Analysis On Design Parameters And Static-dynamic Properties Of Long-span Steel-pylon Cable-stayed Bridge

The long-span steel-pylon cable-stayed bridge has superior seismic performance and it can take advantage of overcapacity of domestic steel effectively but there are only three completed steel-pylon cable-stayed bridges with main spans over 400m and the main towers of them are all steel-concrete composite structures.A theoretical model of cable-stayed bridge with full-steel towers is established by consulting the bridge span distribution and section size of the Nanjing 3rd Yangtse River in the paper.By analyzing the static and dynamic characteristics of the theoretical model which differs from its original design,the main research work has been completed as follows.(1)On the basic of the thorough research on documentation,domestic and foreign development situation of the steel-pylon cable-stayed bridges is investigated,structural forms and mechanical properties of the main tower are summarized,static and dynamic calculation theories which can provide the theoretical basis for the parametric analysis of the steel tower are introduced.(2)The finite element model is built by the specialized bridge software.The cable force of the completed bridge stage is adjusted.The verticle deflection of the main beam,the stress amplitude and safety factor of stay cables,the stress of the main beam and the main tower,the first kind stability of bridges at three typical construction stages(the bare tower stage,the maximum double cantilever stage,the maximum single cantilever stage)are examined.The free vibration characteristics of the theoretical model are calculated and discussed(3)When the number,position and rigidness of the tower crossbeams are changed,the effect of them on the lateral displacement and the stress distribution of the main tower as well as the first kind stability coefficient of bridges at three typical construction stages is analyzed.The effective measures for improving stiffness and strength of bridges at the completed bridge stage and stability of bridges at the construction stages by adjusting the layout of the tower crossbeams are induced.(4)For modeling methods of pile foundation beneath towers and piers in the finite element software,the mass of the tower and the longitudinal stiffness of tower-beam estraint,the analysis results of their effect on structural seismic response explain the necessity of establishing pile foundation and considering soil-pile interaction for calculating seismic response precisely.In the paper,the influence of the main tower's mass change caused by adopting lightweight materials on structural seismic response is researched.Relatively favorable longitudinal stiffness of tower-beam estraint for earthquake resistance is obtained.In summary,the conclusions of static-dynamic analysis on six tower-related parameters can provide certain technical reference for the parameters setting of similar steel-pylon cable-stayed bridges.