The paper examines two-dimensional force functions useful in the wind-respo
nse analysis of bluff bodies, such as bridges, that are elongated in the ac
ross-wind direction. Airfoil-type theoretical 2-D indicial, admittance, and
oscillatory force functions and their interrelationships are first recalle
d for their analogical value. Following this, a spectral force expression i
s developed for the lift on a bluff section due to a cross-wind with a vert
ical turbulence component. The expression proposed involves an aerodynamic
admittance that is based upon measured flutter derivatives for the bluff se
ction plus information on the coherence of vertical turbulence in the atmos
pheric boundary layer. (C) 2000 Academic Press.