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Frequently Asked Questions (FAQ)
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AnswerIn RF-/JOINTS Steel - Rigid, the design according to EN 1993-1-8 Chapter 6.2.7 Equation 6.24 is implemented. If the acting axial force exceeds 5% of the plastic resistance N pl, Rd , Equation 6.24 is used.
AnswerDuring the development of the FRAME-JOINT Pro add on module, the lower end plate extension was fixed because it results in an improved load transfer of the compressive force into the column.
It is not possible to deactivate the extension and its minimum dimension is defined as follows:
uu = max
- End plate thickness
- √2 * bottom flange weld
- for end plate depths < 200 mm → min 10 mm
- for end plate depths > 200 <400 mm → min 20 mm
- for end plate depths > 400 → min 30 mm
AnswerFrom the formula of EC 3-1-8, it is obvious that the ultimate tension forces of the beam's 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 end plate is available for the stiffening and the panel boundary and serves for the transmission of the proportional force flowing into the stiffener in case of a required diagonal stiffener.
AnswerTo enter a taper on a beam, it is necessary to select the Layout dialog section. A taper can be modeled either on the bottom side or on the top side of the beam.The plate thicknesses, as well as the height of the taper, are defined by selecting a tapered cross-section, since, for example, repeatedly cut rolled cross-sections are used. If any plates are used, a parametric T-section can be selected. The length of the taper, as well as the material, are entered in the same dialog section. The weld thicknesses for connecting the taper to the beam can be defined in the Welds dialog section.If a tapered member is already used as a beam (entered in the 'Nodes and Members via Different Cross-Sections and Lengths' section), it is not possible to model an additional taper.
AnswerThe easiest way is to change to the design notes after having made the calculation or when the note appears in the design notes (see Figure 2). In this case, it is demonstrated there that the width of the end plate is not correct. When changing to the input window 1.4.2, it is possible to quickly recognize in the graphic that the value is not within the allowable range.This can be corrected very quickly by adjusting the horizontal bolt spacings (see Figure 3).
AnswerThe RF-/JOINTS add-on module is divided into several joint groups. For this, see the following FAQ.Therefore, there is no straightforward answer to the special aspects of the design as in this FAQ.In contrast to the RF‑/TIMBER Pro add-on module described in the mentioned FAQ, however, it is obvious that the RF‑/JOINTS add-on modules cannot design EC2, even if manually changing the LDC, for example in the RF‑/JOINTS Timber - Steel to Timber add-on module (see Figure 01).Furthermore, this also applies to the add‑on modules RF‑GLASS and RF‑/CONCRETE NL.The reason for this is that there are stiffnesses exported in the program in the case of some joint groups of the RF‑/JOINTS add‑on module. For nonlinear calculations, the superposition with result combinations is not allowed. In the case of the second result combination mentioned above, there is the special feature that the superposition is no longer conservative, even in the case of simple structures. The design cannot be also performed correctly by manually changing the LDC.Nevertheless, if a result combination should be superimposed with constant and alternative additive, it is necessary to split EC2 in the attached file into load combinations as follows.
- RC2*=CO1 or CO2
AnswerIn addition to geometry input errors, the cause is usually the different calculation principles of both modules.The design of an end plate joint with the RF-/JOINTS Steel - DSTV add-on module is carried out by comparing the saved ultimate load capacities with the design internal forces. The underlying load capacities are taken from the current DSTV guidelines.When using the RF-/JOINTS Steel - Rigid add-on module, the capacities of the connections are calculated according to DIN EN 1993-1-8 by means of the component method. Thus the results can be directly influenced by the used settings.By default, an elastic distribution of bolt forces is used as a basis. By selecting a plastic force distribution in the connection, you can activate additional load capacities. They are already included in the limit load capacities according to the DSTV-guideline.Therefore, to obtain comparable results between both add-on modules, a plastic distribution of forces must be applied for the calculation. In addition, it is important to ensure a correct modeling of the connection geometry.
AnswerSpecifically, for the "Column web, Compression Force, Bottom" design, a specified web stiffener is only applied to the design if it is actually required, or if the design without web stiffener cannot be performed. In the latter case, the comment "Web Stiffener Needed" appears in the last column of the results table.It is also important to note whether a continuous rib or a partial rib is applied.In the case of the partial rib, the compressive force is divided into web and rib and thus designed.If a continuous rib is used, the column web is first fully loaded and the excess load is applied to the rib. In the case of T-joints and cross joints, this approach prevents the rib from being overloaded.
AnswerThe most common causes are listed below:
1. SingularitiesSingularities appear in a limited range due to a concentration of the stress-dependent result values. They are conditioned by the FEM methodology: Theoretically, the stiffness and/or the loading in infinite magnitude are concentrated on an infinitesimally small area. Singularities therefore occur, in particular, at punctiform supports, load application locations, reentrant corners, or in the area of stiffness changes.If the result value of the stress peak is larger and the area of this stress peak is smaller for a finer FE mesh, a singularity is very likely to occur.When handling singularity locations it is recommended to follow articles of our Knowledge Base:
2. Unrealistic support definitionRigid supports (infinitely stiff supports) are rather unrealistic in many cases. Therefore, it is recommended to display the supports as elastic supports. In this case, the stiffness of adjacent structural components should be estimated realistically.The deformation diagram, possibly with a pronounced precamber, and the output of the support reactions or contact stresses are suitable for checking purposes. For a better overview, the simplest possible loads should be used for the check.Often, a mistake in the direction definition, for example of loads, member hinges, or line and surface releases, is the cause of unrealistic behavior. When using local or rotated coordinate systems as reference systems, particular attention must be paid to the correct definition. For example, nonlinearities defined in the opposite direction are typical for supports that fail due to tension or compression.Incorrectly defined loads can be easily identified by displaying the loading. The loads applied for the calculation can be conveniently displayed in the Results navigator by using the "Load Distribution" option.Furthermore, modeling inaccuracies can lead to incorrect definition of directions. By importing a DXF file, you can introduce inaccuracies into the model, for example, nodes that are not on top of each other or lines skewed in the wrong direction.The function "Regenerate Model" is very helpful for the treatment of minor inaccuracies.Incorrectly defined releases and hinges can usually be identified by means of the deformation graphic and the diagrams showing the distribution of internal forces. Again, it is recommended to work with simple loads for checking purposes.
4. Model does not correspond to realityOften it can happen that not all external or internal influences from a structure to be modeled have been considered sufficiently and accurately in the model. Supports or supporting structural components may not have been modeled or it happened in the wrong place. The realistic estimation of the stiffness of adjacent structural components is also important. Provided that it has been over- or underestimated, the load transfer in the model is sometimes significantly changed.However, a simple check of the deformation, possibly with a pronounced precamber, is possible.The following questions may help to find a solution if the real structure is known: Is the magnitude of the deformations realistic? Is the deformation diagram qualitatively consistent with my expectations?A good example is presented in the following Knowledge Base article:
AnswerThe result values described in RFEM as "Contact Stresses" are by definition reserved for surfaces with surface supports (see RFEM Manual).Instead, contact solids can be evaluated like standard solid elements. According to the definition of the contact solid axis system, it is thus possible to display the stresses in the contact direction as well.Please note that for the evaluation of contact solid, the option "Remove Contact Solid from Display" must be deactivated in the Display navigator (see Figure 2).
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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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