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Frequently Asked Questions (FAQ)
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For a resultant, a concrete combination of loads is required, which result combinations can not provide.
The following example shows the problem quickly. A single-span beam is loaded with three different load cases. For the support at node 1, the result envelope of the 6 possible load combinations results in a maximum PZ of 11.25 kN from the result of CO 2 (see Figure 01). The support at node 2 has a maximum PZ of 12 kN from the result of CO1. However, the resultant of 23.25 kN does not occur in any of the involved load combinations and is therefore too large (maximum CO 1 and CO 2 with 22.5 kN).
The situation is similar with the pure result combination from the load cases, which have the same maximum values PZ of the nodal supports 1 and 2. However, it is not apparent here that a resultant would give incorrect results.
For result combinations, resultants are not used for result combinations because the results may be incorrect.
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.
The structural behavior or the load transfer is best represented and understood with the trajectories of the principal moments α b for plates. For wall elements, consider the trajectories of the principal axial forces α m .
In this example, the load is not applied parallel to the free plate 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 application area is larger than in the support centers, corresponds to a singularity location and thus results in 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. The "effective thicknesses" orthotropy type is recommended. Thickness of the actual plate thickness is specified in the support direction and a very small thickness (for example 1mm) in the secondary load.
The second graphic shows the difference between both models.
AnswerIn general, an imperfection describes the imperfection of a structure or the deviation due to its production from the ideal shape. There are different ways to simulate the imperfection. In RSTAB and RFEM, imperfections are represented as equivalent loads. The definition of equivalent loads is shown in Figure 01 and is taken from  . The same is described in EC3  . Since these are equivalent loads that are dependent on the axial force, they are also taken into account for a calculation according to the linear static analysis. It is recommended to manage loads and imperfections in separate load cases. They can be suitably combined with each other in load combinations. For the load case general data (see Figure 02), load cases with pure imperfection loads have to be classified as the action type "Imperfection".
AnswerThe graphic display of the nodal displacements and rotations is made via the entry GlobalControlling deformations in the Results navigator. Additionally, there is a possibility to display the deformations not only as lines but also as colored cross-sections in the Project Navigator.
AnswerTo be able to consider this non-linearity, it is possible to use the "Partial Activity" function (see Figure 01). This way you can define the limit moment beyond which any other moments will be taken into account.
AnswerIn the RF-/STEEL add-on module, an equivalent stress design is performed according to von Mises. An elastic stress design (EL-EL) is to be made. In RF-/STEEL EC3, a classification is carried out before the design. If the cross-section is classified as class 1 or class 2, the design is performed against plastic limit internal forces. An EL-PL design is performed. If you do not want to use the plastic load reserves, you can switch the design to EL-EL in the details of the RF-/STEEL EC3 add-on module. The results are then comparable with RF-/STEEL.
AnswerThe sag can be influenced by the prestress of the membrane. Please note that a uniform increase in both directions does not cause any changes in the shape. Thus, a modification must only be made in the desired direction. The video shows the procedure.
When displaying the result values 'Values on Surfaces', there are two distinctions.The result values are displayed either on the 'Grid and User-Defined Points' or on the 'FE Mesh Points'.When displaying the 'Grid and User-Defined Points', the results are displayed in the distance of the grid points.The distance of the grid points is a property of the surface and can be controlled in the 'Edit Surface' dialog box.Alternatively, you can display the result values in 'FE Mesh Points'.The number of FE mesh points depends on the generated FE mesh size.You can control the displayed color gradient by selecting the option 'Internal Forces/Stresses' in the Display navigator. See the FAQ below.
In the 'Global Calculation Parameters', there is the setting 'Number of Member Divisions for Result Diagrams'.By default, this value is preset to '10'.If members with very different lengths are used in a model, it may happen that the preset value of '10' is too small. This is then reflected, for example, by the fact that the parabolic moment diagram is not displayed correctly for the shorter members.To avoid this problem, enter a higher value, e.g. '50'.Thus, a parabolic moment diagram is also displayed on the shorter members.The length of the sections results from 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.
Currently, there is no direct way to determine the limit load. It is important that there are also several different states and thus that there can be several local limit loads.
You can assign load steps to a structure and retroactively view the individual load steps and thus find a load factor near a post-critical failure (depending on the number of load steps).
In the attached model, 20 load steps and saving of the intermediate results have been set (Figure 01). In Figure 02, the load step 10 is displayed as the last load step before the post-critical failure, and in Figure 03, the first load step after the post-critical failure is visible, whereby the deformation is significantly higher.
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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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