Application of System Identification on Full Bridge Model Test in Wind Tunnel

• Main Authors: Yen-Ming Jen, 任彥銘
• Other Authors: Yuh-Yi Lin
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/98614518030160779110

碩士 === 淡江大學 === 土木工程學系碩士班 === 99 === Regarding the wind effects on bridges, wind tunnel tests have been most important tools. Specifically, wind tunnel tests include section model and full bridge model tests, in which the characteristics of the wind field are simulated as well. Then, the response of the bridge scale is measured and the coefficients and flutter derivatives of the wind are obtained. Nevertheless, we do not know exactly whether the flutter derivatives derived from section modal tests correspond to the real aerodynamic behavior of the whole bridge. Correspondingly, this study adopts the full-bridge model wind tunnel tests and the results of field measurements in order to analyze the flutter derivatives. In turn, the results are compared with those obtained form the section model tests and the differences between the two sets of results are discussed. As far as the system identification is concerned, this study applies the modal splitting concept to the random decrement method (RD method) in order to identify the natural frequencies and damping ratios of different modes at various wind speeds. Then, these data are substituted into the equation of bridge motion to obtain uncouple flutter derivatives (H1*、A2*、A3*、P1*). Eventually, the flutter derivatives derived from both the full-bridge model tests and the field measurements are compared with the results from the bridge section model test. Based on the research findings, the aerodynamic effects of both the flutter derivatives obtained from a section model tests experiment (H1*、A2*、A3*) and the flutter derivatives calculated from an approximate formula (P1*) are shown relatively larger than those derived from the full-bridge model tests and field measurements.