# Are the surfaces calculated as torsionally flexible or torsionally stiff plates in RFEM?

The surfaces are considered in the calculation as torsionally stiff objects by default.

In the Modify Stiffness tab of the "Edit Surface" dialog box, it is possible to assign "multiplication factors" to a surface for each stiffness matrix element (see Figure  01). By reducing the coefficient k33 , the torsional stiffness can be controlled individually.

For orthotropic surfaces, this tab is not available. In this case, the stiffnesses can be adjusted in the "Edit Surface Stiffness - Orthotropic" dialog box (see Figure 02).

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