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Frequently Asked Questions (FAQ)
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AnswerYes, you can also use the RF-CONCRETE Surfaces add-on module to design coffered ceilings, ribbed floors, or hollow core slabs. The design is possible for the ultimate limit state.
The ceilings can be created as orthotropic surfaces in RFEM (see Figure 01).
A detour in RFEM is possible.The soil pressure from which the bending moment is determined for the design by means of integration can be applied as an "external load" in an RFEM equivalent model.Compression Distribution in RF-/FOUNDATION ProThis compressive stress can be applied to a replacement system in RFEM as a "Free Surface Load".In this case, the equivalent system is a rigid surface. The size of the surface depends on the position of the design section set in RF-/FOUNDATION Pro. In this case, we set "in column center".With this equivalent system, it is possible to recalculate the "moment from compression stress distribution" determined in RF-/FOUNDATION Pro.You can download the example described above using the link below and open it in RFEM 5.
AnswerThe theoretical approaches for this can be found in "Fritz Leonhardt, Lectures on Concrete Structures, Third Part, Third Edition" be understood.Special attention must be paid to Chapter 16.3 "Single Foundations for Columns".
The stiffness modifications can be controlled separately for the following elements:
The first option "Materials" is activated only for load combinations by default (see Figure 02), because the second-order analysis is preset here. If this function is activated, the stiffness of all elements is reduced by the partial safety factor of the material (see Figure 03). This is especially important in timber construction in Europe. If the automatic load combination was selected for the standard EN 1990 + EN 1995, SIA 260 + SIA 265 or DIN 1055-100 + DIN 18008, the result is different default settings. If the partial safety factor of the material is defined as 1.0, it does not matter if the function is activated or not.
Use this option to control the multiplication factors for individual cross-sections. In the "Modify" tab of the Edit Cross-Section dialog box, you can modify the moments of inertia as well as surfaces of the cross-section. This has an influence on the stiffness of the cross-sections.
If you edit a member, the "Modify Stiffness" tab appears. There are different definition types (see Figure 05). The "Multiplier factors" option allows you to modify the stiffnesses of single members in the same way as for the cross-sections.
For surfaces of the "Standard" and "Without Tension" type, you can manipulate the stiffnesses of the surface in the "Modify Stiffness" tab of the "Edit Surface" dialog box. There, as in the case of orthotropic surfaces, you can modify the elements of the stiffness matrix with a factor.
Further possibilities of stiffness modification
In addition, you can select another option in the Calculation Parameters to modify specific stiffnesses for other elements (see Figure 07). When you activate the "Modify Stiffnesses" option, a new tab appears (see Figure 08). In addition to the member and surface stiffnesses, it is also possible to manipulate the stiffnesses of supports and hinges.
Interaction of individual factors
If several factors have been defined for an element (for example, from the cross-section and the member), they are simply multiplied by each other. The result for the example shown in Figure 09 is as follows:
Global control of stiffness modification
In the global calculation parameters (see Figure 10), you can deactivate all options mentioned above at once. The local settings in the calculation parameters of the load cases or of the load combinations are ignored.
AnswerYou will find an option in the "Settings" of the add-on module (see picture 01).
AnswerIn RFEM, the graphical results are smoothed on the basis of the results at FE mesh points. The results are transferred to REVIT on the basis of the results on grid points. In RFEM, the grid for the surfaces is set to 0.5 m by default. Set a fine grid for the surfaces and the graphical display of the results in RFEM and REVIT is comparable.
Only the default setting of 1 load increment can be set when a complex nonlinear material model is defined. The reason for this is because the program cannot determine the correct material stiffness for each incremental loading amount. The exact maximum load needs to be applied to the structure in order to determine the state of the material's stress/strain diagram.Figure 01 - Material Model - Nonlinear material definedThis setting can be found and changed under "Calculation Parameters" as well as under the "Calculation Parameters" in the load cases and combinations dialog box.
In this sense, 'EC2 for RFEM' is not an add-on module that you can start separately, but a standard according to which you can design reinforced concrete structures e.g. in RF-CONCRETE Surfaces or RF-CONCRETE Members.The selection of the design standard can be taken from the 'General Data' dialog box of the respective module.The same applies to 'EC2 for RSTAB'.A design standard, here the 'EC2', is required in the following add-on modules:- RF-CONCRETE in RFEM 5- CONCRETE in RSTAB 8- RF-/CONCRETE Columns in RFEM 5 and RSTAB 8- RF-PUNCH Pro (only available for RFEM 5)
AnswerBoth RFEM and RSTAB are available as solutions. In addition to Eurocode 2, international standards such as ACI 318, CSA A23.3, SIA 262 or GB 50010 are also available for the designing in both programs.
With additional modules for columns, foundations, or punching shear designs, it is possible to calculate the components quickly and reliably.
Main Programs RFEM or RSTABThe main programs RFEM or RSTAB are used to define structures, materials, and Actions.
RFEM is clearly the first choice for solid structures, since in addition to the possibility of creating spatial frame structures, structural systems consisting of plates, walls and shells can be created as well. RFEM is the more diverse variant, as it can be equipped and extended with appropriate additional 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 nominal curvature method
- RF-PUNCH Pro
Punching Shear Designs of Surfaces
- RF-/CONCRETE 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 earthquake calculations or vibration analysis of the building are necessary, the RF-/DYNAM Pro Add-on Modules provide suitable tools for determining natural frequencies and shapes, forced vibration analysis, generation of equivalent loads or also for nonlinear time history analysis.If you have any further questions on the Dlubal 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 with 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.
A stability analysis on columns can be carried out with RF-CONCRETE Columns or RF-CONCRETE Members. You can find a small example in 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 first-order analysis and that no imperfections are required because the method used in the module takes them into account.
The example also involves the design by means of RF-CONCRETE NL Members. Here again, it is necessary to calculate according to the second-order analysis and imperfections in the form of inclinations are required. For better comparability, the layout of the longitudinal reinforcement was aligned with the result from RF-CONCRETE Columns, as shown in Figures 01 and 02. Since the reinforcement is optimized by the module after a new calculation, the wanted reinforcement was saved as a template (see red arrow).
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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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