A case-study of double multi-modal bridge flutter: Experimental result and numerical analysis

• A wind tunnel test case of a complex double flutter instability in a long span bridge is presented.
• A multi-modal framework and a complete set of aerodynamic coefficients are necessary to simulate the phenomenon.
• The combination of several structural modes and sets of aerodynamic coefficients is studied.

An experimental double multi-modal flutter instability was recorded during wind tunnel tests on a full bridge aero elastic model. The analysis of this instability is presented in this paper, and it is studied with a multi-modal eigenvalue approach.It is shown that two different coupling mechanisms, one involving the symmetric modes and the other involving the anti-symmetric modes, lead to two different instabilities that occur at the same wind speed.The numerical analysis shows that a multi-modal framework and a complete set of aerodynamic coefficients are necessary to correctly estimate the flutter onset. The effect on flutter of structural and aerodynamic characteristics is discussed thoroughly, with a focus on structural modes and on the dependence of the aerodynamic coefficients upon the reduced velocity and upon the angle of attack.