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Frequently Asked Questions (FAQ)
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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.
RF-CONCRETE Columns determines the equivalent moment M0e from the moment M02 at the column head and M01 at the column base according to EN 1992‑1‑1, 18.104.22.168 (2), and performs the design according to the model column method with this equivalent moment M0e.
Now, it may happen, for example, that a computationally larger required reinforcement area would result from the cross-section design with the moment M01 at the column head.
To ensure this, message 28) is displayed, according to which the user should perform a standard design with the internal forces according to the linear static analysis. To do this, simply open the RF‑CONCRETE Members add-on module and perform pure design of the internal forces according to the linear static analysis for the member designed in RF‑CONCRETE Columns.
AnswerFor the punching shear design on a column, RF-PUNCH Pro requires a node at which the axial force of the column can be tapped for the design.If you have displayed the column as a solid (for example, with a rectangular cross-section) and directly connect this solid to the floor, you cannot use this situation for the design in RF-PUNCH Pro. The member internal force is missing because only one solid is used.However, you can provide the end of the solid with a short coupling member (for example, a rigid member). Then, the rigid member can be connected to the floor at an end node, and the axial force in the coupling member can be used for the punching shear design.Please note that the dimensions of the coupling member or rigid member need not be defined in the RFEM model. Therefore, the RF-PUNCH Pro applies standard dimensions for the column cross-section.
AnswerYes, for the nonlinear calculation in RF-CONCRETE Members, it is possible to select the high-strength steel SAS 670 for the design. In this way, you can perform stability analysis for columns, among other things.The steel can be selected in the Materials section of the 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 the 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).
AnswerBoth RFEM and RSTAB provide a suitable solution. In addition to Eurocode 2, the international standards, such as ACI 318, CSA A23.3, SIA 262, or GB 50010, are also available for the design in both programs.
With the add-on modules for designing columns or foundations, or for punching shear designs, it is possible to quickly and reliably calculate the structural components.
Main Programs RFEM or RSTABThe main programs RFEM or RSTAB are used to define structures, materials, and actions.
For reinforced concrete structures, RFEM is clearly the first choice as it allows you to also create structural systems consisting of plates, walls and shells in addition to spatial frame structures. RFEM is the more diverse variant as it can be equipped and extended with the corresponding add-on modules for all materials and designs.
- Eurocode 2 (EN 1992-1-1)
- SIA 262
- ACI 318
- CSA A23.3
- GB 50010
- RF-/CONCRETE Columns
Reinforced concrete design according to the model column method or the nominal curvature method
- RF-PUNCH Pro
Punching shear designs of surfaces
- RF-/FOUNDATION Pro
Design of single, bucket and block foundations
- RF-CONCRETE Deflect (RFEM)
Analytical deformation analysis
- RF-CONCRETE NL
Realistic deformation analysis of surfaces and members
Dynamic AnalysisIf it is necessary to perform seismic analysis or vibration designs of a building, the RF‑/DYNAM Pro add-on modules provide special tools for determining natural frequencies and mode shapes, for an analysis of forced vibrations, a generation of equivalent loads, or for a nonlinear time history analysis.If you have any question about the Dlubal Software programs, please do not hesitate to contact the sales department.
Since concrete has a nonlinear material behavior that can only be simulated with the CONCRETE NL module, it is not possible to analyze it by using the RF‑STABILITY add-on module.
The use of another material model such as isotropic linear elastic or isotropic plastic would not represent the crack formation correctly, and the results are therefore not usable.
The stability analysis on columns can be performed with RF‑CONCRETE Columns or RF‑CONCRETE NL. You can find a small example under Downloads.
This example includes the design of a column by the RF‑CONCRETE Columns add-on module. Make sure that the calculation of the internal forces in RFEM is performed according to the geometrically linear analysis and that no imperfections are required because the method used in the add-on module takes them into account.
The example also includes the design with RF‑CONCRETE NL. Here, it is also necessary to calculate according to the second-order analysis and it requires the imperfections in the form of inclinations. For better comparability, the layout of the longitudinal reinforcement was aligned with the result from RF‑CONCRETE Columns, as shown in Figure 01 and Figure 02. Since the reinforcement is optimized by the module after a new calculation, the desired reinforcement was saved as a template (see the red arrow).
In RF-/CONCRETE Columns, a column is designed as a "structural component."When displaying the results "Bending," "Shear Force," and "Bending - Fire Resistance," the resulting maximum value of the design criterion is displayed as a single value at the governing location (x‑location) of the respective design. For example, at the column base, column head, or in the center of the column.If you select the "Highest Design Criterion" result display option, the maximum value of all design criteria is displayed across the entire "structural component" (column).
AnswerFrom the formulae of EC 3‑1‑8, it is obvious that the ultimate tensile forces of the beam end plate are introduced into the column flange, and thus directly into the column web.
Therefore, the upper end plate is not fully stressed by these forces.
For purely structural reasons, the column head plate is available for stiffening and the buckling panel limit, and in case of the required diagonal stiffener, it is used for the transmission of the proportional force that goes into the stiffener.
RF-PUNCH Pro tries to automatically detect the correct geometry of the node of punching shear from the model input and to specify it correctly.Figure 01 - Wall Corner from Downstand BeamsDepending on the entered data, it may be necessary to adjust the preset geometry. For example, because a column is recognized on a wall corner instead of punching shear design. You can change this in Window 1.5, so that the correct punching geometry can be selected, if necessary.
AnswerThe option to enter a taper on a beam can be activated in the Arrangement section of Window 1.4 Geometry. Here you can model the taper on the bottom or top side of the beam.The plate thicknesses as well as the height of the taper are defined by selecting the cross-section of the taper, since the cut rolled cross-sections are often used, for example. If user-defined plates are used, you can select a parametric T‑section. The length of the taper as well as the material are entered in the same section. The weld thicknesses for connecting the taper to the beam can be defined in the Welds section.If there is a tapered member already used as a beam (entered in the "Nodes and Members" section by specifying different cross-sections and lengths), it is not possible to model an additional taper.
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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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