# Frequently Asked Questions (FAQ)

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• ### Is it possible to perform fire resistance design of cross-laminated timber panels in RF‑LAMINATE?

#### Answer

Fire resistance design is not implemented in the RF‑LAMINATE add-on module by default.

However, you can calculate the charring rates yourself and consider them accordingly in the module. In the following example, this is explained on a simple plate.

Structural system (Figure 01):

• Span 5 m
• Plate width 2 m
• LC1 (permanent) 1 kN/m² plus dead load
• LC2 (medium) 2.5 kN/m²
• 3 layers
• S1 35 mm C24
• S2 20 mm C24
• S3 35 mm C24
The information regarding the correction factors and stiffnesses can be found in the attached file.

Factors for fire resistance:

• Charring rate ß0 = 0.65 mm/min
• Pyrolysis zone k0d0 = 7 mm
• Charring time t = 30 min
• Effective thickness def=t ß0+k0d0=30 min × 0.65 mm/min+7 mm = 26.5 mm
Remaining thickness of Layer 3 = 35 − 26.5 = 8.5 mm > 3 mm → thickness may be applied. (Figure 02)

Because of the modified layer thicknesses, a new stiffness matrix results, which is applied in RFEM for accidental combinations with the characteristic stiffness values. For the ultimate limit state, the design values are calculated here (Figure 03).
• ### Is it possible to perform a detailed analysis of connections, supports, or reinforcements of cross‑laminated timber plates in RF‑LAMINATE?

#### Answer

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:

• ### Does the RF‑LAMINATE program consider the shear correction factor for cross-laminated timber plates?

#### Answer

The shear correction factor is considered in the RF‑LAMINATE add-on module by using the following equation.

$k_{z}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{\left(\int_{-h/2}^{h/2}E_x(z)z^2\operatorname dz\right)^2}\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz$

with $\int_{-h/2}^{h/2}E_x(z)z^2\operatorname dz=EI_{,net}$

The calculation of shear stiffness can be found in the English version of the RF-LAMINATE manual, page 15 ff.

For a plate with the thickness of 10 cm in Figure 01, the calculation of the shear correction factor is shown. The equations used here are only valid for simplified symmetrical plate structures!

 Layer z_min z_max E_x(z)(N/mm²) G_xz(z)(N/mm²) 1 -50 -30 11,000 690 2 -30 -10 300 50 3 -10 10 11,000 690 4 10 30 300 50 5 30 50 11,000 690

$\sum_iG_{xz,i}A_i=3\times0.02\times690+2\times0.02\times50=43.4N$

$EI_{,net}=\sum_{i=1}^nE_{i;x}\frac{\mbox{$z$}_{i,max}^3-\mbox{$z$}_{i,min}^3}3$

$=11,000\left(\frac{-30^3}3+\frac{50^3}3\right)+300\left(\frac{-10^3}3+\frac{30^3}3\right)$

$+11,000\left(\frac{10^3}3+\frac{10^3}3\right)+300\left(\frac{30^3}3-\frac{10^3}3\right)+11,000\left(\frac{50^3}3-\frac{30^3}3\right)$

$=731.2\times10^6 Nmm$

$\int_{-h/2}^{h/2}\frac{\left(\int_z^{h/2}E_x(z)zd\overline z\right)^2}{G_{xz}(z)}\operatorname dz=\sum_{i=1}^n\frac1{G_{i;xz}}\left(χ_i^2(z_{i,max}-z_{i,min})\;χ_iE_{i,x}\frac{z_{i,max}^3-z_{i,min}^3}3+E_{i,x}^2\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)$

$χ_i=E_{i;x}\frac{z_{i,max}^2}2+\sum_{k=i+1}^nE_{k;x}\frac{z_{k,max}^2-z_{k,min}^2}2$

 χ1 13.75 106 χ2 8.935 106 χ3 9.47 106 χ4 8.935 106 χ5 13.75 106

$\sum_{i=1}^n\frac1{G_{i;yz}}\left(χ_i^2(z_{i,max}-z_{i,min})-χ_iE_{i,y}\frac{z_{i,max}^3-z_{i,min}^3}3+{E^2}_{i,y}\frac{z_{i,max}^5-z_{i,min}^5}{20}\right)=$

 8.4642 1011 3.147 1013 2.5 1012 3.147 1013 8.4642 1011

Total 6.7133 x 1013

$k_z=\frac{43.4}{{(731.2e^6)}^2}6.713284\;e^{13}=5.449\;e^{-3}$

$D_{44}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{k_z}=\frac{43.4}{5.449\;e^{-3}}=7,964.7 N/mm$

This corresponds to the resulting value in RF‑LAMINATE (Figure 02).
• ### In spite of having defined average regions, they are not considered in the design in RF‑LAMINATE Surfaces. Which setting did I overlook?

#### Answer

In order to consider the average regions in the design in RF‑LAMINATE Surfaces, it is always necessary to activate them in the detailed settings of the add-on module. See Figure&nbso;01 with the detailed settings in RF‑LAMINATE.
• ### What is the meaning of "Shear failure in glued contact surface" in the details of the RF‑LAMINATE add-on module?

