Calculation of Pneumatic Structures - Easy.Vol
The Formfinding procedure and the Statical Analysis of Pneumatic Structures can be performed with Easy.Form and Easy.Stat only as a first approximation because of the fact, that the external loads are conservative loads.
Conservative loads do not change their size and direction during the loading procedure. The internal pressure in Pneumatic Structures is a value depending on the normal vector of the pneumatic system, therefore the use of non-changing conservative loads for the internal pressure can only be an approximation.
In Easy.Vol the internal pressure is changing its direction and size depending on the loaded area. Therefore a precise model is described by Easy.Vol, where the consideration of gas-laws enables the realistic behavior of the internal pressure: only in this case the membrane stresses get the correct size.
Biogas storage systems often have 2 membrane covers. The outer shell and the so-called gas membrane. The air volume between the outer and inner shell is called the air support space. It is always under pressure.
The volume under the gas membrane forms the so-called gas space. There are different pressure situations in the gas space. If the pressure in the gas space is 0, the gas membrane lies
on the belts, which run from a central point to the silo edges. When the gas pressure is maximum, the volume of the gas space becomes maximum and the volume of the air support space becomes minimum.
Easy.Vol allows quick modelling and calculation of the different pressure situations, taking into account the gas law.
Load case calculations can be performed in 3 different modes: Constant internal pressure (p=constant), constant volume (V=constant), constant product of internal pressure and volume (p∙V=constant, Boyle's Law of Gas) or the general gas equation (p∙V/T=constant).
ETFE is very often used for multi-layer, pneumatically supported cushion constructions. With Easy any number of foil chambers can be modelled, statically calculated and cut to size.
Inflatable tube systems combined with mechanically stressed membrane surfaces are difficult to create as mechanical models without the appropriate modeling tools. Such systems are often used in aircraft (hangars) in disaster control or for general industrial applications. Easy provides you with suitable methods and tools for modelling and calculation.
The example shows a tube system as frame for mechanically tensioned membrane walls. It is one chamber, the internal pressure is 0.3 bar. Left static calculation without external loads, right wind load case.
The pneumatically tensioned membrane surface is normally attached to a rigid primary structure. The general interaction between the pneumatically stressed membrane and the primary structure is considered in Easy by a hybrid model. Ignoring the interaction leads to "wrong" results.
Sometimes belts or cables are used for structural reinforcement. In Easy, these elements can be defined as "attached to the membrane" or "lying freely on the membrane".
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