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Frequently Asked Questions (FAQ)
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First, the ribbed plate should not be modeled with the classic rib member from RFEM, but with an eccentric beam member that is arranged on the bottom surface of the actual plate. Rib members cannot be calculated with RF-CONCRETE NL with regard to deformations.
The eccentric beam is then designed in RF‑CONCRETE Members. In the "Serviceability Limit State" tab of Window 1.1, you can activate the "Nonlinear calculation.". In the detailed settings for the nonlinear calculation, you can activate the export of stiffness from the nonlinear calculation.
In the example presented here, the stiffness is exported "individually" for each LC calculated in RF‑CONCRETE Members. You can find more information about the options "Individual" and "Consistent for reference load" under the link below.
After the calculation in RF‑CONCRETE Members, the exported stiffnesses of the calculated COs are available in RFEM, where you can activate them in the respective COs for a new calculation of internal forces. To do this, activate the extra options of the respective CO. In the "Extra Options" tab, you can then activate the stiffness exported from the RF‑CONCRETE Members add-on module for a new determination of internal forces.
After recalculating the internal forces of the COs in RFEM (taking into account the exported stiffness from RF‑CONCRETE Members), you can apply them for design in RF‑CONCRETE Surfaces.
The following figure shows the deformations of the ribbed plate in RF‑CONCRETE Surfaces, taking into account the stiffness in cracked state from the design in RF‑CONCRETE Members.
In comparison to Figure 03, the linear-elastic stiffness in uncracked state (state I) was applied in Figure 04 for the eccentric beam.
Notes on the procedure described above:
- In this case, the calculation was performed in RF‑CONCRETE Members first, and the resulting stiffness was exported. This approach was selected because it was assumed that the eccentric rectangular cross-section will proceed to the cracked state (state II) first.
- The procedure shown "only" describes one iteration and is therefore only an "approximation" since an uncracked plate was assumed for the calculation of the eccentric rectangular cross-section.
- The shrinkage effect is applied as an external load in the NL calculation in RF‑CONCRETE Members. This means that, for example, an unsymmetric reinforcement would result in an additional curvature, even if the cross-section remained in the uncracked state. When calculating the plate in RF‑CONCRETE Surfaces, this effect of shrinkage on the member cross-section is not taken into account anymore.
AnswerThe axis orientation of the surfaces in your model is probably not adjusted. For a circular surface, it is recommended to specify the orientation of the axes for surfaces or the axes for results of the surfaces.You can adjust the axes for each surface. In the "Axes" tab, you can find the subtabs "Axes for Input" and "Axes for Results."The "Axes for Results" tab adjusts the axes of the surface for the results. Here you can specify the orientation of the axes using a point, for example. A great advantage of this method is that the results are not deleted when adjusting the axes.The "Axes for Input" tab adjusts the axes of the surface for the orientation and results. Here you can specify the orientation of the axes on a line, for example.The results of both axis adjustments are the same. For symmetric loading, the expected symmetric results are provided.
In RF‑CONCRETE Surfaces, the compression reinforcement is calculated as well.
The note "compression reinforcement" is displayed in the design details for the respective reinforcement layer.
Yes, it does make a difference whether the surface is divided or not.
If the line with the line hinge arranged on it is only integrated into the surface and the surface is not divided, the RFEM solver uses a different calculation method than for a surface divided into partial surfaces.
For a line that is only integrated into a surface, the stiffness of the first element row is reduced in order to approximate the line hinge.
When applying partial surfaces, the line hinge is implemented internally by means of line releases so that the hinge can be modeled more precisely.
Furthermore, it is also necessary to check the FE mesh in this comparison. Depending on the geometry of the surfaces and the set FE mesh size, the FE mesh can deviate significantly, so there may be result deviations in addition to the different calculation methods. In this case, the FE mesh can be approximated by FE mesh refinements, if necessary.
The "Cable on Pulleys" member type can only describe the forces N and displacements u‑x in the direction of the cable. Therefore, it cannot be combined with regard to the form‑finding, for example, at the edge of membrane surfaces.
For this, see also Chapter 4.17 in the online manual for RFEM 5.
AnswerThe RF-STEEL AISC module does not optimize cross-sections for the Serviceability Limit State design. Optimization is only calculated for the Ultimate Limit State design.Users must manually adjust the cross-section in RFEM or within the add-on module and can export the cross-section back into RFEM. In either scenario, the model must be rerun in order to calculate the correct internal forces with adjusted member size.
RWIND Simulation is exclusively compatible with RFEM due to the CFD modeling, which requires a finite element calculation. The model created in RSTAB can be opened in RFEM. The wind load parameters can be defined in the Simulate and Generate Wind Loads dialog box of RFEM.
At the bottom of the Wind load tab, it is possible to remain and automatically generate loads for the corresponding load cases the CFD calculation has been performed in the background.
If you would rather perform the wind simulation in RWIND, click the Open in RWIND Simulation button in the Load Cases tab.
To obtain the trial version of RWIND Simulation, proceed as described in this FAQ.
AnswerIf the distorted elements are so small that they cannot be detected (see Figure 01), it is recommended to "Display Mesh Quality Annotations." You can find this option in the Display navigator → FE Mesh → FE Mesh Quality. There, you can activate the annotations for the "Warning" and "Failure" elements (see Figure 02). Thus, you can immediately recognize where the location is by using the values. For larger models, it may be helpful to hide the model during the search.
A solid must always be completely closed. To clarify the problem, imagine filling the solid with a liquid. The liquid must not escape from the solid at any point.
The attached video shows how to easily and effeciently insert the missing surfaces.
AnswerThe nonlinear material models are only available in the 3D environment. Please make sure that the model type is set to "3D" (see Figure 02).
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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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