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

New 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).
• ### How does the RF-GLASS determine bond stress?

FAQ 004232 EN

In RF-GLAS, there are two different types of calculations. On the one hand, the so-called '2D' calculation. In this case, the glass structure is represented as a surface element. When considering the shear bond, an equivalent cross-section is determined using the laminate theory In contrast to this, there is the '3D' calculation. In this case, the layer structure is represented as a solid element in the calculation and thus the effectiveness of the stiffnesses between foil and glass is exactly determined when the shear bond is taken into account.

The RF-GLAS manual, Chapter 2, also provides further information on method of analysis.

• ### "During the calculation of material non-linearity, the material with a decreasing branch of the diagram can be calculated with one load increment only." Why do I get this error?

FAQ 004188 EN

Only the default setting of 1 load increment can be set when a complex nonlinear material model is defined. The reason for this is because the program cannot determine the correct material stiffness for each incremental loading amount. The exact maximum load needs to be applied to the structure in order to determine the state of the material's stress/strain diagram.

Figure 01 - Material Model - Nonlinear material defined

This setting can be found and changed under "Calculation Parameters" as well as under the "Calculation Parameters" in the load cases and combinations dialog box.

• ### How to set the calculation parameters using the COM interface?

FAQ 004184 EN

The following code shows how to get different calculation parameters via the COM interface. It also demonstrates how to specify a setting for deactivating shear stiffness:

    '   get model interface    Set iApp = iModel.GetApplication()    iApp.LockLicense        '   get calculation interface    Dim iCalc As RFEM5.ICalculation2    Set iCalc = iModel.GetCalculation        '   get surface bending theory    Dim calc_bend As RFEM5.BendingTheoryType    calc_bend = iCalc.GetBendingTheory        '   get settings for nonlinearities    Dim calc_nl As RFEM5.CalculationNonlinearities    calc_nl = iCalc.GetNonlinearities        '   get precision and tolerance settings    Dim calc_prec As RFEM5.PrecisionAndTolerance    calc_prec = iCalc.GetPrecisionAndTolerance        '   get calculation settings    Dim calc_sets As RFEM5.CalculationSettings    calc_sets = iCalc.GetSettings    'get calculate options    Dim calc_opts As RFEM5.CalculationOptions    calc_opts = iCalc.GetOptions        '   set ShearStiffness to false    calc_opts.ShearStiffness = False    iCalc.SetOptions calc_opts
• ### Is it possible to perform stability analyses on reinforced concrete structures by means of RF-STABILITY?

New FAQ 004164 EN

Since concrete has a nonlinear material behavior that can only be simulated with the CONCRETE NL module, it is not possible to analyze it with the RF-STABILITY add-on module.

The use of another material model such as isotropic linear elastic or isotropic plastic would not represent the crack formation correctly and the results are therefore not usable.

A stability analysis on columns can be performed with RF-CONCRETE Columns or RF-CONCRETE NL. You can find a small example in Downloads.

This example includes the design of a column by the RF-CONCRETE Columns add-on module. Make sure that the calculation of the internal forces in RFEM is performed according to the first-order analysis and that no imperfections are required because the method used in the module takes them into account.

The example also includes the design with RF-CONCRETE NL. Here again, it is necessary to calculate according to the second-order analysis and imperfections in the form of inclinations are required. For better comparability, the layout of the longitudinal reinforcement was aligned with the result from RF-CONCRETE Columns, as shown in Figures 01 and 02. Since the reinforcement is optimized by the module after a new calculation, the wanted reinforcement was saved as a template (see red arrow).

• ### Which equation solving method should I use, direct and iterative?

FAQ 003626 EN

The choice of the solver method leading quickly to results depends on the complexity of the model and the main memory (RAM) that is available:

• For small and medium sized systems, the direct method is more effective.
• For very large structures, the iterative method leads to results more quickly.
As soon as the matrices for the direct method cannot be stored any longer in the main memory, Windows starts to swap out parts of the data to the hard disk. The hard disk activities will increase and the processor load will be reduced which is visible in the Windows Task Manager. This memory problem can be avoided by switching to the iterative ICG (Incomplete Conjugate Gradient) calculation method.

• ### How does the asynchronous calculation via the COM interface work?

FAQ 003605 EN

The asynchronous calculation is used if a self-created program should only open or continue RFEM or RSTAB. When the calculation is complete, the event is transferred via a delegate. You can find a C# example in a Visual Studio project in the download area below.
• ### During the calculation, I receive an error message in RFEM with the Error No. 1639 or in RSTAB with the Error No. 1640 'Member No. XY | Member end hinges No. YZ are freely rotating about the x-axis. Please check this in Table 1.17 (or 1.7 in RSTAB) or in a related table'. How to solve this problem?

FAQ 003596 EN

In fact, this error message appears only if a member end hinge that allows a rotation about the local x-axis has been assigned to a member at both ends. Thus, the member can rotate freely about its own axis and is therefore unstable.

Assign a new release to one of the member ends where the degree of freedom φx is not hinged.
• ### For the deformation analysis by means of RF-CONCRETE Deflect, I have activated the consideration of creep and shrinkage. Where can I see the creep coefficient and shrinkage strain applied for the calculation?

FAQ 003581 EN

In Table 1.3 Surfaces, you can specify the parameters in the corresponding tab for the automatic determination of the creep coefficient and shrinkage strain. It is also possible to enter user-defined values there, if necessary.
• ### Which calculation methods are used by RSTAB and RSBUCK?

FAQ 003564 EN

RSTAB is a FEM program that uses trigonometric trial functions for the members. For this reason, members do not have to be subdivided for sufficiently accurate results and the calculation speed is correspondingly higher.

RSBUCK determines the eigenvalues of the stiffness matrix and can thus linearly calculate the critical load and buckling mode of the structure.

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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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