Further Information

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

New FAQ 004347 EN

In principle, it is also possible to carry out detailed analyzes with RF-LAMINATE. For example, in the case of a very high shear distortion, it can make sense to carry out the modeling using orthotropic solids. The video shows the simple modeling and result evaluation of a layer structure using solids.

One criterion when modeling over solids is useful is the shear correction factor. Following FAQ contains further information on this and other criteria:

• How can I consider the flexibility of a continuous beam with slotted dowel connections?

New FAQ 004346 EN

The easiest way to consider this is to use the RF-/JOINTS Timber - Steel to Timber module. For this purpose, the module dissolves the original connection and creates a new static system that takes flexibility into account accordingly. This is taken into account separately for the ultimate limit state, serviceability limit state, and accidental.
• Where can I set the Poisson's ratio?

New FAQ 004341 EN

The Poisson's ratio is set under the material by using the Edit Material dialog box.
• When displaying the result diagrams on a member (the "rib" type), there is the option to display the internal force VL. What is this value and how is it calculated?

New FAQ 004340 EN

The force VL is the longitudinal shear force between the top surface and the member. It is calculated as an integrated shear flow between the plate and the member at a particular point on the member.

For the simplified example provided here, the resulting cross-section values for the integration width of 10 cm are as follows:

• $I_y=\frac{b\times h^3}{12}=\frac{10 cm\times20 cm^3}{12}=6,666.67 cm^4$
• $S_y=h_1\times b\times((h-e_z)-\frac{h_2}2)=10 cm\times10 cm\times((20 cm-10 cm)-\frac{10 cm}2)=500 cm^3$
• $\tau=V_L=\frac{V_z\times S_y}{I_y\times b}=\frac{5.53 kN\times500 cm^3}{6,666.67 cm^4}=0.415 kN/cm=41.5 kN/m$
The integration width has been set to the total of 10 cm.

Values:
• Iy second moment of area
• Sy statical moment
• h1 height of the upper cross-section part
• h2 height of the lower cross-section part
• ez centroidal distance
• h total height
The values can be adjusted for a T-beam.
• I am trying to design a mixed structure of timber materials with different creep properties. How can I perform the design for the serviceability according to EN 1995-1-1?

New FAQ 004325 EN

In RFEM and RSTAB, the simplified designs from [1] Chapter 2.2.3 have been implemented for the automatic load combinations. This means that strictly speaking, only structures concerning the final deformation may be analyzed, in which materials with identical creep behavior occur since the creep deformations are considered in a simplified way on the load side. If the structure is a mixed structure made of wood with different creep properties or in combination with steel, the final deformations must be determined according to [2] Amendment to 2.2.3 as follows:

'(4) If a structure consists of structural components or components with different creep properties, the long-term deformations should be calculated according to 2.3.2.2 (1) due to the quasi-permanent combination of actions with the final values of the mean values of the corresponding elasticity, shear, and displacement modules. The final deformation ufin is then calculated by superposition of the initial deformation due to the difference of the characteristic and quasi-permanent combinations of actions with the long-term deformation.'

However, this requires a superposition of results from different load combinations, which cannot be implemented automatically in RFEM and RSTAB.

If the different creep properties are to be taken into account, the load combinations must be created manually, and the stiffness must be reduced according to the creep coefficient.
The procedure is described using the example of a timber-concrete composite floor presented on the Info Day 2017. Below this FAQ, you can find the link for this.

• Is the Gust-effect (G or Gf) from the ASCE 7-16 Sect. 26.11 considered in RWIND Simulation?

New FAQ 004301 EN

In the ASCE 7-16, the conservative value for the Gust-factor, G, is 0.85 for rigid buildings. The engineer can calculate an alternative and more accurate value. The Gust-effect, Gf, for flexible buildings accounts for size and gust size similar to rigid buildings but also considers dynamic amplification including wind speed, natural frequency, and damping ratio.

The Gust-factor G or Gf, is considered to be 1.0 in RWIND Simulation. The structure is rigidly simulated in the numerical wind tunnel. The loads which are transferred back into RFEM are applied to the elastic structure with true stiffness considered.

To account for any value other than 1.0 for this factor, the wind load case factor can be adjusted in RFEM under the applicable load combination.
• According to DIN EN 1995-1-1/NA, the crack factor kcr may be increased by 30% for softwood in areas at least 1.50 m from the end of the timber grain. How to implement it in RF-/TIMBER Pro?

New FAQ 004298 EN

The increase of the crack factor kcr still has to be done manually because the program does not know where the end of the grain is defined. To do this, divide the member by 1.5 m from the end of the grain so that the affected areas can be designed as a separate member (see Figure 01).

Two design cases are now required (File → New Case ...). In case 1, members within the 1.5 m are selected for the design. In case 2, it is necessary to select the members where the 30% needs to be considered. Then, in case 2, the kcr value is adjusted manually in the settings for the National Annex. Thus, a kcr of 0.65 results for C24, which is entered as shown in Figure 02. The design is carried out this way with an increased kcr value.
• How to control an overpressed joint in the ridge?

FAQ 004286 EN

An overpressed joint between two members can be controlled in RFEM by means of the member stress results. For members, this stress result represents the effective stress as a color gradient across the member surface depending on the assigned cross-section.

Figure 01 - Stresses on Members

Based on the local member axis, the member stress result gives the following stress components and reference stresses with an associated color palette:

• Stress
• σx
• τy
• τz
• Elastic stress component
• σN
• σMy
• σMz
• σN+My
• σN+Mz
• σM
• Elastic equivalent stresses
• σv,Mises
• σv,Tresce
• σv,Rankine
• σv,Tresca+Rankine
• σv,Bach

Using active displaying for the members connected to the joint, and displaying the σx stresses, it is possible to visualize the state of stress on and thus also between the members. If only negative stresses occur in the area between the members, the joint is overpressed.

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

FAQ 004281 EN

The shear correction factor is taken into account in the RF-LAMINATE program 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 the shear stiffness itself can be found on page 15 of the English version to the manual of RF-LAMINATE as follows:

For the 10 cm thick plate in Figure 1, the calculation of the shear correction factor is shown. The equations used here are only valid for the simplified symmetrical plate structures!

 Layer z_min z_max E_x (z) (N/mm²) G_xz (z) (N/mm²) 1 -50 -30 11000 690 2 -30 -10 300 50 3 -10 10 11000 690 4 10 30 300 50 5 30 50 11000 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$}_{i,min}^3}3$

$=11000\left(\frac{-30^3}3+\frac{50^3}3\right)+300\left(\frac{-10^3}3+\frac{30^3}3\right)$

$+11000\left(\frac{10^3}3+\frac{10^3}3\right)+300\left(\frac{30^3}3-\frac{10^3}3\right)+11000\left(\frac{50^3}3-\frac{30^3}3\right)$

$=731,2\times10^6Nmm$

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

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

 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

$k_z=\frac{43,4}{{(731,2e^6)}^2}6,713284\;e^{13}=5,449\;e^{-3}$

$D_{44}=\frac{{\displaystyle\sum_i}G_{xz,i}A_i}{k_z}=\frac{43,4}{5,449\;e^{-3}}=7964,7N/mm$

This corresponds to the value output in RF-LAMINATE (Figure 2).
• Despite having defined average regions, they are not taken into account for the design in RF-LAMINATE Surfaces. Which setting did I miss here?

FAQ 004275 EN

To consider average regions when designing in RF-LAMINATE, they must always be activated in the detail settings of the add-on module. See Figure 01 with the detailed settings in RF-LAMINATE for this.

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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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