Frequently Asked Questions (FAQ)

Search FAQ

Show Filter Hide Filter





Customer Support 24/7

Knowledge Base

In addition to our technical support (e.g. via chat), you’ll find resources on our website that may help you with your design using Dlubal Software.

Newsletter

Receive information including news, useful tips, scheduled events, special offers, and vouchers on a regular basis.

1 - 10 of 137

Sort by:

  • Answer

    In most cases, a resulting shear force or a shear force applied over the height is of interest, and not the actual surface distribution. For this, there are two tools for displaying the forces. This is shown in the following example of a shear force. Furthermore, the procedure is shown in the video.

    Evaluation by Section
    By using a section, the distribution can be displayed graphically as a result diagram. In order to read out the shear force for the example shown in Figure 01, the shear flow nxy is required. This result diagram can then be further evaluated in the result diagram, for example, to determine the resulting shear force. Furthermore, the resultant can also be displayed graphically. In order to neglect the influence of supports, it is not recommended to create the section directly on the ground line of the surface. Basically, the following applies: The finer is the FE mesh, the more accurate are the results.

    Evaluation by Result Beam
    Another option is to use a result beam that integrates the surface internal forces and displays them as member internal forces. If you are only interested in the internal forces, you can select any cross-section because the result beam does not bring any further stiffness into the structural system. The advantage of the result beam is that the assigned cross-section can also be designed in the add-on modules.
  • Answer

    For modeling the columns, bottom ribs, top ribs, and so on, you can use members for timber panels covered on one side.

    If the timber panel is covered on both sides, it is recommended to replace the members with surfaces. The columns are hinged to the top and the bottom rib. Then, you can define the covering.

    For timber surfaces, make sure that the orthotropic material model is used.

    When defining supports, you can decide whether they should be linear or nonlinear.

    The flexibility of the connection between the covering and the members can be set by using line releases. The springs refer to a length of 1 meter (kN/m/m = kN/m²), which is why the displacement modulus of the fastener must be multiplied by the number of fasteners per linear meter.

    In the video, you can see the exact procedure. It shows the results first, and then the modeling.

  • Answer

    The definition of the forces is specified in the corresponding dialog box (see Figure 01). The maximum friction force depends on the load in the Y‑direction or Z‑direction. Depending on which interaction formula is used, there are different friction forces as a result.

    Example

    A support should transfer the force in the global X-direction by friction. The friction coefficient is 0.1 for all directions. The support force PY is 5 kN and the support force PZ is 10 kN.

    This results in the following maximum support force in the X-direction for the "Friction PY' PZ' ..." nonlinearity:

    ${\mathrm P}_{\mathrm X,\max}\;=\;{\mathrm\mu}_{\mathrm X}\;\cdot\;\sqrt{\;{\mathrm P}_{\mathrm Y}^2\;+\;{\mathrm P}_{\mathrm Z}^2}\\{\mathrm P}_{\mathrm X,\max}\;=\;0.1\;\cdot\;\sqrt{\;5^2\;+\;10^2}\;=\;1.118\;\mathrm{kN}$

    For the second option "Friction PY'+ PZ'...," the maximum support force results in:

    ${\mathrm P}_{\mathrm X,\max}\;=\;{\mathrm\mu}_{\mathrm{XY}}\;\cdot\;\left|{\mathrm P}_{\mathrm Y}\right|\;+\;{\mathrm\mu}_{\mathrm{XZ}}\;\cdot\;\left|{\mathrm P}_{\mathrm Z}\right|\\{\mathrm P}_{\mathrm X,\max}\;=\;0.1\;\cdot\;5\;+\;0.1\;\cdot\;10\;=\;1.500\;\mathrm{kN}$

    While the resulting support force is used to determine the friction force in the first option, the forces are added linearly in the second option.

    Thus, the structural system shown in Figure 02 becomes unstable as of the force > 1.118 kN for the first option, and as of the force > 1.500 kN for the second option.

  • Answer

    A glTF file contains a 3D model that is saved in the GL Transmission Format (glTF) format. This 3D model can be viewed in any glTF viewer. B. can be integrated into your own web pages using JavaScript. An example of this is shown here:


    This 3D model is now saved with the RFEM and RSTAB file by default, or can be exported separately (see Figure 01). You can find more examples on our homepage under Downloads → Models for Download (see link below this FAQ). You can rotate the model by holding down the mouse button or zoom it using the mouse wheel.

  • Answer

    The sign convention depends on the orientation of the local z-axis. In General Data, you can define the orientation of it (see Figure 01).

    If the global Z-axis is oriented downwards, the local z-axis is automatically oriented downwards. It is not possible to orient them upwards. If the global z-axis is still oriented upwards, you have the option to determine the orientation of the local z‑axis upwards or downwards.

