Nonlinear Design Method
Performing a design according to the Nonlinear method requires a license of the add-on module RF-CONCRETE NL. This method is described in chapter 2.8. A physical and geometric nonlinear calculation is performed.
Note
The nonlinear design method acts on the assumption of an interaction between model and loading, requiring a clear distribution of internal forces. Therefore, only load cases and load combinations can be analyzed, but result combinations (RC) cannot. In a result combination, two values are available for each FE node – maximum and minimum.
The internal forces for the nonlinear design are generally determined according to the second-order analysis.
Die Schaltfläche [Dialog öffnen] öffnet einen Dialog, in dem die Nachweisparameter überprüft und bei Bedarf angepasst werden können. This dialog box is divided into the Options and Material Properties tabs.
Tools
Options
Dieser Abschnitt steuert, welche Nachweise im Grenzzustand der Gebrauchstauglichkeit zu führen sind:Verformung, Rissbreiten sowie Beton- und Stahlspannungen.Mindestens eines der vier Kontrollfelder muss angehakt sein.
You can also decide if the influence of creeping and shrinkage should be considered in the nonlinear calculation.
Detailed settings for the individual checks as well as for creep and shrinkage are specified in window 1.3 Surfaces (see chapter 3.3.2).
Export of Nonlinear Stiffness
The settings in this dialog section influence the process of the nonlinear design method. You can find more information in chapter 2.8.2.4.
![[Details] Buttons](/en/webimage/054096/4220024/die_[Details]-Schaltflächen.png){kind=small}
When modifying the precision of iterations, make sure that the Maximum number of iterations is higher than the point in the calculation process from which the deformation criterion is additionally taken into account. Click the [Details] button to open the Calculation Parameters dialog box of RFEM. In it, you can adjust the precision of the convergence criteria for the nonlinear calculation.
Bei der nichtlinearen Berechnung wird die Fläche in sogenannte Schichten (Layer) aufgeteilt (siehe Kapitel 2.8.2.1). The recommended number of layers is 10.
Furthermore, you can influence the convergence behavior with Damping: Damping controls the magnitude of the stiffness change in the subsequent calculation steps. For example, if you specify a damping of 50 %, the change of the stiffness between step 2 and 3 can at most be 50 % of the stiffness change between step 1 and step 2.
Material Properties
Material Properties of Reinforcing Steel
Das Kontrollfeld steuert, ob im plastischen Bereich der Spannungs-Dehnungslinie des Betonstahls mit einem ansteigenden oder mit einem horizontalen Ast gerechnet wird (siehe Kapitel 2.8.3.4).
Material Properties of Concrete
In this dialog section, you can specify the stress-strain relations of the concrete in compression and in tension. A parabolic diagram for compression and tension stiffening for concrete tensile stresses is preset.
For Tension stiffening (consideration of the stiffening effect of concrete in the tension zone), you can specify the parameters used to apply the concrete tensile strength between the cracks in a separate dialog box. To open it, click the [Edit] button.
Modifications of the parameters are immediately displayed graphically in the diagrams.
The approach of Tension Stiffening is described in chapter 2.8.3.3.