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Frequently Asked Questions (FAQ)
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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.
The RF‑CONCRETE NL add-on module is a module extension of RF‑CONCRETE Surfaces.
The calculation of deformations in cracked sections (state II) with RF‑CONCRETE NL can be activated by setting the "Nonlinear" method of check in the "Serviceability Limit State" tab of RF‑CONCRETE Surfaces.
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.
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.
The selection in the "Limit of Crack Widths" tab of Window "1.3 Surfaces" has a direct impact on the kc factor for the analytical calculation of the minimum reinforcement As,min for effects due to restraint according to Equation (7.1) of DIN EN 1992‑1‑1, 7.3.2.If selecting the "pure tension restraint," the value kc = 1.0 applies in Equation (7.1). In the case of the approach of "bending Restraint," the add-on module sets the kc factor strictly to 0.4.If you select "Depending on the defined load," the program interpolates the element of the kc value by the element depending on the stress distribution in the cross-section using the defined load.This results in a constant distribution of the minimum reinforcement due to restraint being determined for the respective reinforcement direction of the surface when selecting "pure tension restraint" or "bending restraint." If you select "Depending on the defined load," there will be no constant distribution of the minimum reinforcement due to restraint.The program behavior described above is the same in RF‑CONCRETE Members and RF‑CONCRETE Surfaces (in RFEM 5), and is also applied to the CONCRETE add-on module (in RSTAB 8).
AnswerYes, it is possible to select the high-strength steel SAS 670 for nonlinear design in RF‑CONCRETE Members. In this way, you can perform stability analysis for columns, among other things.The steel can be selected in the Materials section of the add-on module (see Figure 01). Since DIN EN 1992‑1‑1 only allows fyk = 500 N/mm² by default, this limit must be adjusted when using SAS 670.In General Data, you can create a user-defined National Annex where the maximum value of yield strength is increased to fyk ≥ 670 N/mm² in Point 3.2 (see Figure 02).
AnswerNo, this is unfortunately not possible.The intermediate values from the calculation (for example, effective depth d applied for shear force design) are only available for the selected FE node or grid point when opening the "Design Details" dialog box. But not for all FE mesh nodes of the designed surfaces.Therefore, these intermediate values cannot be used for a graphic display on the model, but only in tables under the design details.
AnswerIn this case, the Calculation Method and the type of the 2D model are important.When using the analytical method (RF‑CONCRETE Deflect), it is possible to perform the calculation in 2D models. When using the nonlinear method (RF‑CONCRETE NL), the calculation for 2D XY (uZ/φX/φY) is not possible. In the nonlinear calculation, shrinkage is represented internally as strain load, which is not possible in this type of 2D model due to the limited degrees of freedom.Convert 2D to 3D ModelIn General Data, you can simply convert a 2D model into a 3D model. For the supports, all degrees of freedom not contained in the 2D model are fixed when converting to a 3D model (see the video).
Yes, you can, because the nonlinear reinforced concrete design is also included in the CONCRETE add-on module for RSTAB 8. Thus, you can activate "Nonlinear calculation" in the "Ultimate Limit State" tab.
In the detail settings for the nonlinear calculation, you can select "General design method for members in axial compression acc. to second order theory."
In this case, it is important to define the imperfections in RSTAB and apply load combinations (CO) according to the second-order analysis, no result combinations (RC), for the design!
Note to RFEM 5:
In RFEM 5, the same procedure is possible in RF‑CONCRETE Members. However, RFEM requires the RF‑CONCRETE NL add-on module for the nonlinear reinforced concrete design.
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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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