Time domain vs. frequency domain characterization of aeroelastic forces for bridge deck sections

The characterization of unsteady transverse wind forces of bridge sections under oscillatory motion is commonly addressed in the frequency domain by means of the so-called flutter derivatives. Thin airfoil theory suggests that for streamlined bodies a time domain treatment is equivalent; in this case small-amplitude motions are assumed and superposition of effects can still be accepted. This observation led researchers to postulate the extension of this methodology to bridge sections, based on the analytical transformation of aeroelastic derivatives into time-dependent functions, to be used in step-by-step finite-element or equivalent simulations. In this paper the procedure for obtaining these functions from data in the frequency domain is reviewed, fully extended to the complete set of derivatives and applied both to streamlined and bluff deck sections. The validity of this approach has been only partially investigated in the past; assessment for bridge deck sections and its convenience with respect to frequency domain analyses are discussed, and applied to relative to a range of typical examples.