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  • 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).
  • 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:

  • Answer

    The easiest way to consider this is to use the RF-/JOINTS Timber Steel to Timber module. For this purpose, the module decomposes the original connection, and creates a new structural system that considers the flexibility accordingly. This is taken into account separately for load-bearing capacity, suitability for use, and exceptional.
  • Answer

    In RFEM and RSTAB, the simplified design 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.

  • Answer

    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.
  • 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!

    Layerz_minz_maxE_x(z)(N/mm²)G_xz(z)(N/mm²)
    1-50-3011,000690
    2-30-1030050
    3-101011,000690
    4103030050
    5305011,000690

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

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

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

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

    $=731.2\times10^6 Nmm$

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

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


    χ113.75 106
    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).
  • Answer

    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.
  • Answer

    Basically, all cross-sections of the solid and hybrid cross-section groups can be designed in the RF-/TIMBER Pro program. In Figure 01, they are displayed on the right.

    For more complex asymmetrical cross-section shapes, it may be necessary to adjust the allowable inclination of principal axis on a user-defined basis in the add-on module (see Figure 02).

  • Answer

    In the case of cross laminated timber panels not glued to the narrow sides and a wall-like structural behaviour, the torsion stress in the glued joints is often decisive. This design is performed according to the explanations in the literature reference below according to the following equation.

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

    Values:
    • b board width
    • n number of board layers
    • nxy shear in pane plane
    • $\frac{\partial n_x}{\partial x}$ shear of board layers
    • $\tau_{xz}$ shear in thickness direction
    • fR rolling shear strength
    • fv,tor torsional shear strength
    For the y-direction, the design is analogous but with the values for the y-direction.
  • 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.

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