Is it possible to perform the form-finding of membranes regardless of the semi-rigid supporting structure?

Answer

Generally, the form-finding process in RFEM always considers all model data. In form-finding, the elastic supporting elements on the membrane react with the deformations in the direction of the membrane tensile stress acting. The integral process gives the prestressed model to the subsequent calculation if the forces of all deformed elements are in equilibrium with the membrane geometry subjected to the specified prestress.


Figure 01 - Form-Finding with Deformed Supporting Structure

However, the flexibility of the supporting structure can be suppressed for the pure form-finding by defining the support with the "Form-finding stage only" nonlinearity (also called form-finding support) at the membrane edges.


In this case, the form-finding process results in a shape whose prestress is in equilibrium with the specified form-finding support forces and the remaining boundary conditions.


For the structural analysis of all other load cases and combinations, the form-finding supports are deactivated, and the form-finding support forces are applied as external loads to keep the global equilibrium on the entire model.

Due to the removal of the supports, the membrane reacts with the semi-rigid supporting structure in the subsequent analyses (LC and CO). Without additional loading, this reaction is similar to the relaxation with the associated reduction of prestress.




Keywords

Form-finding Support Substructure Supporting structure Flexibility Prestress Membrane

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RFEM Main Program
RFEM 5.xx

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Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

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RF-FORM-FINDING 5.xx

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Form-finding of tensile membrane and cable structures

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