MEASUREMENTS OF FLUTTER DERIVATIVES OF A BRIDGE DECK SECTIONAL MODEL

Aeroelastic phenomena should be considered during the design phase of long span bridges. One of the aeroelastic problems is flutter, the dynamic instability that may cause structural failure at a wind speed called the flutter speed. The prediction of flutter speed of a bridge needs a thorough modelling of bridge stiffness, inertias, and especially its unsteady aerodynamic forces. The potential flow theory is not applicable to calculate unsteady aerodynamics of oscillating bridges due to their non-streamlined complex geometry, and the non-avoidable flow separation. For these reasons, a semi empirical model proposed by Scanlan is used to describe unsteady aerodynamic forces on an oscillating bridge deck. In this model, relation between unsteady aerodynamic forces and motion of the bridge is modelled using parameters known as flutter derivatives. The values of flutter derivatives can be identified from the free vibration responses of an elastic bridge at several wind-speeds. This paper presents wind tunnel tests and flutter derivatives identification of a sectional aeroelastic bridge model. Modified Ibrahim Time Domain method was applied to identify the eigenvalues and eigenvectors of the model at each wind speed, from which the flutter derivatives can be calculated. The results show that the measurement procedure is able produce flutter derivatives, which are in good agreement with those obtained by other researchers.