Advanced analysis of coupled buffeting response of bridges: a complex modal decomposition approach

This paper presents a framework based on a complex modal decomposition technique for predicting coupled buffeting response of bridges in both time and frequency domains. The coupled equations of motion in structural modal coordinates with frequency dependent aeroelastic self-excited terms are approximated by frequency independent state-space equations, without augmented aerodynamic states, which retain the complex modal properties of the original system. These equations are then decomposed into a set of uncoupled equations of motion for buffeting response analysis. The frequency dependent unsteady buffeting characteristics and their spanwise correlation are considered in both frequency and time domain analyses instead of invoking the customary quasi-steady assumption. This framework significantly enhances computational efficiency in the frequency domain analysis by avoiding system matrix inversion at each discretized frequency when evaluating the transfer function matrix. Furthermore, it also offers simulation of buffeting response in the time domain that includes frequency dependence of buffeting and self-excited forces. A detailed discussion concerning the complex modal frequencies, damping ratios, mode shapes, and the significance of structural modes on the multimode coupled buffeting response is provided. This helps to glean additional insight and to improve our understanding of the underlying physics of wind-structure interactions. Examples of long span suspension bridges are provided to illustrate the proposed scheme and to demonstrate its effectiveness. (C) 2002 Elsevier Science Ltd. All rights reserved.