Prediction of cable-supported bridge response to wind: coupled flutter assessment during retrofit

Abstract

As is well known, long, suspended bridge spans require, in the design stage, careful study of their resistance and response to site winds. This has driven, on the one hand, detailed quantitative observation of bridge models in the wind tunnel and, on the other, a steady development and refinement of parallel theory. Currently, both aspects have arrived at good stages of sophistication, though with continued room for improvement. Successes in the extension of bridge spans to record-breaking lengths are due in particular to progress in wind-resistant design: a primary component in the design of long-span bridges. Recently, multi-mode flutter and buffeting analysis procedures have been developed. These procedures, which were based on frequency-domain methods, take into account the fully coupled aeroelastic and aerodynamic response of long-span bridges to wind excitation. This paper shows an example of application of the theory to the stability (flutter) analysis associated with the retrofit of an existing long-span bridge in North America. This example not only demonstrates the application of the theory to a real structure, but also serves to highlight the important insights into the structural behavior that are revealed by this approach. Interestingly, the results show that even for a relatively short-span bridge, aeroelastic coupling between modes of vibration can occur due to the peculiar structural dynamic characteristics of the bridge especially during modifications, and this coupling must be considered. The paper seeks to make the interested structural/bridge engineer aware of recent developments in the field, outlines the complementary alternative procedures available for assessment of wind effects on cable-supported bridges, and provides an overview of the basic steps in the process of a typical aerodynamic analysis and design.