Answer:
The "Without membrane tension" stiffness type describes the plate and plane stiffness of surfaces.The plate stiffness including the shear stiffness perpendicular to the surface plane is defined linearly elastic and the plate stiffness in the surface plane is defined nonlinearly elastic with the material model according to "Drucker-Prager" depending on the defined thickness and the assigned material.
In order to ensure that the surface behavior is "Without tension" in the pane direction, the nonlinear material model reacts with yielding tensile stress fy,t going to almost zero in the elements subjected to tension in combination with a relatively small strain hardening modulus Ep. On the other hand, in the case of compressive forces, the elements remain virtually unaffected linearly elastic due to the relatively high yielded compressive stress fy,c and react with an unrestricted compression transmission.
Since the "Without membrane tension" stiffness type basically modifies the pane-related degrees of freedom of the surfaces, it is only applied to the surfaces of 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, it was renamed from "Without tension" to "Without membrane tension" as of Version RFEM 5.06.1103 on 2.4.2016.
