#### Further Information

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• ### Is it possible to perform a detailed analysis of connections, supports, or reinforcements of cross‑laminated timber plates in RF‑LAMINATE?

In principle, it is also possible to perform detailed analysis in RF‑LAMINATE. In the case of a very high shear distortion, for example, it can be reasonable to use orthotropic solids for modeling. The video shows a simple modeling and result evaluation of a layer structure by using solids.

A criterion, as of when is the modeling using solids useful, is the shear correction factor. Further information and other criteria can be found in the following FAQ:

• ### Where can I set the Poisson's ratio?

The Poisson's ratio is set under the material by using the Edit Material dialog box.
• ### When trying to calculate the design in RF-STEEL Surfaces, I receive Warning No. 1162 - Surface No. XX is of the type "Orthotropic" and cannot be designed. What does this Warning mean?

Orthotropic surfaces are non-linear and cannot be designed within the RF-STEEL Surfaces add-on module. It is possible to get a full stress analysis in RFEM for the orthotropic surfaces defined with the orthotropy type "constant thickness" and compared to limiting stresses manually. For all other orthotropy type, the program is not aware of the geometric properties for the surface at every FE mesh point which is needed to calculate stresses. An extensive and detailed FE model would need to be created. See FAQ 2468 for an example of this. Surface types need to be set to "standard" to be designed within the add-on module.

• ### When calculating an oblique plate, I obtain very high result values for the line supports at 2 edge nodes. Why is it so and how can I avoid it?

The default definition of surface elements assumes the isotropic material behavior. The load attempts to get to the supports as quickly as possible. The stiffness of the elements also plays a role here.
In the case of plates, the best way to display and represent the structural behavior or the load transfer is to use the trajectories of the principal moments αb. For wall elements, it is necessary to consider the trajectories of the principal axial forces αm.
In this example, the load is not transferred parallelly to the free edges of the plate, but almost perpendicularly to the supports as this is the shortest path of the load transfer.
At the dulled corners of the structure, the load application area is larger than in the support centers, corresponds to a singularity point, and as a consequence of that, it has great peak values.
In order to force the system to remove the load parallel to free plate edges, the following procedure is the fastest:
Definition of an orthotropic plate. It is recommended to use the "Effective Thicknesses" orthotropy type. The effective plate thickness has to be specified in the support direction and a very small thickness in the secondary support direction (for example, 1 mm).
The second figure shows the difference between both models.
• ### I cannot define the prestress separately for warp and weft in RF‑FORM‑FINDING. How can I activate it?

The warp and weft directions are linked to the axes of the surface. The default setting allows you to only apply isotropic prestress. If the axes are aligned, the orthotropic or radial prestress will be available as well.

The video shows the procedure.

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

The material model according to Tsai-Wu unifies the plastic with the orthotropic properties. In this way, it is possible to specifically model the materials with anisotropic properties, such as 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 Elastic - 3D material model. For the plastic area, the yielding according to Tsai-Wu applies:

${\text{f}}_{\mathrm{crit}}\left(\mathrm\delta\right)=\frac1{\mathrm C}\left[\frac{\left({\mathrm\delta}_{\mathrm x}-{\mathrm\delta}_{\mathrm x,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm x}{\mathrm f}_{\mathrm c,\mathrm x}}+\frac{\left({\mathrm\delta}_{\mathrm y}-{\mathrm\delta}_{\mathrm y,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm y}{\mathrm f}_{\mathrm c,\mathrm y}}+\frac{\left({\mathrm\delta}_{\mathrm z}-{\mathrm\delta}_{\mathrm z,0}\right)^2}{{\mathrm f}_{\mathrm t,\mathrm z}{\mathrm f}_{\mathrm c,\mathrm z}}+\frac{{\mathrm\tau}_{\mathrm{yz}}^2}{{\mathrm f}_{\mathrm v,\mathrm{yz}}^2}+\frac{{\mathrm\tau}_{\mathrm{xz}}^2}{{\mathrm f}_{\mathrm v,\mathrm{xz}}^2}+\frac{{\mathrm\tau}_{\mathrm{xy}}^2}{{\mathrm f}_{\mathrm v,\mathrm{xy}}^2}\right]$

where:

${\mathrm\delta}_{\mathrm x,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm x}-{\mathrm f}_{\mathrm c,\mathrm x}}2$

${\mathrm\delta}_{\mathrm y,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm y}-{\mathrm f}_{\mathrm c,\mathrm y}}2$

${\mathrm\delta}_{\mathrm z,0}=\frac{{\mathrm f}_{\mathrm t,\mathrm z}-{\mathrm f}_{\mathrm c,\mathrm z}}2$

$\mathrm C=1+\left[\frac1{{\mathrm f}_{\mathrm t,\mathrm x}}+\frac1{{\mathrm f}_{\mathrm c,\mathrm x}}\right]^2\frac{{\mathrm E}_{\mathrm x}{\mathrm E}_{\mathrm p,\mathrm x}}{{\mathrm E}_{\mathrm x}-{\mathrm E}_{\mathrm p,\mathrm x}}\mathrm\alpha+\frac{{\mathrm\delta}_{\mathrm x,0}^2}{{\mathrm f}_{\mathrm t,\mathrm x}{\mathrm f}_{\mathrm c,\mathrm x}}+\frac{{\mathrm\delta}_{\mathrm y,0}^2}{{\mathrm f}_{\mathrm t,\mathrm y}{\mathrm f}_{\mathrm c,\mathrm y}}+\frac{{\mathrm\delta}_{\mathrm z,0}^2}{{\mathrm f}_{\mathrm t,\mathrm z}{\mathrm f}_{\mathrm c,\mathrm y}}$

You can imagine the yield criterion as an elliptical surface in a six-dimensional stress space.
If one of the three stress components is applied as a constant value, the surface can be projected onto a three-dimensional stress space. The projection of yield surfaces for normal stresses according to Tsai‑Wu: if the value for fy (σ) is smaller than 1, the stresses rest within the elastic area. The plastic area is reached as soon as fy (σ) = 1; the values greater than 1 are not allowed. The model behavior is ideal-plastic, which means there is no stiffening.
• ### Which material model should be assigned to a timber contact solid?

In the case of timber, the "Orthotropic Elastic/Plastic 3D" material model has to be assigned to the "Material" solid type (Figure 01).

Since the program considers the "Contact" solid type as a member, it usually requires the isotropic material model (Figure 02).

• ### My model includes members and surfaces/solids made of wood. I have already created the orthotropic material model 2D/3D. Now, I receive the error message saying that the material model for the cross-section X must be isotropic.

In this case, the orthotropic material model is probably assigned to both the surfaces/solids and the members. However, timber members require an isotropic material model. Therefore, it is necessary to create another timber material and assigned it to the corresponding members or cross-sections.

• ### Where can I find the stiffness matrices of orthotropic surfaces?

In the case of user-defined matrices, the stiffness matrices of orthotropic surfaces are saved in the MatrixConstants.cfg file in the C:\ProgramData\Dlubal\Global\General Data folder. The folder requires the standard installation!
• ### How can I define failure criterion s such as Tsai-Wu for orthotropic material?

If you want to define failure criterion s for orthotropic material you have to define a orthotropic plastic material in the Material Model (picture 1).

The yield criterion will be done according the Tsai-Wu criterion (picture 2).

By this Link you can find 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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#### 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 stand-alone 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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