Export of Nonlinear Stiffness
In the case of a reinforced concrete model represented as a mixed structure consisting of surface and member elements, the design is carried out in different modules.
The nonlinear calculation of deformations in cracked section (state II) can be considered in both the RF-CONCRETE Surfaces and RF-CONCRETE Members add-on modules. In order to eventually represent the deformation of the entire structure, it is necessary to enable the consideration of the resulting stiffnesses between the modules.
For this, there is a function for exporting the stiffness, which is to be selected under Settings for Nonlinear Calculation in the module. Before this, you have to activate the stiffness export function for the respective load cases or load combinations under Extra Options in RFEM.
There are two options for exporting:
- Individual: The stiffness export is applied only for a load case or load combination with previously determined stiffness.
- Consistent for reference load: The stiffness export is applied for all load cases or load case combinations. So the stiffness to be exported depends on a specific load, which has to be previously selected.
Dipl.-Ing. (FH) Adrian Langhammer
Product Engineering & Customer Support
Mr. Langhammer is responsible for the development of the add-on modules for reinforced cocrete, and provides technical support for our customers.
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Different methods are available for calculating the deformation in the cracked state. RFEM provides an analytical method according to DIN EN 1992-1-1 7.4.3 and a physical-nonlinear analysis.
RFEM add-on module RF-CONCRETE NL | Nonlinear reinforced concrete calculation for the serviceability limit state
Window '1.1 General Data' for Serviceability Limit State with Settings for Nonlinear Calculation According to 
Required reinforcement for rib and axial force distribution, wall taking into account the construction stages
The material model Orthotropic Masonry 2D is an elastoplastic model that additionally allows softening of the material, which can be different in the local x- and y-direction of a surface. The material model is suitable for (unreinforced) masonry walls with in-plane loads.
- I obtain different results when comparing the deformation analysis in the RF‑CONCRETE add-on modules and another calculation program. What could be the reason for this?
- Is it possible to set the parameters for the shrinkage and creeping calculation in RF‑CONCRETE Members?
- Can I simulate the cracked state of a concrete cross-section for a bending beam with the "Isotropic Nonlinear Elastic 1D" material model?
- Why do I get such a small amount of reinforcement for the upstand beam? The amount of reinforcement for the downstand beams is significantly larger.
- How can I display the vertical deformation of a column in state II? I cannot find this setting for the serviceability limit state design.
- What information is transferred when exporting the nonlinear stiffness? Can I display the exported values graphically?
- Is it also possible to perform a deformation analysis in cracked state for a 2D model in RF‑CONCRETE Surfaces?
- When converting from the manual definition of reinforcement areas to the automatic arrangement of reinforcement according to Window 1.4, the result of the deformation calculation differs, although the basic reinforcement has not been modified. What is the reason for this change?
- What is the purpose of the function "Design of longitudinal reinforcement for percentage of utilization" in the setting for nonlinear calculation in RF‑CONCRETE Members? I have selected this option but the structural system is unstable anyway. Why?
- For the design, I can only select the surrounding reinforcement for a rectangular cross-section. Why?