Fatigue strength of attractions: how have the normative reference changed over the last 20 years?
 
THE EVOLUTION OF FATIGUE STRENGTH DETERMINATION ON ATTRACTIONS
by Enrico Fabbri
 
Changes to the standards that apply to determining fatigue strength have considerably increased the minimum endurance limit of attractions.

The 1990s saw German manufacturers experience major difficulties, no longer being able to supply their customers attractions at affordable prices. In those years, many Italian manufacturers started to design attractions in compliance with DIN-4112, and market them with TÜV certification. In this period, many manufacturers started applying DIN-15018 for fatigue testing their structures. This standard had been devised for the construction of cranes, and was related to DIN-4112. This standard established, among other things, that structures had to be designed so as to withstand at least 2 million operating cycles. The theory underlying the ‘German philosophy’ was based on the concept that after 2 million cycles without breakages, the structure could work ‘indefinitely’.

Standard DIN-15018 was incorporated into EN-13814 in 2007, and was used by all manufacturers for several years. A few years ago, this standard was amended, increasing the minimum fatigue limit to 5 million cycles (from the previous 2 million). The significant increase in this requirement led to the structures becoming heavier, and often required important components of many attractions to be redesigned.

DIN-15018 has now been abolished, following the entering into force of the new standard for metal constructions called the Eurocodes. This once again shuffled the deck, so to speak, introducing the concept that an attraction must be designed to withstand fatigue for at least 35,000 operating hours. Consequently, the reference parameter is no longer “operating cycles”, but rather “operating hours.”

This difference in concept is crucial, and the application of the Eurocodes requires designers to establish a series of attraction operating cycles, for example at full load or with half the number of passengers, and check the cumulated fatigue/stress on the structures over time; obviously, the sum of fatigue-stress over 35,000 hours must not cause the structure to break. It seems very simple in theory, however introduction of the Eurocodes has made work more complicated for the designers and engineers who need to carry out the calculations on the structures, compared to the previous DIN-15018, which was much more schematic and simpler to apply.

An exhaustive explanation of the evolution in these standards would occupy a huge amount of space, and these topics mainly concern the engineers who need to apply them. The main point that I want to make, however, is that the standards for determining the fatigue strength of structures on attractions have changed considerably over the last 20 years; with each change, the attractions have been strengthened in their design and consequently in their ability to withstand fatigue.

Another concept worth underlining is that an attraction is more subject to fatigue only based on the number of operating cycles/hours, and not its age.

 

 

 

Written by Mr. Enrico Fabbri enrico@fabbrirides.com
Article originally published in Games Industry (Italy) magazine
Original date: May 2015

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