Why does the form-finding process for a conical membrane arrangement not find a continuous, anticlastic design about the principal axis?


The RF-FORM-FINDING add-on module has two form-finding types that you can alternatively assign to each start surface input.

The first option called “Standard” moves the relevant FE nodes in all three spatial directions X, Y, Z until the membrane's constant, specified surface tension is in equilibrium with the boundary reactions.

The second option “Projection” keeps the relative horizontal X', Y'-position of the FE nodes in relation to the normal plane of the surface tension relation axis and only displaces the vertical Z'-Position perpendicular to the plane until the surface tension modified by the membrane is in equilibrium with the slope Peripheral reactions is completed.

In general, the “Standard” method is the right choice for all non-tapered models. In the case of tapered membrane shapes, using the standard method results in an ambiguous situation. In this case, the tangential stress component of the surface tension is mutually exclusive due to the circular arrangement and displaces all FE nodes, irrespective of the radial position and surface stress magnitude, to reach the global equilibrium with consideration of the radial prestress component on the cone axis. In this case, the Projection method must be selected to achieve a continuous conical shape. The resulting shape then holds a non-uniform final surface tension due to the projected surface tension specification.


conic radial tangential projection


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RFEM Tensile Membrane Structures

Add-on Module

Form-finding of tensile membrane and cable structures

Price of First License
1,750.00 USD