Flutter analysis methods for bridges stabilized with eccentric wings

Uwe Starossek,Rudolf T Starossek

doi:10.1016/j.jweia.2021.104804

Abstract

Analysis methods for computing the flutter speed of bridges stabilized against flutter by stationary wings are presented. The wings are placed outboard the bridge deck to achieve a large lateral eccentricity, which enables them to produce enough aerodynamic damping to effectively raise the flutter speed. Given the focus on flutter, other wind effects are neglected. The analysis can thus be carried out in the frequency domain. The most sophisticated method is based on a specially developed finite aeroelastic beam element, used for modelling a bridge-deck-plus-wings segment, leading to a multi-degree-of-freedom analysis. Such analysis is recommended if the wings do not extend over the full length of the bridge, a design choice that benefits cost efficiency. Second, a simplified two-degree-of-freedom flutter analysis method is described. Simplification is achieved by establishing the wind forces on the wings assuming quasi-steady, instead of unsteady, flow and taking them into account as additional damping and stiffness. Results of example calculations are compared to those of the multi-degree-of-freedom flutter analysis. Finally, it is shown how torsional flutter of a bridge equipped with such wings can be treated in a single-degree-of-freedom analysis. The method is applied to the first Tacoma Narrows Bridge.

Highlights

Bridges are exposed to various wind effects, in particular the static wind force, buffeting, vortex shedding, and flutter
For modelling the torsional deformation of the bridge deck, a minimum number of two degrees of freedom is required, which correspond to the angular displacements of the element end nodes about the longi tudinal axis (a respective finite aeroelastic beam element without wings is described by Starossek (1992, 1993))
Results obtained with the FORTRAN program, implementing the finite aeroelastic beam element and MDOF flutter analysis method described above, are compared to those obtained from 2-DOF flutter analyses using the method described in Section 5.1 below

Summary

Introduction

Bridges are exposed to various wind effects, in particular the static wind force, buffeting, vortex shedding, and flutter. Instead of by closed-form complex functions, the unsteady aerodynamic forces are described by empirical real functions determined with sectional bridge deck models in the wind tunnel In this approach, the spatial system is generalized to two degrees of freedom, heave and rotation, using the first vertical bending and torsional modes of vibration. When this length is less than the length of the bridge, the aerodynamic properties are no longer constant along the bridge axis and, (mainly) the torsional compo nent of the flutter mode shape differs from the respective vacuum mode shape To accurately take this into account, a multi-degree-of-freedom (MDOF) analysis method is developed. While not within the scope of this paper, this means that the wings improve serviceability and reduce fatigue damage

General

Contributions of bridge deck

Modelling alternatives

Method

Example

Conclusions