Study Of Dynamic Characteristics And Aerostatic Stability For Partially Ground-anchored Cable-stayed Bridges With Rigid Hinge

The partially ground-anchored cable-stayed bridge with rigid hinges is one of the the new types of long-span and complex bridge structures.The integral stiffness and stress state of this type of bridge are different from those of ordinary cable-stayed bridges due to the ground-anchored cables and rigid hinges.The importance of the study of aerostatic stability for this type of bridge can not be ignored.Considering a cable-stayed bridge with rigid hinges,this paper studies its dynamic characteristics and aerostatic stability by using finite element analysis software ANSYS.Through the analysis of dynamic characteristics,We calculated the corresponding frequencies and modes of the free vibration of this structure,which will be helpful for the further linear analysis of aerostatic stability and flutter analysis.Based on the modified internal and external double iteration method and APDL language provided by ANSYS,this paper compiles a non-linear analysis program of aerostatic stability,analyses and studies the whole process of aerostatic instability of the bridge,and further explores the mechanism of aerostatic instability,and analyses the influence of various parameters on structural aerostatic stability.This paper carries out the following research contents and the corresponding conclusions:(1)The basic theory of dynamic characteristic analysis and aerostatic stability analysis is introduced,the main non-linear factors affecting aerostatic stability are expounded,the criteria for determining aerostatic instability are given,and the non-linear analysis method of aerostatic stability is introduced in detail.(2)The finite element model of the whole bridge is established by using finite element analysis software ANSYS and MIDAS respectively,and the modal analysis is carried out by using Lanczos vector iteration method.We calculated the frequency and mode shapes of the first 20 natural modes of the bridge,as well as the corresponding equivalent modal quality and the equivalent mass inertia moment.It is concluded that rigid hinges have less influence on torsional modes and greater influence on vertical and lateral bending modes.(3)The program of non-linear analysis of aerostatic stability is compiled by using the APDL language provided by ANSYS.We calculated the critical wind speed of aerostatic instability of the bridge.The whole process of aerostatic instability of the bridge is analyzed and the instability mechanism of the bridge is discussed.It is concluded that the static wind load and structural deformation of the main girder of partially anchored cable-stayed bridge with rigid hinges increase nonlinearly with the the increase of wind speed.When approaching the critical wind speed,the stress of the cables near the wind side decreases significantly,and some cables relax and unload,resulting in the degradation of the overall stiffness of the structure.The interaction among structural deformation,aerostatic load and stiffness leads to structural instability and failure,and the main girder is in the coupled state of bending and torsion when instability occurs.(4)The effects of different initial wind attack angles,three-component force coefficients,loads on pylons and cables,nonlinearity,as well as rigid hinges on the aerostatic stability of cable-stayed bridges are investigated.The results show that the angle of attack and the three-component force coefficients have great influence on the static wind stability,while the wind loads on bridge pylons and cables have little influence on the static wind stability.Rigid hinges and ground anchor cables will not have a great impact on the aerostatic stability of the structure.Nonlinear factors have a great influence on the aerostatic stability,so it is necessary to consider the non-linear factors for the design and research of cable-stayed bridges.The conclusions drawn in this paper are reasonable and practical,and can provide technical reference for the future study of the aerostatic stability of such cable-stayed bridges,so as to facilitate designers to determine reasonable structural forms and take appropriate wind-resistant measures.