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also be made by ‘system identification’ techniques applied to free vibration responses. The
approach can be extended, for example to include alongwind (horizontal) motion, making a
potential set of eighteen derivatives.
It will be noted that if the response is restricted to torsion only (or that the practical
magnitude of vertical response is too small to have a significant effect through the coupling
derivatives and ), corresponds to an aerodynamic damping

(3.54)

For an aerofoil is unconditionally negative, giving positive damping, albeit fairly small.
For sections subject to torsional instability replicates Figure 3.10. For simple vertical
motion the corresponding aerodynamic damping is

(3.55)

For an aerofoil noting (F being the real part of Theodorsen’s function, Figure
3.8), the aerodynamic damping commonly substantially reduces the vertical response to gusts.
It has also been found that this estimate of vertical motion damping is useful for a relatively
wide range of non-aerofoil sections.

3.4 REFERENCES

3.4.1
Books and journals
Bearman, P.W. (1981) ‘Aerodynamic loads on buildings and structures’, Wind Engineering in the
Eighties, CIRIA, London (chapter 5).
Bietry, J., Chauvin, A., Redoulez, P. and Augustin, V. (1994) ‘Elorn River Bridge, wind effects
modelling and structural analysis; paper given at Conference Cable Stayed and Suspension Bridges,
Deauville 2, pp. 153–62, APFPC Bagneux, Paris.
Blevins, R.D. (1994) Flow-induced Vibrations.
BRV (1990) A Criterion for Assessing Wind-induced Crossflow Vortex Vibration in Wind Sensitive
Structures (supplement to the Department of Energy Offshore Installations: Guidance on Design
and Construction), Brown and Root, London.
Cook, N.J. (1985) The Designer’s Guide to Wind Loading of Building Structures (Part 1),
Butterworths, London.
Cullen-Wallace, A.A. (1985) ‘Wind influence on Kessock Bridge’, Engineering S’tructures 7:
(January).
Davenport, A.G. (1961) ‘The application of statistical concepts to the wind loading of structures’,
Proc. Instn. Civil Engineers 19 (August): 447–72.
——(1962) ‘The response of slender, line-like structures to a gusty wind’, Proc. Instn Civil Engineers
23 (November) 389–407.
——(1964) ‘A note on the distribution of the largest value of a random function’, Proc. Instn. Civil
Engineers 28 (June): 187–196.
Doucet, Y.J. and Nordhus, A. (1987) ‘Vibration monitoring of a flare boom’, Texas OTC5523,
Offshore Technology Conference, Houston.