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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.
In the design modules of RFEM or RSTAB, you can define "Provided Basic Reinforcement" and perform a nonlinear calculation in the ultimate limit state for this reinforcement.
As a result, you obtain the utilization ratio from the nonlinear calculation assuming the provided longitudinal reinforcement.
The nonlinear calculation is already included in the CONCRETE add-on module for RSTAB. In RFEM, the RF‑CONCRETE NL add-on module is required.
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.
AnswerThe partial safety factors for reinforced concrete design can be edited in Window 1.6 "Reinforcement" in the corresponding tab for the selected National Annex (for example, DIN EN 1992‑1‑1).If required, you can also reset these values to the default value.In a similar way, this also applies to the add-on modules RF‑CONCRETE Surfaces and RF‑/CONCRETE Columns.
The RF‑CONCRETE Columns add-on module allows you to define a "creep-producing permanent load." You can find the corresponding tab in Window "1.1 General Data."
The reason for the entry is that RF‑CONCRETE Columns can apply this "creep-producing permanent load" for the automatic determination of the effective creep ratio according to EN 1992‑1‑1, 5.8.4.
In contrast, there is no explicit input option for this creep-producing permanent load in RF‑CONCRETE Members. In RF‑CONCRETE Members, the stability analysis of reinforced concrete columns by means of nonlinear design does not automatically reduce the effective creep ratio. You can find the background to the effective creep ratio applied in RF‑CONCRETE Members in Chapter 2.4.6 of the RF-CONCRETE Members manual.
The same applies to the CONCRETE Columns or CONCRETE add-on modules for RSTAB.
In the case of cross-section design, RF‑CONCRETE Members or CONCRETE uses in the calculation the stress-strain diagram for reinforcing steel according to DIN EN 1992‑1‑1, 3.2.7(2)a, that is, the increasing upper part up to ftk and the strain limitation of εud = 0.025.
In RF‑CONCRETE Members or CONCRETE, there is no option to switch to the design with the horizontal part according to 3.2.7(2)b.
However, you can possibly use a user-defined material with ftk = fyk.
After the calculation, you can switch to the result window "2.4 Required Reinforcement by x‑Location" in the RF‑CONCRETE Members (RFEM) or CONCRETE (RSTAB) add-on module.
Here, you can select a certain result row for a particular design and x-location (upper table in Window 2.4). Then, you can evaluate the intermediate results in the lower table in Window 2.4. This covers the "Neutral Axis Depth x", for example. The location of the neutral axis for the selected design location is displayed in the graphic on the right of Window 2.4 .
Furthermore, you can display the distribution of the neutral axis depth along the member length graphically in the model or in "Result Diagrams on Member."
You can find the setting in Window 1.5 Support.
Here, you can enter the support width and type, and specify whether to carry out the moment redistribution, or the reduction of moments or shear forces.
Depending on the standard selected in Window 1.1, there are different options available. The option applies to RF‑CONCRETE Members (RFEM 5) and CONCRETE (RSTAB 8).
Yes, it does, because this affects the stiffness of the entire structure.
When entering a flush beam as a "Rib," you will add the stiffness of the defined rectangular cross-section to the area of the line.
However, you have to only define the integration width for the result beam. The entered rectangular cross-section does not affect the stiffness of the entire structure, but is only applied as a design cross-section in the add-on modules (for example, RF‑CONCRETE Members).
AnswerA non-designable situation like this is displayed if the shear resistance without shear reinforcement VRd,c is arithmetically smaller than zero.The value for VRd,c of less than zero is caused by large tensile axial forces. In this context, the cross-section is completely under tension or completely cracked, and no shear force resistance can be created.For coated cross-sections with planned shear reinforcement, the following situation results:If VRd,c < 0, no further shear design is performed in RF‑CONCRETE Surfaces, and Note 13) is displayed. This approach is conservative.In this context, there was a request (194) for the interpretation of the standard, which allows the truss model to be used even with a completely cracked cross-section.If a shear reinforcement is designed as planned, you can ignore the message about the non-designable situation in the program. In this case, you should ensure that VEd is smaller than VRd,max and VRd,s.
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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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