Technical choices in the design of concrete foundations can have a big impact on the fatigue resistance of an attraction’s anchoring.
 
THE IMPORTANCE OF CONCRETE FOUNDATION DESIGN
by Enrico Fabbri
 
The design of the system that anchors an attraction to its concrete foundations is probably one of the most delicate aspects of any attraction. Many professionals don’t have a clear understanding of which solutions are most appropriate and the builder’s experience is often insufficient. To dispel any doubts, I would like to underline that the system for calculating and designing concrete foundations for small/middle-sized attractions and for basically static constructions is not very difficult, and therefore only rarely does a potential risk appear.

Things are very different, on the other hand, when the attraction to be anchored to the ground is big and relieves great transverse stresses onto its base. In this case, the project of the attraction’s steel base and the project of its concrete foundations should both be entrusted to a very skilled and meticulous professional. In sum, the attraction’s movement relieves big forces onto its base – and therefore also onto its concrete foundation – thus generating stresses whose amplitude and direction vary depending on the attraction’s own kinematic system. Often these stresses change back and forth between high positive and high negative values, generating huge stresses (both tear and compression stresses) that really put the anchor rods to the test. This is why the professional who prepares the project for the concrete foundations has to know perfectly all the characteristic work cycles of that attraction. Leaving the responsibility for such a delicate phase with the client may cause huge risks, because even a professional may not understand the measure of the stresses generated in the anchor rods, if he or she has no specific experience.

The shape and material for the anchor rods that anchor the attraction to its concrete foundation must therefore be chosen very accurately. The steel that is normally used for construction is not suited to withstand these stresses. If the attraction generates important transverse stresses (i.e. parallel to the ground) normal anchor rods are not sufficient (their screw system is not suited to withstand such forces) and different solutions need to be found. The quality of the concrete to be used for the foundation and for the fill under slab must be chosen with care and following the points mentioned above. There are different types of concrete, with different resistance to pressure and different maturation times. Moreover, the utmost care must be given during the foundation building phase and the attraction installation phase on the construction site to the correct execution and to verifying that all of the project’s specs are followed perfectly.

Finally, we should underline that it is important to check the state of the anchor rods yearly, which is normally done with an ultrasound system. This is a comparative test, therefore the attraction builder should leave one specimen of the anchor rods on the attraction itself, to allow results to be compared to it. What we said up to here is a summary of details that need to be taken care of as a whole by a very experienced professional. Just one mistake in installation may cause bigger stresses to the anchor rods, and this, combined with the possible corrosion effects, may lower the rod’s fatigue resistance even by 50%, causing sudden breakages that are difficult to foresee. Therefore, I recommend to all builders to exercise the utmost care and caution while designing for these phases, and at the same time I recommend to all operators to carry out a yearly NDT test on all of the anchor rods of any big attraction.

 

 

 

Written by Mr. Enrico Fabbri enrico@fabbrirides.com
Article originally published in Games Industry (Italy) magazine
Original date: February 2016

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