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Frequently Asked Questions (FAQ)
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AnswerThe calculation of the results in grid points is important for displaying values on surfaces, among other things. You can find the information about grid points here.The problem is that in the case of complex structures and many load combinations, the calculation in grid points is relatively time-consuming and therefore, it requires a large amount of memory. Even if you perform the calculation in FE nodes as shown in Figure 01, it is always necessary to additionally perform the calculation in grid points. Otherwise, the results cannot be displayed in grid points under Values on Surfaces.For complex structures, it is recommended to deactivate this option to perform a faster calculation.
It is possible to use the "isolines" instead of displaying the results with "isobands" in the graphic.
First, switch to the "Isolines" display.
Then, you can additionally set in the Display navigator that the "Result Values Defined Automatically" should be displayed for the isolines.
AnswerSuch a feature for increasing the load up to the failure does not exist with regard to the design of reinforced concrete structures.As an alternative, you can proceed as follows:Create a separate load case or load combination for each load increment. This can be done by using load factors, for example.Then, select the individual load cases or combinations in the add-on module.After performing the calculation to the point "Provided Reinforcement" for the first time, you can adjust and save the existing reinforcement proposed by the add-on module.Finally, you can carry out the nonlinear analysis on the basis of the defined reinforcement.The existing safety or the available utilization can be evaluated graphically after the successful calculation.
AnswerFor the design on a 3D model, you should pay attention to normal forces. The normal force can affect the loading of the respective direction, but can also affect the minimum lever arm.In RF‑CONCRETE Surfaces, the smaller lever arm from both reinforcement directions is applied in 3D structures. In this context, the normal force in Direction 1 can have an impact on the required reinforcement in Direction 2.
AnswerIn RF‑IMP, you have selected the "Generate pre-deformed FE mesh" option. In this case, the imperfect structure is considered in the calculation by using the deformed FE mesh generated in RF‑IMP. Thus, the CO results refer to the coordinates of the pre-deformed FE mesh and not to the original position in the perfect system.To better explain this issue, I exported the coordinates of the pre-deformed FE mesh nodes from RF‑IMP to Excel. Based on this information, an imperfect structure was created in a new RFEM file and calculated according to the second-order analysis. The left window shows the deformation of the perfect structure considering RF‑STABILITY and RF‑IMP, and the right window shows the result of the imperfect structure. The results are identical.
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.
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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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