    If the orientation of the local z-axis is set to downwards in General Data, the following applies:
    • The bending moment My is positive if tensile stresses occur at the positive member face (in the direction of the z axis). Mz is positive if compressive stresses occur at the positive member face (in the direction of the y axis). The sign definition for torsional moments, axial forces, and shear forces conforms to the usual conventions: These internal forces are positive if they act on the positive section in a positive direction.
    If the orientation of the local z-axis is set to upwards in General Data, the following applies:
    • The bending moment My is positive if compressive stresses occur at the positive member face (in the direction of the z axis). Mz is positive if tensile stresses occur at the positive member face (in the direction of the y axis). The sign definition for torsional moments and axial forces conforms to the usual conventions. These internal forces are positive if they act on the positive section in a positive direction. The shear forces are positive if they act in the negative direction on the positive face.
  • Answer

    Yes, it is possible - but only in RFEM . Unfortunately, this function does not exist in RSTAB.

    To use the export of stiffnesses, it is necessary to activate the options shown in Figure 01 in Details. Thus, the stiffnesses are exported to RFEM before the calculation and the internal forces are calculated taking into account the flexible connections. However, no further static model is created, but the existing model is modified.

    When you start the RF-JOINTS calculation, the eccentricity and connection are transferred to RFEM as member properties, and nodal releases are also generated in RFEM. This information can be found in the RFEM tables "1.14 Member Hinges", "1.15 Member Eccentricities", "1.24 Nodal Releases" and "1.30 Connections". The internal forces for the designs are then determined with the modified model.

    There are export options for all members you can define eccentricities and hinges for. If there are already members with hinges or if there are trusses in the model, the additional connection hinges would lead to instabilities in the calculation. Therefore, a corresponding message appears before the dialog box is closed.

    In the downloads at the end of this FAQ, you can find an example where the stiffness export is only shown for the eaves node. If you want to consider the flexibility of the fasteners, you should define all connections.

  • Answer

    In order to perform a smooth calculation, the program defines a maximum number of connected members as well as a minimum angle between members. The geometric conditions are defined as follows:

    • Maximum number of connected members: 8
    • Minimum length of a member: 42 cm
    • Minimum angle between members: 15°

    If these boundary conditions are not met, a further calculation is not possible.

  • Answer

    First, you should consider whether it is not easier for the different combination rule to define the load combinations manually in addition to the automatically generated combinations: If there are only a few load combinations, they can be created quickly. However, if the effort is too great due to many load cases, you can proceed as follows:

    Example

    For the combination rule "earthquake" according to EN 1990, the snow (≤ 1000 m) should be considered with 0.5 instead of ψ2 = 0.0. For the "Permanent/Temporary" design situation, however, soll2 should be considered as 0.0 according to the standard.

    In order to consider different values for the two combination rules, it is necessary to copy the snow load case and to change the action category of the copied load case to "Other" (see Figure 01).

    Figure 01 - Copying Load Case and Assigning Action Category

    By default, the combination factor ψ2 is stored with 0.5 for this action category (see Figure 02).

    Figure 02 - Combination Coefficients

    If you need a different value, you can select a different, suitable action combination for the copied load case. If there is no action category that meets the desired value, you can create a user-defined standard. You can find the description of how to do it under the link below this FAQ.

    In order to avoid the superposition of Load Case 3 and Load Case 4 shown in Figure 01, the respective load case must be excluded in the combination expressions. To do this, use the "Reduce number of load cases ..." function (see Figure 03).

    Figure 03 - reducing number of load cases

    Then, you can assign the load cases to be combined with the respective combination expressions (see Figure 04 and Figure 05).

    Figure 04 - Settings for Permanent/Temporary Design Situation

    Figure 05 - Setting for the seismic design situation

    You now receive the desired load combinations (see Figure 06).

    Figure 06 - Completely Generated Load Combinations

  • Answer

    A loose ridge wedge can be considered for beam types 5 and 6, that is, only for the types of pitched cambered beams. This option is not available for Beam Type 3 of double tapered beam.
  • Answer

    This information is available in the Results navigator for members (see Figure 01). The member lengths are displayed with regard to the stressed structural system and the unstressed system. The "stressed length" is obtained from the form-finding under consideration of prestresses.

    The recalculation to the "stressed length" can be done manually using Hooke's law:

    ${\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\mathrm{Δl}\\\\\mathrm\sigma\;=\;\mathrm E\;\cdot\;\mathrm\varepsilon\\\frac{\mathrm F}{\mathrm A}\;=\;\mathrm E\;\cdot\;\frac{\mathrm{Δl}}{\mathrm l}\\\mathrm{Δl}\;=\;\frac{\mathrm F\;\cdot\;\mathrm l}{\mathrm E\;\cdot\;\mathrm A}\\\\{\mathrm l}_{\mathrm{unstressed}}\;=\;{\mathrm l}_{\mathrm{stressed}}\;-\;\frac{\mathrm F\;\cdot\;{\mathrm l}_{\mathrm{stressed}}}{\mathrm E\;\cdot\;\mathrm A}\;=\;{\mathrm l}_{\mathrm{stressed}}\;\cdot\;\left(1-\;\frac{\mathrm F\;}{\mathrm E\;\cdot\;\mathrm A}\right)$

1 - 10 of 137

Contact us

Did you find your question?
If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

+49 9673 9203 0

info@dlubal.com

First Steps

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.

Your support is by far the best

“Thank you for the valuable information.

I would like to pay a compliment to your support team. I am always impressed how quickly and professionally the questions are answered. I have used a lot of software with a support contract in the field of structural analysis, but your support is by far the best. ”