Effects of Flutter Derivatives on Critical Speed of Long-Span Bridges

• Main Authors: Jeng Horng Shieh, 謝政宏
• Other Authors: Yuh-Yi Lin
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/98239591879726545283

碩士 === 淡江大學 === 土木工程學系 === 87 === Abstract： The developments of bridge construction techniques have led to the wide use of long span in bridges. The effects of aerodynamic forces on such bridges increase significantly with the span length. While the negative aerodynamic damping is equal to the structural damping at some wind speed, the flutter phenomenon will occur, that is, the bridge will result in failure. The flutter can be attributed to the self-excited forces that are commonly expressed by flutter derivatives, which are measured from section model tests. For the case of one degree-of-freedom flutter, the effects of A2 is known as the most important. However, for the case of coupled flutter, the flutter derivatives are related to each other, the influence of each individual flutter derivative on critical wind speed is difficult to justify by the previous methods. In this study, an iterative approach is used to investigate the effect of each flutter derivative on critical wind speed. By using this method, the aerodynamic damping resulted from each flutter derivative can be calculated and the influence of each flutter derivative on coupled flutter can be better understood. The applicability and validity of this method are examined by a comparison between the complex eigenvalue method and this present method. Through a parametric study, the effects of flutter derivatives, the ratio of the first torsional frequency to the first vertical frequency, and bridge span length on flutter wind speed are investigated. The results show that the effects of A1 ,A2 ,A3 and H3 on critical wind speed of coupled flutter are more significant than the other flutter derivatives. The increase of the ratio of the first torsional frequency to the first vertical frequency and the decrease of bridge span length can increase the critical wind speed.