Damping Measures to Control Wind-Induced Vibrations
The possibilities of passive and active control of wind-induced vibrations of structures in civil engineering are presented. The concept of control by means of mechanical and aerodynamic devices is discussed using results of theoretical and experimentel i
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G.H. Hirsch Aachen University of Technology, Aachen, Germany
Abstract The possibilities of passive and active control of wind-induced vibrations of structures in civil engineering are presented. The concept of control by means of mechanical and aerodynamic devices is discussed using results of theoretical and experimentel investigations (model tests and fuH scale examinations). The effectiveness of structural control and the advantages and disadvantages from engineering point of view will be considered. Case studies will be presented .
H. Sockel (ed.), Wind-Excited Vibrations of Structures © Springer-Verlag Wien 1994
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G.H. Hirsch
1. INTRODUCTION
Damping measures for wind induced vibrations of structures means vibration control in a general understanding. It is to distinguish between passive (selfgoveming) and active (feedback) control. In engineering practice, controlling vibrations in structures is partly art and partly science because, though one can obtain data needed to develop and optimize the appropriate control measures from analysis or experiment, in practice one is constrained by factors of time, equipment, and economics and is often obliged to make decisions conceming the control measures without having complete information. This is to be taken into consideration especially in case of control wind induced vibrations of structures. This means that guesses must be made, past experience must be drawn on, and less than optimum: measures must be sought which do the job without necessarily being the most perfeet solution. One of the least understood aspects of the design of a damping treatment is determination of how much damping is really needed to deal with a given problem. This question cannot be resolved unless there exists an understanding of how much damping is in the original structure. The definition of this initial damping is very important, because all improvements are related to that value. To illustrate this matter, consider the difference in structural response between so-called "built-up" structures or welded (also integrally) structures. Built-up structures are joined together or assembled by mechanical fasteners, such as rivets, bolts, and screws. Increasing the built-up structure damping by a factor of, say, 10, is considerably more difficult than for welded structures. Different damping treatments and approaches have to be taken for different applications, depending on the initial structural damping values. The usual approach in the application of damping treatments to structures is to optimize the system for maximum damping only. Such an approach, although correet from the point of view of damping optimization, neglects the fact that other modal parameters can change whenever a damping treatment is applied or incorporated into a structure. Therefore it is frequently essential to consider the variation of all three parameters damping, mass and stiffness - and try to optimize the damping treatment for all three parameters and not merely for one. Relating to the control of dynamic respon
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