 # Frequently Asked Questions (FAQ)

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• ### Is it possible to perform a seismic analysis with the masonry material model?

New FAQ 003445 EN

#### Answer

The RF- / DYNAM Pro - Equivalent Loads add-on module only contains a linear analysis of structures. If you now apply a nonlinear model for the calculation, RF- / DYNAM Pro - Equivalent Loads will modify it internally and treat it as a linear model. The nonlinearity in your model is the masonry, which can not absorb tensile forces.

The problem is that: RF- / DYNAM Pro - Equivalent Loads linearly calculates the equivalent loads and exports the load cases from them. However, the load cases are subsequently calculated nonlinearly on the basis of the material model, which is not entirely correct. In addition, the results are superimposed according to the SRSS or CQC method, which results in tensile and compressive forces being present in the model.

In this case, you could, for example, change the masonry to isotropic linear and work with linear properties of the material model. In addition, you could introduce line hinges at this location, which you can use to avoid moment restraint, for example.

• ### How does the material model "Orthotropic Plastic" work in RFEM?

New FAQ 003411 EN

#### Answer

The material model according to Tsai-Wu 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 Tsai-Wu 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 six-dimensional space of tension.
If one of the three stress components is applied as a constant value, the surface can be projected onto a three-dimensional stress space. Projection of yielding surfaces for normal stresses according to Tsai-Wu 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 ideal-plastic, which means no stiffening takes place.
• ### How does the license distribution work for a network dongle in the RF-MAT NL add-on module?

FAQ 003113 EN

#### Answer

When creating a material that has been assigned a nonlinear material model, the license for RF-MAT NL is used. The license is not released until you close the file or change the material model. The license is therefore used for the entire duration, even if no calculation is carried out.

• ### In an RFEM model with a plastic material model, how is it to be determined which plastic deformation remains after the relief?

FAQ 003031 EN

#### Answer

You can do this with the RF-LOAD-HISTORY add-on module.

It is important that the material model "Plastic 2D / 3D" or "Plastic 1D" is used. How does it work ? Dlubal info tags shown.

• ### Where is the modulus of elasticity calculated for the material model damage?

FAQ 002990 EN

#### Answer

The modulus of elasticity is calculated for each step of the defined diagram according hooks law ε=σ/E.

The modulus of elasticity is displayed on the right side of the diagram (picture 1).
• ### I have purchased the add-on module RF-MAT NL, but I can not find it anywhere.

FAQ 002850 EN

#### Answer

The add-on module RF-MAT NL is already integrated in RFEM 5. It is assumed that the following material models can be used:

Isotropic Plastic 1D
Isotropic Plastic 2D/3D
Isotropic Nonlinear Elastic 1D
Isotropic Nonlinear Elastic 2D/3D

Orthotropic plastic 2D
Orthotropic 3D plastic

Isotropic Masonry 2D

Isotropic damage 2D / 3D
• ### Do I have to calculate according to the second-order or large deformation analysis when using plastic material?

FAQ 002615 EN

#### Answer

No, it is not absolutely necessary to calculate according to the second-order or large deformation analysis when using a nonlinear material model. The material nonlinearity is also considered in the case of the calculation according to the linear static analysis.

The calculation according to the second-order analysis or the large deformation analysis means that the equilibrium is set on a deformed structure. So it is geometric nonlinearity.

The difference between the second-order and large deformation is that large rotation may occur in the case of the large deformation analysis.

Thus, if there is no stability problem or if the stability problem is further analysed, the calculation according to the linear static analysis is sufficient.

• ### How can I consider a door lintel made of sectional steel in my wall surface?

FAQ 002319 EN

#### Answer

The easiest case is the door lintel modelled directly on the line of the door opening without an offset. It is then necessary to generate extensions on the wall sides. In the end, the lintel thus consists of three members, as shown in Figure 01.

• ### When defining the material as "Isotropic Masonry 2D", I receive an error message saying the authorization of the program failed.

FAQ 002054 EN

#### Answer

In order to use the "Isotropic Masonry 2D" material, the RF‑MAT NL add-on module has to be licensed. Without the RF‑MAT NL license, only the material models "Isotropic linear elastic" and "Orthotropic elastic 2D/3D" are available.

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