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Frequently Asked Questions (FAQ)
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AnswerBoth RFEM and RSTAB are ideally suited for use in mechanical engineering and are used by numerous users in daily practice. Due to the modular structure, you only need the add-on modules required for your applications.
Main Programs RFEM or RSTABThe basic programs define the structures and materials as well as the actions.RSTAB supports you best when it comes to truss or frame-type structures
In addition, RFEM provides the best support if you want to additionally calculate structures with surface or solid elements.
Dynamic AnalyzesIf seismic calculations or vibration analyzes are necessary, the RF-/DYNAM Pro add-on modules provide suitable tools for the determination of natural frequencies and shapes, the analysis of forced vibrations, the generation of equivalent loads, or for the nonlinear time history analysis.If you have any further questions on the Dlubal programs, please do not hesitate to contact the sales department.
Calculation of stresses and comparison with the limit stresses
Modeling of Pipe Tilts (only in RFEM)
- RF-PIPING Design
Design of Pipelines (only in RFEM)
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).
For the example shown in Figure 01, no load distribution is displayed between the outer facade elements. Unloaded cells are not displayed according to the color scale during load distribution, but remain empty. Thus, the value on these elements is 0. This has the advantage that it is recognized immediately that the FE elements are not stressed.The cause of the problem can be visualized directly in RWIND Simulation. By default, calculations are based on a simplified model. Depending on the setting, it is possible to refine or coarsen the shell of the model. An FE mesh is placed over the structure, so to speak, and depending on the level of detail, this FE mesh snuggles against the model. Figure 02 shows the extent of the degree of detail that is too small. The surfaces standing on the façade are not displayed well enough and no wind flows between the cantilevered surfaces in the simulation, which is why these internal surfaces do not experience any wind pressure.The degree of detail can be adjusted in RWIND Simulation by "Edit Model" or directly in RFEM in the settings for the wind load simulation (see Figure 03). Optionally, the simplified model can also be completely deactivated in RWIND Simulation.In the case of a greater degree of detail (corresponds to a finer FE mesh), the cantilevered surfaces are displayed cleanly and the FE elements are stressed accordingly (see Figure 04 and Figure 05).
You can query the surface area by using the shortcut menu.Right-click on any surface of the entered structure. In the shortcut menu, you can find the entry "Centroid and Info ..."In the dialog box that appears, you can find the available information about this surface.There you can find z. For example, the surface area or the weight.Optionally, you can also create a node in the centroid of the selected surface. A multiple selection of surfaces is also possible.
AnswerIn a short overview, creating hold down elements involves modeling rigid links and adding in nodal supports with non-linearity settings that allows the supports to take only tension forces. A line support is added at the bottom of the wall that only takes compression forces. The individual nodal supports connected with rigid members only take tension forces.
A more detailed look on how these elements can be model can be seen in the video below.
AnswerThe default definition of surface elements assumes an isotropic material behavior. The load attempts to get to the supports as quickly as possible. The stiffness of the elements also plays a role here.
For plates, the structural behavior or the load transfer is best represented and understood with the trajectories of the principal moments αb. For wall elements, it is necessary to consider the trajectories of the principal axial forces αm.
In this example, the load is not applied parallel to the free plate´s edges but almost perpendicular to the supports, because this is the shortest path of the load transfer.
At the blunt corners of the system, the load absorption area is larger than in the support centers, corresponds to a singularity point and has -as a consequence of that- large peak values.
In order to force the system to remove the load parallel to free plate edges, the following procedure is the fastest:
Definition of an orthotropic plate. It is recommended to use the orthotropy type 'Effective Thicknesses'. The effective plate thickness has to be specified in the support direction and a very small thickness (e.g. 1mm) in the secondary support effect.
The second graphic shows the difference between both models.
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.
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.
Yes, the AISC module will detect if there are bending or torsional forces on a member and design accordingly per Design Guide 9. The add-on module combines the shear stresses due to bending and axial loads calculated by RFEM and shear stresses calculated using St. Venant's Torsion to make design checks per Design Guide No. 9.The Steel AISC module also has the option under "Details" to activate the RF-STEEL Warping Torsion add-on module extension where a nonlinear warping torsion analysis is performed using 7 degrees of freedom. Normal and shear stresses on the member are independently determined from the AISC Design Guide No. 9. The loading used in this extension is taken directly from RFEM for analysis.
AnswerAccording to the default setting in the program, it is defined that the loads act on all surfaces.However, if there is no surface available in the file, the load cannot act and a warning will be displayed. If the message is confirmed by clicking 'OK', the load is still imported into the model but not applied to any surface. However, as soon as a surface is subsequently defined, the imported loads can act on it.
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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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