| For multi-tower cable-supported bridges, there are three main longitudinal structural systems: float, fully constraint and part constraint system. However, existing research regarding the impact of different longitudinal structural systems for the dynamic properties and seismic performance of multi-tower cable-supported bridge structure is still a lack of sufficient understanding. How in-depth study of multi-tower cable-supported bridge seismic performance and capacity damping control method, the establishment of appropriate analytical methods and key technology to improve its security operations and to resist earthquakes, is one of the important problems for bridge engineering to solve. In this dissertation, with Jiashao bridge and the Qiongzhou Strait cable-stayed bridge as engineering background, the impact of different tower and beam longitudinal restraints in the form of multi-tower cable-supported bridge seismic performance is analyzed. For different longitudinal structural systems, multiple sets of passive damping control method are given and parity analyzed. Finally by the response surface method and multi-objective optimization genetic algorithm gives damping schemes. The main contents and achievements in this paper are as follows.1. The finite element models of Jiashao Bridge and the Qiongzhou Strait cable-stayed bridge are established based on Ansys, and the static and dynamic characteristics of these two long-span bridges with different longitudinal structural systems are analyzed. The results show that:different tower and beam longitudinal restraints mainly change the girder bending and lateral bending stiffness of multi-tower cable-supported. With the transition from fully constraint of the system to full floating system, the bending stiffness of girder is reduced while the corresponding vibration period is extended. What’s more, different tower and beam longitudinal restraints have more significant effects on girder vertical bending modes and lateral bending modes than torsional vibration modes or the scoliosis modes of main towers.2. Ansys is used for the history analysis under earthquake of multi-tower cable-supported bridges, the seismic responses of different longitudinal structures are compared. The results show that:The floating longitudinal structure has large tower displacement and relative displacement between tower and girder but small tower bottom longitudinal internal force responses. As for the fully constraint longitudinal structure, it is just opposite to the above situation:tower bottom longitudinal internal force responses are large while the displacement responses of tower and girder become small. Part constraint system has its unique mechanical properties with small displacement reaction and longitudinal internal force responses at the bottom of the tower if it is not constraint with girder, or the force response will get much larger.3. Schemes which adapt damping are proposed for different longitudinal systems, analysis and comparisons of the effects of different damping schemes show that:elastic cable or viscous fluid damper that set between tower and girder can significantly reduce longitudinal displacement responses of multi-tower cable-supported bridges, but tower bottom longitudinal internal force responses may be exaggerated. In order to obtain significant control effects, the parameters of damping systems should be reasonable. In the integrated use of the elastic cable and viscous fluid damper schemes, two devices can work together to achieve better control effects. Reasonable damping schemes are proposed for float and part constraint system.4. Response surface method and multi-objective genetic algorithm are used for optimized analysis of multi-tower cable-supported bridge float damping systems and part constraint mixed damping systems. Damping effect response using response surface fitting ideal and can be used for the seismic response of the optimal control design. Optimized results are obtained using multi-objective genetic algorithms optimization damping analysis. |
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