#### Answer

In the case of the cross-laminated timber plates that are not glued to the narrow sides, and a wall-like structural behavior, the torsion stress in the glued joints is often governing. This design is performed according to the following equation in compliance with the explanations in the literature reference below.

$\eta_x=\frac{\tau_{tor,x}}{f_{v,tor}}+\frac{\tau_x+\tau_{xz}}{f_R}=\frac{\displaystyle\frac{3\ast n_{xy}}{b(n-1)}}{f_{v,tor}}+\frac{{\displaystyle\frac{\frac{\partial n_x}{\partial x}}{n-1}}+\tau_{xz}}{f_R}\leq1$

where
• b is the board width,
• n is the number of board layers,
• nxy is the shear in the layer plane,
• $\frac{\partial n_x}{\partial x}$ is the shear of board layers,
• $\tau_{xz}$ is the shear in the thickness direction,
• fR is the rolling shear strength,
• fv,tor is the torsional shear strength.
For the y-direction, the design is similar, but with the values for the y‑direction.
• ### What is the meaning of Note 40162 concerning the shear strengths of the Binderholz company?

#### Answer

In the case of the structures by the manufacturer Binderholz, the shear strengths are calculated according to the following equation as soon as the slabs are defined without glue at narrow sides and the design of shear failure is calculated in the wall plane.

$f_{v,k}=\left\{\begin{array}{l}\begin{array}{c}3.5\\8.0\frac{D_{net}}D\\\end{array}\\2.5\frac{(n-1)(a²+b²)}{6Db}\end{array}\right.$

where
D is the element thickness,
Dnet is the sum of the longitudinal and transverse layer thicknesses in the element,
n is the number of board layers,
a = b is the width of the boards in the longitudinal or transverse layers.

All values are in N/mm². For more detailed information, check the manufacturer's approval.
• ### What are the stiffness reduction factors k33 and k88 in RF‑LAMINATE?

#### Answer

These factors reduce the torsional stiffness D33 as well as the shear stiffness D88 of the corresponding stiffness matrix elements of a surface. Since cross-laminated timber is generally not glued at the narrow side, it is also not possible to transfer shear stresses to the timber narrow sides. Thus, the stiffness would be overestimated in this case. For this reason, the stiffness must be reduced accordingly.

Some manufacturers have already provided us these values when delivering the layer structures. They result from the internal analysis. The explanation for determining the correction factors is covered in [1]. The analysis of this work has also been included in the Austrian Annex to EN 1995‑1‑1 [2]. The result is shown in Figure 02. The ratio of the timber width (a) to the timber thickness (ti) can be taken from the respective approval.
• ### Is it possible to create a second design case in RF‑LAMINATE?

#### Answer

No, it is unfortunately not possible.

The layer structure is assigned to certain surfaces in RF‑LAMINATE.

The respective surface obtains then the stiffness defined by this layer structure for the determination of internal forces in RFEM.

If you want to perform a calculation with different layer structures, you have to do it in a copy of the file (another model with different layer structure).

• ### How is it possible to display the main support direction graphically in RF‑LAMINATE?

#### Answer

###### Displaying Main Support Direction in RF-LAMINATE Add-on Module
While entering data in the RF‑LAMINATE add-on module, there is an option to graphically control the orthotropic direction of each individual layer. To do this, simply place the cursor in the desired row of the corresponding position. Then, a coordinate system is displayed in the surface in the RFEM model (see Figure 01). This is to be interpreted as follows:

red axis = x-axis = β-value of the corresponding layer

Generally, the outer layers specify the main support direction, which is why it is sufficient to only consider the first layer. The red axis specifies the primary load-bearing direction (see Figure 01).

###### Displaying Main Support Direction in RFEM
However, the main support direction can also be interpreted directly in RFEM. For this, you can display the local axis systems of the surfaces in detail (see Figure 02). The orthotropic direction β refers to the local x‑axis of the surface. For the example shown in Figure 03, it has a consequence that the main support direction for the left surface runs from one support to another and the secondary surface direction to the right surface. If you want to change the support direction for the right surface, it is possible to either rotate the local surface axis system (see Figure 04) or create a new structure and rotate the orthotropic direction β by 90° (see Figure 05).

If the main support direction is not clearly evident, it is worth taking a look at the stiffness matrix of the surface (see Figure 06). There, it is possible to find the "principal" support direction by means of the bending stiffness, for example. The element D11 refers to the local x‑axis of the surface and the element D22 refers to the local y‑axis of the surface.

• ### Is it possible to save the structures of the manufacturer-specific cross-laminated timber plates in the RF‑LAMINATE add-on module?

#### Answer

The manufacturer-specific structures of cross-laminated timber products are saved in the central library of RF‑LAMINATE.

This library is continuously extended and maintained from our side.

If a manufacturer is supposed to be added in the library, a sample file can be requested from us to save its structures. Furthermore, it is helpful if the manufacturer provides us with the information on the reduction factors of torsional and shear stiffness, the bonding of narrow sides, and so on.

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#### 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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