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Frequently Asked Questions (FAQ)
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If two members are hinged to each other, the corresponding release must be assigned to only one of these members.
If there are three members, which are all hinged, two of the three members will have the corresponding release.
Generally, a nodal point with a completely pinned design with an arbitrary number of member ends receives a total of one member hinge less than the existing number of member ends:
Number of member ends: n
Number of Member Hinges for Completely Hinged Connectors: n-1
Bei weniger als n-1 Stabendgelenken sind die jeweiligen Stabenden ohne Gelenk biegesteif miteinander verbunden.
Bild 1 zeigt drei Varianten eines Hauptträgers, an welchen ein Nebenträger anschließt:
Wird ein Stabendgelenk zuviel angesetzt, so kann es zum Abbruch der Berechnung aufgrund von Instabilität kommen. Demnach ist die oben beschriebene Regel zu beachten.
- Vollständig biegesteife Verbindung - kein Stabendgelenk
- Teilweise gelenkige Verbindung: Der Nebenträger schließt gelenkig an den durchlaufend biegesteifen Hauptträger an - ein Stabendgelenk
- Vollständig gelenkige Verbindung: Alle drei Stäbe schließen gelenkig aneinander an - zwei Stabendgelenke
The RF-FORM-FINDING add-on module has two form-finding types that you can alternatively assign to each start surface input.The first option named "Standard" moves the relevant FE nodes in all three spatial directions X, Y, Z until the membrane's constant, specified surface tension is in equilibrium with the boundary reactions.The second option "Projection" keeps the relative horizontal X', Y'-position of the FE nodes in relation to the normal plane of the surface tension relation axis and only displaces the vertical Z'-Position perpendicular to the plane until the surface tension modified by the membrane is in equilibrium with the slope Peripheral reactions is completed.In general, the "Standard" method is the right choice for all non-tapered models. In the case of conical membrane shapes, using the standard method results in an ambiguous situation. In this case, the tangential stress component of the surface tension is mutually exclusive due to the circular arrangement and displaces all FE nodes, irrespective of the radial position and surface stress magnitude, to reach the global equilibrium with consideration of the radial prestress component on the cone axis. In this case, the Projection method must be selected to achieve a continuous conical shape. The resulting shape then holds a non-uniform final surface tension due to the projected surface tension specification.
AnswerWith the model check, members that cross each other but do not have a common node at the point of intersection can be found (see Figure 1). To check the model, select Tools -> Model check -> Opening or closing intersecting members.
The results are shown in the "Groups of Crossing Not Connected Members" dialog section. The crossing members are listed in groups; the current group is represented by a
The "What is to be done with" dialog section controls how the crossing members are handled. The "Connect members" option is suitable for actual transfer options for internal forces, but not for For example, for usual diagonal crossings with tension members.
Alternatively, it is also possible to use the model check to display the member pairs as an Excel list or to create visibilities. The visibilities created in this way can be quickly used to find and delete relevant members in the model.
AnswerThe nonlinear contact between member and membrane can be done by a set of member elements between the member and the surface. This requires that the member lies eccentrically in the plane of the compressive force resulting from the membrane effect and the connection line of the membrane connection. The geometric distance between member and membrane itself has to be aligned to the physical distance between member axis and membrane connection.To ensure that the coupling runs homogeneously over the entire coupled length, it is necessary to ensure a uniform arrangement with the same number of FE nodes on the member axis and on the projected contact line on the membrane surface. This division and orientation of the FE nodes is achieved by placing the corresponding topology nodes on the member axis and the corresponding line of contact on the surface. The distance of the Topology Node affine to the selected mesh size of the connected Membrane Surface should be selected.The coupling itself must be designed with a rigid member failing nonlinearly under compressive load between the resulting nodal pairs. In this case, the specified nonlinearity must be implemented with a member nonlinearity "Failure under tension". The connection of the rigid member in the area of the eccentric member is completely compatible (bending-resistant) and must be carried out with a free translational hinge related to the rigid member axis in the y / z axis in the area of the membrane.Due to the selected nonlinearity and the alignment with the compression force resultant in connection with the free translational hinge, this contact modeling is able to transfer only compressive forces to the connected cross member. In case of a suction load, the coupling components fail and the membrane moves away from the cross member without hindrance.
AnswerThe display of the midpoint of a circle, arc, ellipse, etc. can be controlled in the Display navigator of the Project navigator. Displayed in the Model -> check box Lines -> Activate center points (see Figure 1). The center point can also be caught.
You can realize such a connection with a line release. Figure 1 shows an example model where wall 1 should transfer only compressive forces to wall 2.
First, the dialog box for creating a line release is opened (fig. 2). In the dialog box (Fig. 3) Now select the lines for release and type. The Type must also be created. The coordinate system of the line specifies the direction so that "If vy positive" must be selected as release (Fig. 4).
Figure 5 and 6 show in two load cases, how the line release works.
AnswerIt is often the case that one or more surfaces of the generated volume have double lines. In this case, the peripheral surfaces of the solid are not closed and the generation must be stopped. To find these lines quickly, the program displays a corresponding message.Solution:You can quickly find double lines with the function "Tools → Model Check → Overlapped Lines". In this tool, you can also display the line pairs as an Excel list or create partial views (see highlighted buttons in Figure 02).However, it is often the case that the lines can not be deleted easily because they are assigned to different objects. If you delete one of the lines, z. For example, a surface is deleted as well. It is therefore recommended to check for all structural components if the lines can be deleted and if necessary change the boundary lines.
AnswerIn most cases, ceilings or walls are connected with each other in a hinged manner so that moments from the floor slab are not transferred into the walls. If a line hinge and a downstand beam (rib) are also assigned to the same line, it is important to which surface the line hinge has been assigned.Solution:As the rib is usually assigned to the floor slab, the line hinge should be assigned to the wall (see Figure 1). If this is not the case, an error message appears (see Figure 2) and you still have to abort the creation of the rib.The same is true for line hinges on free slab edges. If a line hinge was created by mistake, RFEM also displays an error message when creating the rib (see Figure 3 and Figure 4).
AnswerIt is possible to realize a scissors hinge between surfaces by means of line releases. In the attached model, a line release has been created on line 5, which releases surfaces 3 and 4. Since surfaces 3 and 4 also automatically refer to the newly generated line 8, the scissors hinge is correctly defined.
AnswerWhen you design glass with the RF-Glass add-on module, the layer structure is defined in the add-on module (Window 1.2). The layer structure in the main window of RFEM is irrelevant here, because the add-on module creates a temporary calculation model during the calculation. It is only important that the surface stiffness is set as glass (see Figure 1).The same applies to the support of the wall. It is also performed completely in RF glass.We already have an interesting webinar about RF glass with the topic "Design of Glass Structures in RFEM" on our website.
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