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The phenomenon of wind-induced transverse vibrations occurs in steel chimneys. The excitation is caused by regular alternating air forces, which develop during the separation of so-called Karmann vortices. The …
The phenomenon of wind-induced transverse vibrations occurs in steel chimneys. The excitation is caused by regular alternating air forces, which develop during the separation of so-called Karmann vortices. The transverse vibrations often determine the design, i.e. the chimney costs are influenced by this phenomenon, among other things. In Germany, steel chimneys are designed in accordance with DIN 4133. It is expected that the European standard currently being drafted will largely follow the German standard, despite the sometimes conflicting opinions of representatives from other countries. The prerequisite for this is the provision of convincing arguments on the basis of measurement material obtained from installed chimneys over sufficiently long periods of time.
In the context of the present work, long-term observations on four original chimneys provided the material for determining the transverse vibration stress from the amplitude and number of cycles (load spectra). This made it possible to check the service life calculation according to current theories of damage accumulation, as they form the basis of ERUROCODE 3, Section 9, Material Fatigue (published in Germany as DIN V ENV 1993). DIN 4133 obtains its service life statement under the assumption of constant alternating loads and the same vibration amplitude (single-stage collective). However, the real load spectra obtained during the measurements are multi-stage. For example, the naturally high loads - low number of cycles and high vibration amplitude - which only rarely occur during special wind events, are greater, sometimes even considerably greater than the single-stage loads used for the calculation in accordance with DIN. Graded load classes were formed according to the actual vibration stress and a service life prediction was obtained from these using a characteristic curve for fatigue strength ( Wöhler curve) that takes into account the accumulation of damage. Using the safety factor for fatigue strength on which DIN 4133 is also based, a service life of over 50 years is obtained for all the chimneys analysed. This proves that the chimneys designed in accordance with DIN 4133 are stable. Supplementary variation calculations with different approaches regarding the structural damping and the partial safety factor show the fundamental relationship between service life and structural damping. They show in which cases DIN 4133 definitely sets too stringent requirements and they indicate borderline cases in which there is a tendency to particularly high transverse vibration. The investigations form a reliable argumentation aid for the adoption of DIN 4133 for the design of steel chimneys in European standardisation. Furthermore, they show possibilities for refining the calculation for a safe and economical design of steel chimneys. STUDIENGESELLSCHAFT STAHLANWENDUNG e.V.
Machine-translated title and description. The document itself is in German.
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