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Wind and Structures
  Volume 25, Number 3, September 2017, pages 283-299
DOI: https://doi.org/10.12989/was.2017.25.3.283
 


Aerodynamic admittances of bridge deck sections: Issues and wind field dependence
Zhitian Zhang, Weifeng Zhang and Yaojun Ge

 
Abstract
    Two types of aerodynamic admittance function (AAF) that have been adopted in bridge aerodynamics are addressed. The first type is based on a group of supposed relations between flutter derivatives and AAFs. In so doing, the aero-elastic properties of a section could be used to determine AAFs. It is found that the supposed relations hold only for cases when the gust frequencies are within a very low range. Predominant frequencies of long-span bridges are, however, far away from this range. In this sense, the AAFs determined this way are of little practical significance. Another type of AAFs is based on the relation between the Theodorsen circulation function and the Sears function, which holds for thin airfoil theories. It is found, however, that an obvious illogicality exists in this methodology either. In this article, a viewpoint is put forward that AAFs of bluff bridge deck sections are inherently dependent on oncoming turbulent properties. This kind of dependence is investigated with a thin plate and a double-girder bluff section via computational fluid dynamics method. Two types of wind fluctuations are used for identification of AAFs. One is turbulent wind flow while the other is harmonic. The numerical results indicate that AAFs of the thin plate agree well with the Sears AAF, and show no obvious dependence on the oncoming wind fields. In contrast, for the case of bluff double-girder section, AAFs identified from the turbulent and harmonic flows of different amplitudes differ among each other, exhibiting obvious dependence on the oncoming wind field properties.
 
Key Words
    bridge; bluff; aerodynamic admittance; wind field; flutter derivative
 
Address
Zhitian Zhang and Weifeng Zhang:Wind Engineering Research Center, School of Civil Engineering, Hunan University, Changsha 410082, China;
Hunan Provincial Key Laboratory of Wind and Bridge Engineering, China
Yaojun Ge: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, ShangHai, China
 

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