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Oscillation of a structure induced by vortex excitation is likely to occur at frequencies quite different from the natural frequency of the structure because of the locking-in phenomenon. Effective damping by means of a passive mechanical system requires that the system be capable of operating over a large range of forcing frequencies under the exciting forces which may vary in direction and intensity. A damping device based on the principle of energy dissipation by impact has been developed for this purpose. It has a nonlinear response to displacements, and is suitable for operation at relatively low frequencies. Selected experimental results are
presented in this paper.
Professor A. L. L. Baker (F): At one time it appeared that we might use a limited tensile strain normal to uniaxial load of cube strength x Poisson's ratio / E
as the general criterion for ultimate strengths for all practical purposes. Indeed, if we assume that the ratio of stress over strain at the ultimate limit state is 2 x l0 to the power 6, and that the Poisson's ratio is 1 over 4.5, we can derive, for a multiaxial strained cube, an equation that fits the mean values shown in Fig A1 in the paper. It also fits the higher ranges, if E is reduced in all the terms of the basic strain equation to agree with low values indicated by the curves in Fig A4 and provided that secondary strains do not at some point reverse.
. . spare that tree
Mr. C. G. H. Jofeh is clearly a man concerned about nature conservancy. He writes: I read with interest the letter from Mr. A. Billingham (November 78). What interested me
was not the question of what the building regulations do or do not say, but the attitude of mind of the author that I inferred from what he said about the trees.