# How can I enter the torsional rigidity (cross-section deformation) in the rotational restraint? I cannot find them anywhere in the program.

Cross-section deformations can be activated or deactivated in the parameters of members and sets of members (see Figure 01). The cross-section deformation is calculated according to EN 1993‑1‑1 as follows:

$\frac{\displaystyle1}{\displaystyle{\mathrm C}_{\vartheta,\mathrm k}}=\;\frac{\displaystyle1}{\displaystyle{\mathrm C}_{\mathrm{ϑR},\mathrm k}}\;+\;\frac{\displaystyle1}{\displaystyle{\mathrm C}_{\mathrm{ϑC},\mathrm k}}\;+\;\frac{\displaystyle1}{\displaystyle{\mathrm C}_{\mathrm{ϑD},\mathrm k}}$

After the calculation, the value is displayed in result tables (see Figure 02).

The information about calculating the value can be found in the relevant literature or in the manual for the RF-LTB add-on module.

#### Reference

 [1] Manual RF-/STEEL EC3- (2020). Tiefenbach: Dlubal Software. [2] Handbuch RF-BGDK. (2011). Tiefenbach: Dlubal Software.