It is on this lower ensemble, completed by the framework of the three lower spheres, that the system made up of the three middle spheres and of the top sphere is supported. So as to avoid the difficulties of stress calculations in hyperstatic constructions, two liaisons were abolished by enabling two of the tubes to slide at one extremity on their support. The tubes concerned are a diagonal tube linking the first lower sphere with the central one, and the prolongation of this diagonal towards the middle sphere opposite. In simpler terms for the uninitiated: an equally strong Atomium could be built by simply suppressing two of the tubes that make up a diagonal.

In this special construction, it is only normal that exceptional precautions were taken to check the calculations and to test the welded assemblies. Tests were carried out on the structure itself by applying known loads at selected points and measuring the actual stresses in the steel at certain points. These tests confirmed the exactness of the calculations and the validity of the basic hypothesis.

The measured stresses were always, in fact, in close agreement with the pre-computed stresses, to a very acceptable tolerance. The strain-gauges used for these stress measurements will stay in place and it will thus be possible to continue these when the work is finished and the Atomium in normal use.

Specialised scientific bodies have found these tests most interesting to the future progress of metal construction generally and have brought their help for these technical investigations.