Continued...
Under normal operating conditions the rubber will not contact the
bronze surface, and the gap between the ribs and the surface will increase over
time as the rubber naturally decays away. In all cases no visible distortion
could be allowed and load cases where the cone cooled and contracted onto the
rib supports needed particular attention.
The cone supports needed to be flexible to allow the bronze to
expand and contract, but they also needed to prevent lifting off of the cone.
When analysing the pressure on the cone surface as wind blew over the
distinctive shape, it was found that large areas of suction could occur on the
surface, creating considerable upwards forces on the structure.
Flexible, strong supports were fitted beneath the cone surface
around the base of the structure at regular intervals, providing a ring of
supports. The supports were designed to provide some springiness in the radial
direction to allow expansion and contraction of the cone, but also provide firm
support in the vertical direction to prevent lift off. The supports are entirely
contained by the bronze shell, and therefore cannot be seen from the outside of
the cone, creating no detraction from the pure geometric shape.
The supports are designed to be entirely invisible to a
viewer, under all loading conditions. The carefully designed supports remain
unnoticed, however they are the key for providing the smooth, undeformed conical
shape, pointing constantly towards the North Star.
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