Post-Tensioned Modular Inflated Structures 227 air-inflated meridian paralel cushions cables cables Fig.7.Construction of synclastic air-inflated modular shell 4 Adjustment of Rigidity and Hardening Systems 4.1 Structures with Variable Rigidity Curvature of air-inflated shells formed in self-erection process can be con- trolled by means of changing their rigidity along the span [6].It is an ef fective way of shaping this kind of structures,which allows fulfilment of the requirements.Initial stiffness of inflated shell is defined mostly by its struc- tural height.The change of height causes the change of stiffness.This can be achieved in two ways: either by use of additional rods,i.e.cross-braces,moving tension cables down from the cushions or by change of cushions'thickness Figure 8 presents those two methods. cushions with variable thickness cross-braces with variable length Fig.8.Methods of rigidity alteration in modular shells Two compared shells,of the same initial length and subjected to the same upthrust,i.e.nearing of supports,but with various,variable rigidities,demon- strate distinctly different final geometry.If the rigidity of the shell is increased in the central part-the curvature is smaller in the center than in peripheres (structure is more flat).On the other hand-the curvature is smaller on sides, when rigidity is decreased in the central part of the shell(structure is morePost-Tensioned Modular Inflated Structures 227 Fig. 7. Construction of synclastic air-inflated modular shell 4 Adjustment of Rigidity and Hardening Systems 4.1 Structures with Variable Rigidity Curvature of air-inflated shells formed in self-erection process can be con￾trolled by means of changing their rigidity along the span [6]. It is an ef￾fective way of shaping this kind of structures, which allows fulfilment of the requirements. Initial stiffness of inflated shell is defined mostly by its struc￾tural height. The change of height causes the change of stiffness. This can be achieved in two ways: – either by use of additional rods, i.e. cross-braces, moving tension cables down from the cushions – or by change of cushions’ thickness Figure 8 presents those two methods. Fig. 8. Methods of rigidity alteration in modular shells Two compared shells, of the same initial length and subjected to the same upthrust, i.e. nearing of supports, but with various, variable rigidities, demon￾strate distinctly different final geometry. If the rigidity of the shell is increased in the central part – the curvature is smaller in the center than in peripheres (structure is more flat). On the other hand – the curvature is smaller on sides, when rigidity is decreased in the central part of the shell (structure is more