Research On Flutter Modes Of Suspension Bridges With Three Towers And Its Whole Process Simulation

Compared with common double-tower suspension bridges, the main spans of multi-tower suspension bridges can be greatly shortened, and the cables' tension stress, the size of anchorage, also the cost are thus reduced significantly. Multi-tower suspension bridges have great crossover capability and have a broad application prospects in sea-crossing and island -linking projects in the future.However,multi-tower suspension bridges have lower structural stiffness and therefore become more susceptible to wind effects. Therefore, research on wind instability of them has theoretical and engineering importance. Flutter mode transition was discovered in wind tunnel test of full model of Maanshan Bridge. To study the mechanism of this particular phenomenon, main research works are conducted as follows:(1) Development history of multi-tower suspension bridges was introduced firstly. Then,it carried on the retrospect of flutter theories and some accidents caused by wind Finally, the phenomenon of flutter mode transition of Maanshan Bridge was described in detail.(2) Flutter derivatives of Runyang Bridge's deck was identified using Fluent software. To test the reliability of numerical method, comparisons were made between the identified and experiment values. After that, preparing for the analysis of frequency domain and time domain of flutter, flutter derivatives of middle-tower section of Maanshan Bridge was obtained using numerical wind tunnel.(3) To evaluate the effect of towers vibration on the flutter of the Maanshan birdge, full-mode flutter analysis is conducted for four different situations like only considering self-excited forces of decks, only considering self-excited forces of the middle tower, only considering self-excited forces of side towers and considering self-excited forces of both the middle tower and side towers. Then,time-domain analysis is conducted to test the correctness of frequency domain analysis.(4) Time evolutionary power spectral and the instantaneous phase difference of wind tunnel test signal of Maanshan Bridge's full model were obtained by means of the theory of wavelet transform. Through that, it can reflect the phenomenon of flutter mode transition. Then, the phenomenon was discussed in the degree of nonlinear oscillation and internal resonance.(5) To examine the validity of step-by-step analysis, flutter mechanism of idealized th in plate is analyzed using this method. Comparison is then made with the result of comp- lex eigenvalue analysis. After that, flutter mechanism of a rectangular plate is analyzed to explain 'branch switch'. Finally, the flutter mechanism of Maanshan Bridge's deck was an-alyzed, also, 'branch switch' occurs. So, It can be concluded that there's some relationship between flutter mode transition and 'branch switch'.