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Why does the calculation after changing surface stiffnesses into "Without membrane tension" take a long time? How are they calculated?


The stiffness type "free of membrane tension" describes the plate and plate stiffness of surfaces.

The plate stiffness including the shear stiffness perpendicular to the surface plane is linearly elastic and the plate stiffness in the surface plane is defined nonlinearly elastic with the material model according to "Drucker-Prague" depending on the defined thickness and the assigned material.

In order to ensure that the surface behaves "draft-free" in the pane direction, the nonlinear material model reacts with tensile direct tensile stress fy, t that approaches zero for tensile-stressed elements in combination with a relatively small solidification modulus Ep. For compression forces, however, the elements remain linearly elastic due to a relatively high compression set tension stress fy, c, and react with an unrestricted compression force transmission.

Since the "membrane-free" stiffness type fundamentally modifies the slice degrees of freedom of surfaces, it is only offered for surfaces in the relevant model types 3D, 2D-XZ (uX / uZ / φY) and 2D-XY (uX / uY / φZ).

To better describe the partial nonlinearity of this surface stiffness type, the release "RFEM 5.06.1103" on 4.02.2016 renames the type from "Without Tension" to "Without Design".


Membrane without tension Without tension Masonry


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