Study On Structural Behavior And Aerodynamic Instability Of A Cable-Stayed-Suspension Hybrid Bridge

The research of cable-stayed-suspension hybrid bridges has always been a hot topic in the field of bridge science,but most of the research focuses on the mechanical properties and other aspects,while the research on cable-stayed-suspension hybrid bridges with separated twin-girder decks is less.In this paper,the integral steel box girder and separated twin-girder decks are used to draw up two super long span cable-stayed-suspension hybrid bridge schemes with a main span of 2100 m,and the static and dynamic characteristics and wind resistance stability of the two schemes are compared.The main work is as follows:(1)According to the previous research results,relevant bridge experience,and theoretical derivation formula,the main design parameters of the scheme of 2100 m highway cablestayed-suspension hybrid bridges are proposed.Two schemes of integral beam and separated beam are selected,and the approximate calculation formula is used to estimate the axial force at the key position of the main beam and the internal force of the tail cable of side span of cable-stayed section.Furthermore,the stability of the main beam is analyzed briefly.And it is found that The axial force of the main beam is normal and the stability is good,but the stress may be too large and the tension of the stay cable is too large.According to the results,we can adjust the design parameters appropriately,and finally improve the bridge scheme.(2)According to the analysis method and steps of the reasonable completion state of the cable-stayed-suspension hybrid bridges,the reasonable completion state of the two schemes is analyzed,and on this basis,the eight lane load is analyzed.It is found that the results of the two schemes,such as the axial force,bending moment,deflection and internal force envelope of the main beam,are similar to each other,but there are some differences in some areas,especially near the end sling and the tail cable of the side span.In addition,the basic frequency of the free vibration characteristic of the two schemes is similar.(3)The nonlinear aerostatic analysis program for the cable-stayed-suspension hybrid bridges is developed,and the nonlinear aerostatic effect of the two schemes is analyzed.The critical wind speed of aerostatic instability,the whole process deformation of the main beam and the stress change of the cable are obtained.It is found that the critical wind speed of the separated beam scheme is generally higher than that of the whole beam scheme.Considering the initial wind angle of attack,the difference of internal force development curves between the windward and leeward sides of the cable can explain the difference of torsional deformation and aerostatic instability of the main beam when the structure has different positive and negative angles of attack.The wind load will change of the free vibration characteristics of the structure,and the change is large when the wind speed is high;(4)According to the three-dimensional multi-modal flutter analysis method,the threedimensional flutter performance of the two schemes is analyzed,and the influence of additional angle of attack caused by the aerostatic effect on the flutter performance is considered.On the whole,the critical flutter wind speed of the separated beam scheme is larger than that of the integral beam scheme,but the main control modes of flutter of the two schemes are different.Considering the aerostatic effect,the critical wind speed will decrease in different degrees,while the main control modes of the flutter critical state have not changed much.