On flutter and buffeting mechanisms in long-span bridges

Abstract

Using linear formulations throughout, the present paper reexamines the problem of the three-dimensional dynamic response of long, flexible bridge decks to wind, particularly with the modern cable-stayed bridge in view. There are some particular motivations for the approach presently used. First, it has been observed that the bridge deck, the principal attractor of aerodynamic forces, undergoes three-dimensional motion having not only vertical and twist components, but lateral sway as well. This is a pronounced feature of many cable-stayed bridge vibration modes; and, since lateral sway can play a strong, contributory role in total aeroelastic action, it is important that its effects be included. Second, under buffeting by turbulent wind, total bridge response is random in the time domain, precluding the direct expression of aeroelastic forces via the well-known flutter derivatives which are applicable only to harmonic motion. In principle their role must be supplanted for general motions by the integrated effects of those motions as weighted by the corresponding aerodynamic indicial functions. However, to date such indicial functions have themselves been derived only through inverse Fourier transformation of experimentally obtained flutter derivatives; hence there exists an impetus to carry out the entire analysis in the frequency domain, where the original flutter derivatives can be used directly. The details of this procedure and its consequences regarding both the stability and level of bridge deck response are pursued in the body of the paper.