226 Romuald Tarczewski final position intermediate position initial position tension of the bottom cables Fig.5.Scheme of self-erection procedure air-inflated cushions cables in bottom layer tension of the upper cables cables in upper layer 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 rev- olution in particular,can be achieved in that way.Fig.7 presents such a structure,shaped as a hemisphere,made of hexagonal elements.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 rev￾olution in particular, can be achieved in that way. Fig. 7 presents such a structure, shaped as a hemisphere, made of hexagonal elements