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Answer
In the RF/STEEL addon module, an equivalent stress design is performed according to von Mises. An elastic stress design (ELEL) is to be made. In RF/STEEL EC3, a classification is carried out before the design. If the crosssection is classified as class 1 or class 2, the design is performed against plastic limit internal forces. An ELPL design is performed. If you do not want to use the plastic load reserves, you can switch the design to ELEL in the details of the RF/STEEL EC3 addon module. The results are then comparable with RF/STEEL. 
Answer
The difference between both material models is as follows:
In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state when the load is released.
Whereas in the case of the material model Isotropic Plastic 1D, the plastic deformation is considered.
For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible to define a distribution in both models after the last step.
For the material model Isotropic Nonlinear Elastic 1D, it is possible to enter the stressstrain diagram (different for the positive and negative zone) in an antimetrical way, whereas for the model Isotropic Plastic 1D, only symmetric input is possible.

Answer
Since the equivalent member designs of Eurocode 3 have different interactions than are the case for the designs according to the partial internal forces method and a mixture of these different designs is not desired for reasons of clarity, RFEM deactivates the equivalent member designs when using the RF/STEEL Plasticity addon. 
Answer
The plasticity for 1D elements currently only works in relation to the normal stresses in a member. This means that only interaction between axial force and moment is possible. The shear force interaction is not taken into account. In addition, the stresses from shear force are only calculated elastically.
When applying a plastic material model, it is also important to ensure a sufficient division of the elements, because a crosssection is internally generated at each Gauss point on the member element where the stress is calculated and a reduction of the stiffness to the redistribution of the internal forces is performed, if necessary. If, for example, the number of divisions is increased, the model may become unstable because the redistributions of stresses can no longer be carried out and thus the crosssection's loading is too high.
It is generally recommended to use a division of '50' for member elements when using the plastic material model (see the figure).

Answer
The material model according to TsaiWu unifies plastic with orthotropic properties. This way, you can enter special modelings of materials with anisotropic characteristics such as plastics or timber. When the material is plasticized, stresses remain constant. A redistribution is carried out according to the stiffnesses available in the individual directions. The elastic zone corresponds to the material model Orthotropic  3D. For the plastic zone, the yielding according to TsaiWu applies:${\text{f}}_{\mathrm{crit}}\left(\mathrm\delta\right)=\frac1{\mathrm C}\left[\frac{\left({\mathrm\delta}_{\mathrm x}{\mathrm\delta}_{\mathrm x,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm x}{\mathrm f}_{\mathrm c,\mathrm x}}+\frac{\left({\mathrm\delta}_{\mathrm y}{\mathrm\delta}_{\mathrm y,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm y}{\mathrm f}_{\mathrm c,\mathrm y}}+\frac{\left({\mathrm\delta}_{\mathrm z}{\mathrm\delta}_{\mathrm z,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm z}{\mathrm f}_{\mathrm c,\mathrm z}}+\frac{{\mathrm\tau}_{\mathrm{yz}}^2}{{\mathrm f}_{\mathrm v,\mathrm{yz}}^2}+\frac{{\mathrm\tau}_{\mathrm{xz}}^2}{{\mathrm f}_{\mathrm v,\mathrm{xz}}^2}+\frac{{\mathrm\tau}_{\mathrm{xy}}^2}{{\mathrm f}_{\mathrm v,\mathrm{xy}}^2}\right]$with:${\mathrm\delta}_{\mathrm x,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm x}{\mathrm f}_{\mathrm c,\mathrm x}}2$${\mathrm\delta}_{\mathrm y,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm y}{\mathrm f}_{\mathrm c,\mathrm y}}2$${\mathrm\delta}_{\mathrm z,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm z}{\mathrm f}_{\mathrm c,\mathrm z}}2$$\mathrm C=1+\left[\frac1{{\mathrm f}_{\mathrm t,\mathrm x}}+\frac1{{\mathrm f}_{\mathrm c,\mathrm x}}\right]^2\frac{{\mathrm E}_{\mathrm x}{\mathrm E}_{\mathrm p,\mathrm x}}{{\mathrm E}_{\mathrm x}{\mathrm E}_{\mathrm p,\mathrm x}}\mathrm\alpha+\frac{{\mathrm\delta}_{\mathrm x,0}^2}{{\mathrm f}_{\mathrm t,\mathrm x}{\mathrm f}_{\mathrm c,\mathrm x}}+\frac{{\mathrm\delta}_{\mathrm y,0}^2}{{\mathrm f}_{\mathrm t,\mathrm y}{\mathrm f}_{\mathrm c,\mathrm y}}+\frac{{\mathrm\delta}_{\mathrm z,0}^2}{{\mathrm f}_{\mathrm t,\mathrm z}{\mathrm f}_{\mathrm c,\mathrm y}}$The yielding condition can be thought of as an elliptical surface in a sixdimensional space of tension.If one of the three stress components is applied as a constant value, the surface can be projected onto a threedimensional stress space. Projection of yielding surfaces for normal stresses according to TsaiWu If the value for fy (σ) is smaller than 1, the stresses lie within the elastic range. The plastic zone is reached as soon as fy (σ) = 1; values greater than 1 are not allowed. The model behavior is idealplastic, which means no stiffening takes place. 
Answer
The plastic section modulus for crosssections is implemented in the library. Among other things, it is used for the limiting moments of plastic member hinges. There is also an interesting technical article for this. 
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This is possible with the RF‑LOAD‑HISTORY add‑on module.
It is important to use the "Plastic 2D/3D" or "Plastic 1D" material model. How it works in practice is shown in this recording of a Dlubal Info Day.

Answer
If you want to define failure criterion s for orthotropic material you have to define a orthotropic plastic material in the Material Model (Figure 1).
The yield criterion will be done according the TsaiWu criterion (Figure 2).This Link provides you with a full set of verification examples to this material model.The material model itself is explained in several Knowledge base articles. 
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The addon module RFMAT NL is already integrated in RFEM 5. It is assumed that the following material models can be used:Isotropic Plastic 1DIsotropic Plastic 2D/3DIsotropic Nonlinear Elastic 1DIsotropic Nonlinear Elastic 2D/3DOrthotropic Plastic 2DOrthotropic 3D PlasticIsotropic Masonry 2DIsotropic Damage 2D/3D 
Answer
The RF / ELPL addon module is designed only for the elasticplastic design of steel crosssections. As a result, you can only calculate materials from the "Steel" category in the addon module.
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First Steps
We provide hints and tips to help you get started with the main programs RFEM and RSTAB.
Wind Simulation & Wind Load Generation
With the standalone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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