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226 Romuald Tarczewski
Fig. 5. Scheme of self-erection procedure
Fig. 6. Bidirectional post-tensioning of air-inflated shell
cables of the second direction are tensioned to the same value. Finally, the
cables are alternatively rectified, to reach requested values.
3.2 Post-Tensioning Applied to Completed Structure
Another way of assembling is to put cushions in position one by one – as in
an igloo and then tension the cables to stiffen the structure. In that case, shell
must be shaped as a self-stable before post-tensioning is performed. Certainly,
scaffoldings can be used, however, this overthrows the whole system.
Structures with positive Gausian curvature (synclastic), surfaces of revolution
in particular, can be achieved in that way. Fig. 7 presents such a
structure, shaped as a hemisphere, made of hexagonal elements.