The Atomium's central tube, 10.8 ft in diameter, is 348 ft long and made up of cylindrical steel ferrules of 12mm thickness up to a height of 197 ft, and of 6 mm thickness the rest of the way to the top. The steel plates, which are arched and welded, are reinforced internally, first by 12 strong angle bars 7.87 in. by 7.87 in. in high grade steel forming a hexagon at the vertex of which they are joined by twos, secondly by longitudinal and transversal stiffeners which prevent any buckling of the outer ferrule. This central column is highly resistant to compression and flexion stresses. The 348 ft high mast is made up of several sections the lenghts of which vary from 10 to 39 ft. The circular space within is entirely occupied by the lift, its guide-rails and counterweights. The base of the mast is 10 ft below ground-level.

The central mast weighs approximately 1.81 ton per yard in the first half, and 1.35 ton per yard from the middle of the central sphere to the top.

The other linking tubes between spheres differ structurally from the central mast by one point: the strong longitudinal angle bars are suppressed, the ferrule is only 6 mm thick and the weight of those tubes is only 0.9 ton per yard. All the tubes linking the outer spheres are 9.84 ft diameter, while the diagonal ones, i.e. those linking the outer spheres with the central one, are 10.82 ft in diameter. The reason for this difference is that it has been endeavoured to reduce the tube diameters as much as possible for esthetical reasons. When these were steeply inclined, as it is the case for the outer tubes, their vertical section, with a 9.84 ft diameter, is sufficient for passage, even in the case of the tube containing an escalator.

For the diagonal links, the slope of the tubes - which is only 19° to the horizontal - necessitates a 10% increase of diameter, otherwise the free space available between the escalator steps and the tube roofing could have been insufficient.

B. THE SPHERES

The spheres must of necessity have a particularly resistant structure at the tube junctions and it is logical to have a main framework made up of arches supported - in the case of three spheres on the vertical axis - on the central mast. Each sphere has 12 arches. Six highly resistant arches are necessary, in the case of the base sphere, to take the thrust of three tubes; the six others take up the stresses from the floors and from the secondary framework which trusses the 12 arches and supports the skin. In the case of the central sphere, which takes the loads transmitted by four tubes, the twelve arches are all equally resistant.

These arches are made up of entirely closed box spars in 12 mm thick welded high grade steel sheet. The weight of a large arch is about 4,92 tons. The thrust which the tubes transmit to the arches is passed on by two articulations.

There are 6 internally furnished spheres accessible to the public:
- The base sphere.
- The three lower spheres, supported by bipods.
- The central sphere.
- The top sphere.

Each sphere has two main floors and an extra servicing floor in the lower part.

The structure of the Atomium is mainly made up of large and heavy elements, which meant that powerful erecting means had to be provided. For example, the bipods, which support the lower spheres, each weigh about 110 tons. They were assembled on the ground and each put in place as a single piece, lifted by two lifting arms at their centre of gravity.

C. THE BIPODS

Each of the three bipods, weighing over 100 tons, is made up of two enormous triangular box spars, entirely welded, 118 ft long and each weighing 39 tons. The two spars are assembled on the site by bolted joints. A very rigid crossbar links the two main spars at the level of the large landing, which is about 33 ft above ground. The trusses inclined as the stairs are bolted to the two square-section braces which support the landings fitted inside the main spars.