Flutter Analysis of Long-Span Bridges with Mode Coupling

• Main Authors: Fenq-Jiuan Lee, 李鳳娟
• Other Authors: Yuh-Yi Lin
• Format: Others
• Language: zh-TW
• Published: 1995
• Online Access: http://ndltd.ncl.edu.tw/handle/55212965963566144685

碩士 === 淡江大學 === 土木工程研究所 === 83 === In general, the sensitivity of the bridge structure to wind excitation greatly increases with the bridge span. Among the aerodynamic problems induced by turbulent wind, flutter and buffeting have been known as the most prominent ones. Aerodynamic forces can induce additional damping and stiffness which may cause the vibration modes of the bridge structure coupled together. The coupled modes will be achieve to a single mode, called flutter mode, at certain wind speed. In this paper, a numerical method is presented to predict the flutter velocity and to study the coupling effects on the buffeting response of long-span bridges. The self-excited forces are incorporated into the modal equations of motion for the calculation of the coupling properties of the normal modes. A complex-eigenvalue analysis combined with the iterative approach is applied to automatically evaluate the flutter velocity. Buffeting response can also be calculated by solving the coupled equations of motion. The results according to uncoupled motions are also provided for the purpose of comparsion with those according to coupled motions. A simple beam model and a cable-satyed bridge model are provided to verfy the flutter velocity and applicability of this method. The major difference of the buffeting response between coupled and uncoupled motions results from structural and aerodynamic coupling. The contribution of aerodynamic coupling become more significant as the wind speed increases.The results of both bridge models indicate that the structure displacements based upon mode coupling assumption tend to be larger than the uncoupling ones.