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Wind and Structures
  Volume 32, Number 4, April 2021, pages 293-308
DOI: https://doi.org/10.12989/was.2021.32.4.293
 


The nose-up effect in twin-box bridge deck flutter: Experimental observations and theoretical mode
Maja Ronne, Allan Larsen and Jens H. Walther

 
Abstract
    For the past three decades a significant amount of research has been conducted on bridge flutter. Wind tunnel tests for a 2000 m class twin-box suspension bridge have revealed that a twin-box deck carrying 4 m tall 50% open area ratio wind screens at the deck edges achieved higher critical wind speeds for onset of flutter than a similar deck without wind screens. A result at odds with the well-known behavior for the mono-box deck. The wind tunnel tests also revealed that the critical flutter wind speed increased if the bridge deck assumed a nose-up twist relative to horizontal when exposed to high wind speeds – a phenomenon termed the "nose-up" effect. Static wind tunnel tests of this twin-box cross section revealed a positive moment coefficient at 0° angle of attack as well as a positive moment slope, ensuring that the elastically supported deck would always meet the mean wind flow at ever increasing mean angles of attack for increasing wind speeds. The aerodynamic action of the wind screens on the twin-box bridge girder is believed to create the observed nose-up aerodynamic moment at 0° angle of attack. The present paper reviews the findings of the wind tunnel tests with a view to gain physical insight into the nose-up" effect and to establish a theoretical model based on numerical simulations allowing flutter predictions for the twin-box bridge girder.
 
Key Words
    twin-box girder; flutter prediction; aerodynamic derivatives; nose-up effect; suspension bridges; wind tunnel test; numerical simulations; long-span bridges; force and moment coefficient
 
Address
Maja Ronne:1)Department of Bridges International, COWI, Parallelvej 2, 2800 Kongens Lyngby, Denmark
2)Department of Mechanical Engineering, Technical University of Denmark (DTU),Niels Koppels Allé, Building 403, 2800 Kongens Lyngby, Denmark

Allan Larsen:Department of Bridges International, COWI, Parallelvej 2, 2800 Kongens Lyngby, Denmark

Jens H. Walther:Department of Mechanical Engineering, Technical University of Denmark (DTU),Niels Koppels Alle, Building 403, 2800 Kongens Lyngby, Denmark
 

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