Evaluation of 2D coupled galloping oscillations of slender structures

The necessary conditions for the occurrence of 2D coupled galloping oscillations and a description of the set of general differential equations for 2D coupled galloping vibrations are established in this paper. A procedure to predict the 2D coupled galloping oscillations is proposed. Wind loading was treated as a stochastic process including mean and fluctuating components caused by atmospheric turbulence. The formulae and the procedure presented permit a better assessment of galloping oscillations of a prismatic structure which has the same natural frequencies-in the directions of the two orthogonal horizontal axes. The effects of turbulence on 2D coupled galloping are investigated. It is shown that 2D coupled galloping oscillations mainly occur in the cross-wind direction. The effect of the turbulence integral scale an the onset wind velocity of 2D coupled galloping oscillations is negligible. However, the turbulence integral scale has certain influences on the rms response both in the along-wind and the cross-wind directions when the wind velocity is equal or close to the onset wind velocity for galloping. An increase in the turbulence integral scale in the range of 10-40 m considered in this paper increases the galloping response. (C) 1998 Elsevier Science Ltd. All rights reserved.