structures are studied,and the dynamic characteristics and torsion-bending frequency ratios of structures under different structural forms and different central buckling modes are compared and analyzed,and the priority order of flutter instability of structures is summarized.It is concluded that the longitudinal and torsional stiffness of the structure can be significantly increased by the central buckle.Finally,through the analysis of torsion effect of main cable of space cable suspension bridge,the influence of torsion stiffness and lateral deviation angle of cable clamp on torsion angle and torsion secondary internal force of main cable is comparatively studied,and the variation law of torsion effect of main cable in the whole construction process of different construction methods is analyzed.The results show that the torsional stiffness of the main cable has little influence on the torsional effect.The larger the lateral deviation angle of the clamp,the greater the secondary torsional internal force of the main cable.When different construction schemes are adopted,the maximum secondary internal force always appears on the cable section near the side of the tower.