Study On Effects Of Erection Methods For Flutter Stability Of Long-span Suspension Bridges During Erection Stage

Today, with the span of suspension bridges becoming longer and longer, the stiffness and the damping of structures decrease obviously, so the flutter stability has become a very important factor in the design and construction of long-span suspension bridges. In the construction stage, particularly in the early stage, because the structure hasn't formed the final structural system, the stiffness particularly torsional stiffness of structures is less than the completion stage greatly, which makes the flutter critical wind speed dropping rapidly. However, the strong wind is usually unavoidable in the construction period. So how to improve the flutter stability during construction period has become an urgent need to study and solve.By taking the 4th nanjing suspension bridge over Yangtze river with the main span of 1418m as an example. First of all, based on the 3 dimensional multi-mode flutter analysis method, the flutter analysis program is compiled in MATLAB. And two classical examples are taken to prove the program's correctness and validity. Then the flutter stability of the completion and construction stage is analyzed. By contrasting with the result of wind tunnel experiments summarize the variation regularity of the flutter critical wind speed during the construction period. The influence of the flutter stability during the construction period is discussed when the deck stiffness and the structure damping are different. Finally, the flutter stability analysis of 4th nanjing suspension bridge over Yangtze river during the construction period with different deck erection sequence, non-symmetrical installation and gap installation is performed. The variation of the flutter critical wind speed during the suspension bridges construction period with various deck installation methods is studied. And some effective measures to improve the flutter stability during erection are taken. It is found out that the erection method from pylons to mid-span, non-symmetrical installation sequence and gap installation sequence can effectively improve the flutter stability in the construction stage of long-span suspension bridges particularly in the early erection stage.