The Study Of Dynamic Characteristics Of Triple-tower Double-span Suspension Bridge During Construction

A new wave of researching multi-tower-multi-span suspension bridge is set off at home and abroad by the completion of the first kilometric triple-tower-double-span suspension bridge, the Taizhou Yangtze River Highway Bridge, which open to traffic at the end of 2012. Soon afterwards, the Maanshan Yangtze River Highway Bridge and the Yingwuzhou Yangtze River Highway Bridge are also completed in 2013 and 2014 respectively. However, because of the unmatured research of this suspension bridge, it is no realized that the bridge under construction may be more dangerous than the finished bridge when suffer a strong wind action.In order to realize the dynamic stability of triple-tower-double-span suspension bridge during construction and further propose some countermeasures, the vibration performances of this kind of bridge are studied and some unique characters are analyzed. Some finite element models are established respectively for the tower-cable system and the tower-cable-girder system. The accuracy of models is tested by the Irvine free vibration linear theory. The modal characters of triple-tower-twin-span tower-cable system and tower-cable-girder system are analyzed base on the definitions of local and global vibration mode.The results indicate that the triple-tower-twin-span tower-cable system not only still holds the modal characteristics of the components of tower-cable coupling system but also has unique modal characteristics. The swinging motion of coupling system, at lower natural frequencies, has uncoupled from the in-plane motion. The system generates some new natural frequency and vibration modes. That the lower order modes of side span cables couple the higher order modes of main span cables, in some specific mode property and modal combination, will be generate the corresponding local in-plane and out-of-plane vibration and global in-plane and out-of-plane vibration in tower-cable system. The most vibrations are cable-dominated modes and the rest are tower or girder dominated because of the obvious influence between girders and cables. The out plane and in plane vibrations of cables respectively excite the swing, lifting and torsional mode of girders. Due to the modal properties, in phase or out of phase, of two cables in the same span and the modal combinations between two main span cables, the modal groups are divided clearly by the frequencies and vibration modes. Along with the increasing number of girder unit erected, the girder is built up and the frequencies of girder-dominated mode are rising. The different degrees of changes of each modal frequency generate modal transcend phenomena reflects that the instability of dynamic characteristics during the forming process of girder. To improve the wind resistant stability of multi-tower suspension bridge during construction, the thesis presents the way of setting wind resistant cable and the countermeasure improves the flutter critical wind speed of stiffening girder effectively.