Hyperbolic Structures by Beckh Matthias

Author:Beckh, Matthias
Language: eng
Format: epub
ISBN: 9781118932704
Publisher: Wiley
Published: 2015-01-05T00:00:00+00:00

On the other hand, the achieved safety factors of the towers in Mykolaiv and Tyumen for the load case combinations at 1.39 and 1.20 are rather low. The two structures with their large tank volumes are a clear advance on the earlier installed water capacities – in the case of Mykolaiv, this was a five-fold increase in the top load of earlier structures. Obviously the confidence in the design and construction after more than ten years’ experience allowed the limits to be pushed further and the safety reserves of the system to be continuously reduced. To this can be added the improvement in the available steel quality and permissible steel stresses, which are discussed in the chapter “NiGRES tower on the Oka” (p. 96ff.). For example, the permissible steel stresses used in the historical calculations for the water tower in Tyumen are around 25 % higher than those used for the Mykolaiv tower.

The water tower in Dnipropetrovsk does not achieve a safety factor greater than 1 for purely vertical loading. This tallies with the story of its collapse, which can be attributed to stability failures and was discussed in contemporary specialist literature (see “The collapse of the water tower in Dnipropetrovsk”, p. 84f.). Using flexurally stiff connections to the intermediate ring, the load capacity would be increased by around 30 % – even though by doing this an acceptable level of safety would still not be achieved. This could have been done without great cost by the use of stronger intermediate rings, as the calculations in the section “Influence of the stiffness of the intermediate rings” (p. 54ff.) show. However, the choice of intermediate rings was not based on calculations. In the main, the depth of cross section of the intermediate rings was between 50 and 75 % of the depth of the vertical member cross section. In the case of large diameter intermediate rings – as is the case here – this relationship, which is determined independently of the radii, leads to cross sections with too little flexural stiffness.

Even if simplifications have been made for the analysed examples, and the selection may not be representative, the results show that the structures built later (for the loads considered) have a very low level of safety. This is all the more valid when it is considered that today’s steel grade S 235 was used for the calculations – which is probably rather optimistic for the earlier examples from the period studied.

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