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Frequently Asked Questions (FAQ)
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AnswerMany webinars and online videos explain the automatic load combination, for example, for Eurocode. An example of this can be found directly on YouTube here.However, due to time reasons, these webinars and videos often do not include any accidental combination, such as those necessary for a fire situation or earthquake.Such a combination can be generated just as easily and flexibly as the combination for the ultimate limit state (ULS) or the serviceability limit state (SLS).The generation of it is shown in the attached video.In summary, the following steps are necessary (the structure and load cases are already defined):
- Activating the automatic generation of combination in General Data (Figure 01)
- In the Combination Expressions tab, select the accidental combination with psi1 or psi2 as leading (Figure 02).
- Ideally, create the combinations with an enveloping result combination.
- Select the created result combination for design in the add-on module, for example RF-/TIMBER Pro, under the "Fire Resistance" tab.
In the details of all add-on modules, you can control the display of result tables. In this case, it is helpful to only display the results by load case or by material.
In the RF‑STEEL Surfaces add-on module, it is also possible to perform the calculation of enveloping values only.
Furthermore, it may be helpful to display the results in grid points. For the RF‑LAMINATE add-on module, it is also possible to completely hide the results of the grid points. A detailed description of this can be found here .
The settings for the RF‑STEEL Surfaces add-on module are shown in Figure 01.
AnswerRFEM uses OpenGL for the graphical display. If available, RFEM uses the hardware acceleration of the graphics card. If this does not support hardware acceleration, RFEM uses the software implementation of Windows OpenGL.In the case no hardware acceleration can be used, the graphical display is considerably slower. The extent to which this has a negative effect on the usability of RFEM depends on the size of the processed RFEM models.For many (not all) hypervisors, it is not possible to use the hardware-accelerated OpenGL. RFEM would basically run in the virtual machine. However, the graphic display would be slower.We recommend to test on a typical RFEM model whether the speed of RFEM in the virtual machine is acceptable.Please note that our Support can only help you to a limited extent when using virtual machines.
AnswerThe calculation of the results in grid points is important for displaying values on surfaces, among other things. You can find the information about grid points here.The problem is that in the case of complex structures and many load combinations, the calculation in grid points is relatively time-consuming and therefore, it requires a large amount of memory. Even if you perform the calculation in FE nodes as shown in Figure 01, it is always necessary to additionally perform the calculation in grid points. Otherwise, the results cannot be displayed in grid points under Values on Surfaces.For complex structures, it is recommended to deactivate this option to perform a faster calculation.
If activating the automatic combinations in General Data, the actions, combination expressions, action combinations, and load or result combinations are created automatically. In this case, some default settings have been selected by the program developers, which apply in most cases.
By default, the following design situations with the respective combination expressions are generated:
- ULS: Ultimate limit state for permanent or temporary situation
- SLS: Serviceability limit state for characteristic situation
- SLS: Serviceability limit state for frequent situation
- SLS: Serviceability limit state for quasi-permanent situation
If load cases of the "Accidental" or "Earthquake" type have been defined, they are not considered in the preset combinations. For these load cases, it is necessary to create a new combination expression manually. You can select the appropriate design situation in the list.
Accidental load cases are only used in the "Ultimate Limit State - Accidental" or "Earthquake" expressions.
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.
AnswerFor seismic design, the add-on modules RF-/DYNAM Pro - Natural Vibrations and RF-/DYNAM Pro - Equivalent Loads are available. They allow you to perform the multimodal response spectrum analysis. After the analysis in the add-on modules, the calculated seismic loads are exported to load cases, which can be evaluated as usual.Furthermore, you can evaluate the story drift and the horizontal shear of the building. These and other features are described in detail in the webinar "Response Spectrum Analysis in RFEM."
Yes, it is possible by using the load generator.In the "Tools" menu, you can find the "From Motion..." command under "Generate Loads."In the "Generate Loads From Motion" dialog box, you can define the acceleration a in [m/s²], which can be used to determine a load, depending on the mass of the structure.In RSTAB, it is thus possible to generate a load on a member. In RFEM, on a member, surface, or solid.Important: The program uses the dead load of the structure. The mass of a specific load case cannot be applied here.
AnswerThe following code shows how to get different calculation parameters via the COM interface. It also shows how to specify the setting for deactivating shear stiffness:' get model interfaceSet iApp = iModel.GetApplication()iApp.LockLicense' get calculation interfaceDim iCalc As RFEM5.ICalculation2Set iCalc = iModel.GetCalculation' get surface bending theoryDim calc_bend As RFEM5.BendingTheoryTypecalc_bend = iCalc.GetBendingTheory' get settings for nonlinearitiesDim calc_nl As RFEM5.CalculationNonlinearitiescalc_nl = iCalc.GetNonlinearities' get precision and tolerance settingsDim calc_prec As RFEM5.PrecisionAndTolerancecalc_prec = iCalc.GetPrecisionAndTolerance' get calculation settingsDim calc_sets As RFEM5.CalculationSettingscalc_sets = iCalc.GetSettings'get calculate optionsDim calc_opts As RFEM5.CalculationOptionscalc_opts = iCalc.GetOptions' set ShearStiffness to falsecalc_opts.ShearStiffness = FalseiCalc.SetOptions calc_optsUnder Downloads, you can find the EXCEL macro.
In "Global Calculation Parameters," there is the setting 'Number of divisions of members for result diagrams."By default, this value is preset to "10."If the members with very different lengths are used in a model, it may happen that the preset value of "10" is too small. This may cause that the parabolic moment distribution is not displayed correctly for the shorter members.To avoid this problem, enter a higher value, for example "50."Thus, a parabolic moment distribution is also displayed on the shorter members.The length of the sections is based on the length of the longest member in the structure divided by the defined number of member divisions. The finer division of members applies to all members of the model.
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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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