In this tutorial, we would like to inform you about the essential features of the RFEM program. The first part shows how to create the structural objects and loads, combine the loads, perform a structural analysis, check the results, and prepare the data for printing. Eurocodes with the CEN settings are used as standards.
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RFEM 6 | Tutorial - Structural Analysis
RFEM 6 | Tutorial - Structural Analysis
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For reinforced concrete components and structures whose structural behavior is significantly influenced by the second-order effects, Eurocode 2 provides the general method based on a nonlinear determination of internal forces according to the second-order analysis (5.8.6), as well as an approximation method based on the nominal curvature (5.8.8).
The aim of this technical article is to perform a design according to the general design method of Eurocode 2, using the example of a slender reinforced concrete column.
The aim of this technical article is to perform a design according to the general design method of Eurocode 2, using the example of a slender reinforced concrete column.
Using an example of a steel fiber-reinforced concrete slab, this article describes how the use of different integration methods and of a different number of integration points affects the calculation result.
The "Nonlinear Material Behavior" add-on includes the Anistropic | Damage material model for concrete structural components. This material model allows you to consider concrete damage for members, surfaces, and solids.
You can define an individual stress-strain diagram via a table, use the parametric input to generate the stress-strain diagram, or use the predefined parameters from the standards. Furthermore, it is possible to consider the tension stiffening effect.
For the reinforcement, both nonlinear material models "Isotropic | Plastic (Members)" and "Isotropic | Nonlinear Elastic (Members)" are available.
It is possible to consider the long-term effects due to creep and shrinkage using the "Static Analysis | Creep & Shrinkage (Linear)" analysis type that has been recently released. Creep is taken into account by stretching the stress-strain diagram of the concrete using the factor (1+phi), and shrinkage is taken into account as the pre-strain of the concrete. More detailed time step analyses are possible using the "Time-Dependent Analysis (TDA)" add-on.
The "Orthotropic | Fabric | Nonlinear Elastic (Surfaces)" material model allows you to define prestressed fabric membranes using the representative microstructure-solid element model – RVE.
By considering the fabric geometry in the microstructure model, the corresponding transversal strain effect can now be considered for all force conditions in the membrane.
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Are you familiar with the Tsai-Wu material model? It combines plastic and orthotropic properties, which allows for special modeling of materials with anisotropic characteristics, such as fiber-reinforced plastics or timber.
If the material is plastified, the stresses remain constant. The redistribution is carried out according to the stiffnesses available in the individual directions. The elastic area corresponds to the Orthotropic | Linear Elastic (Solids) material model. For the plastic area, the yielding according to Tsai-Wu applies:
All strengths are defined positively. You can imagine the stress criterion as an elliptical surface within a six-dimensional space of stresses. If one of the three stress components is applied as a constant value, the surface can be projected onto a three-dimensional stress space.
If the value for fy(σ), according to the Tsai-Wu equation, plane stress condition, is smaller than 1, the stresses are in the elastic zone. The plastic area is reached as soon as fy (σ) = 1; values greater than 1 are not allowed. The model behavior is ideal-plastic, which means there is no stiffening.
Did you know? In contrast to other material models, the stress-strain diagram for this material model is not antimetric to the origin. You can use this material model to simulate the behavior of steel fiber-reinforced concrete, for example. Further information about modeling steel fiber-reinforced concrete can be found in this technical article: KB | Determining Material Properties of Steel Fiber-Reinforced Concrete and Their Application in RFEM
In this material model, the isotropic stiffness is reduced with a scalar damage parameter. This damage parameter is determined from the stress curve defined in the Diagram. This does not take the direction of the principal stresses into account; rather, the damage occurs in the direction of the equivalent strain, which also covers the third direction perpendicular to the plane. The tension and compression areas of the stress tensor are treated separately. In this case, different damage parameters apply.
The "Reference element size" controls how the strain in the crack area is scaled to the length of the element. With the default value zero, no scaling is performed. Thus, the material behavior of the steel fiber-reinforced concrete is modeled realistically.
You can find the background information on the "Isotropic Damage" material model in this technical article: KB 001461 │ Nonlinear Material Model Damage .