Practical Diagrammatical Technique for 3-DOF Bridge Flutter Analysis

Abstract

For long bridges with bluff deck sections, the influence of lateral wind loads on flutter performance needs to be carefully investigated. In this paper, an advanced three-degree-of-freedom (3-DOF) analytical framework considering lateral aeroelastic effects is developed to refine bridge flutter analysis. This approach uses high-order nonlinear equations to determine twin critical flutter parameters, i.e., velocity and frequency. An optimization model to determine the critical flutter parameters is developed. A practical diagrammatical technique is proposed to solve this problem, which is an improvement over the traditional optimization techniques. The intuitiveness and effectiveness of the diagrammatical technique is fully verified using a numerical example. The optimization model and diagrammatical technique are applied to the 3-DOF flutter analyses of two bridges with bluff deck sections. It is revealed that the flutter derivatives H5∗, H6∗, A5∗, A6∗, and Pi∗ (i=1,2,…,6) play an insignificant role in flutter performance of both bridges. If H5∗=H6∗=A5∗=A6∗=0, the Pi∗ (i=1,2,…,6) will be paralyzed, and the influence of only the conventional eight flutter derivatives, those related to the heaving and torsional motions, can be considered. On the other hand, if Pi∗=0 (i=1,2,…,4), H5,6∗, A5,6∗, and P5,6∗ will also lose efficacies. These novel findings are first presented, which can be steadily proved by the explicit expression of the optimization model. This study presents a valuable insight into the flutter characteristics of both bridges and explores the roles in the flutter onset played by various parameters. Further, even with bluff deck sections of both bridges, the analytical results of 2-DOF vertical-torsional coupled flutter for the Akashi Kaikyo Bridge and the 1-DOF torsional flutter for the Suramadu Bridge are coincident with the experimental observations. Thus, the effectiveness of analytical framework is again verified.