Analysis of long span bridge response to winds: Building nexus between flutter and buffeting

In current bridge aeroelastic analysis frameworks, predictions of flutter instability and buffeting response to wind fluctuations are treated as two separate procedures. The flutter instability is analyzed through the solution of a complex eigenvalue problem, offering information on how the self-excited forces influence bridge dynamics, especially the modal damping, and eventually drive the bridge to develop unstable flutter motion. On the other hand, the buffeting response is quantified through spectral analysis that involves the evaluation of a complex frequency response matrix/transfer matrix at discrete frequencies, offering prediction of the statistics of bridge response. The modal properties at varying wind velocities predicted through flutter analysis have not yet been explicitly employed in predicting and interpreting buffeting response. Furthermore, current buffeting analysis frameworks often regard the complex aerodynamic admittance functions as real-valued, neglecting the phase differences of buffeting force components with respect to wind fluctuations. In this paper, a unified analysis framework of integrating both flutter and buffeting analysis is presented. The buffeting response is explicitly expressed in terms of the bridge modal properties that are influenced by the self-excited forces and predicted through the flutter analysis. Closed-form formulations are provided for quantifying the variance/covariance of buffeting response. This framework not only is computationally more effective, but also sheds more physical insight into bridge aeroelastic response by explicitly linking the effects of self-excited and buffeting forces on bridge response. The effectiveness and accuracy of the proposed framework are illustrated through a long span suspension bridge example. The multimode coupled bridge aeroelastic response is discussed with an emphasis placed on the significance of complex aerodynamic admittance functions on buffeting response.