Why does form-finding warp the membrane surfaces into each other?

Answer

The form-finding warps the surfaces into each other because the defined prestress on the boundary line between the two membranes does not coincide at the same angle and consequently the affected FE nodes are not in equilibrium with the boundary reactions. In this case, the FE nodes of the membrane surfaces move in the direction of the remaining resultant until the form-finding process finds a solution within the tolerance limit value. Since this solution is usually only achievable with a large displacement of the FE nodes in space, the surfaces assigned to the FE nodes seem to 'swim' into each other.

This behavior results in an unfavorable FE mesh arrangement in conjunction with a singular membrane force distribution. In this case, the prestress must be adjusted to reach a balanced position or an element must be arranged at the limit situation to transfer forces from the imbalance.


Keywords

Membrane Warps Prestress Balance Singularity

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RFEM Main Program
RFEM 5.xx

Main Program

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

Price of First License
3,540.00 USD
RFEM Tensile Membrane Structures
RF-FORM-FINDING 5.xx

Add-on Module

Form-finding of tensile membrane and cable structures

Price of First License
1,750.00 USD