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Internally, for the nonlinear calculation method, the cross-section is meshed, with different materials assigned to individual elements (reinforcement and concrete), and the individual concrete elements can assume different stiffnesses during the calculation (cracking of the concrete).
The FE mesh for the nonlinear analysis can be viewed and its mesh fineness controlled in the cross-section dialog. The following figure shows the corresponding input dialog.
Surfaces
Internally, for the nonlinear calculation method, the FE element is represented in layers, with different materials assigned to individual layers (reinforcement and concrete), and the individual concrete layers can assume different stiffnesses during the calculation (cracking of the concrete).
Integration Methods
The standard integration method for surfaces in RFEM is a Gauss-Lobatto quadrature with nine integration points. This default setting is sufficient for most cases. To adequately capture particularly nonlinear stress-strain curves, it can be useful to increase the number of integration points. Therefore, when using nonlinear material, it is possible to customize the number of integration points in each layer between three and 99 points. However, note that a higher number of integration points is associated with a longer calculation time.
The following three different integration methods are available for selection.
- Gauss-Lobatto Quadrature
- Simpson's Rule
- Trapezoidal Rule
A detailed description of the integration methods can be found in the manual for multilayered surfaces in the linked chapter below Theory of Integration Methods.
The integration method can be defined in the thickness of the surface. The following figure shows the corresponding input dialog.
An overview of the methods based on an example is provided in the technical article Influence of Various Integration Methods on Calculation of Steel Fiber-Reinforced Concrete Slab .