Material Models
- The material models are the basis for composing multilayer surfaces to obtain an effective surface stiffness. The Multilayer Surfaces Add-on allows you to freely combine the material models in the RFEM 6 program. The basis of the material models is described in Chapters Materials and Nonlinear Material Behavior of the RFEM manual.
- A selection of the possible combinations of the material models is created in the "Multilayer Models" model (see the right column), which you can download for further study of the combinations.
- The following list shows a selection of the possible combinations:
- * Isotropic layers (e.g. concrete - steel)
- * Orthotropic layers (e.g. cross-laminated timber)
- * Isotropic - orthotropic (e.g. steel - GFRP)
- * Isotropic Plastic - Isotropic (e.g. Concrete - Steel)
- * Isotropic Nonlinear Elastic - Orthotropic (e.g. Concrete - Timber)
- * Isotropic - Orthotropic Plastic (e.g. Concrete - Timber)
- * Isotropic Damage - Orthotropic (e.g. Concrete - Timber)
- #banner.textNonlinear Material Behavior should be activated.
- == Stiffnesses for Multilayer Surfaces Without Solids ==
- The simpler calculation option in the Multilayer Surfaces add-on is to define different surface layers in the thickness type 'Layers' without solids. However, you can also freely combine the material models here.
- Once the layers are defined, the Multilayer Surfaces add-on creates a global stiffness matrix of the surface. In RFEM, the internal forces and deformations are calculated for this surface. In the respective design add-on, such as Timber Design or Stress-Strain Analysis, these internal forces are then divided into the existing layers. Usually, the internal forces are displayed as three integration points per position.
- This article explains how to calculate the stiffness matrix for isotropic and orthotropic materials.
- === Calculation of stiffness matrix ===
- The material models are based on the following conditions (see Chapter Materials of the RFEM manual):
- * All stiffness values ≥ 0
- * Overall stiffness matrix of surface must be positive definite.
- * Basic equation isotropic:
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E
modulus of elasticity
G
shear modulus
ν
Poisson's ratio