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Frequently Asked Questions (FAQ)
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AnswerEspecially the definition of slippage is a challenge for the solver due to the nonlinear calculation. In the following, hints are given how instabilities can be avoided.
load incrementsWhen considering nonlinearities, it is often difficult to find an equilibrium. Instabilities can be avoided by applying the loading in several steps (see Figure 01). For example, if two load increments are specified, half of the load is applied in the first step. Iterations are carried out until the equilibrium is found. Then, in the second step, the complete load is applied to the already deformed system and iterations are run again until the state of equilibrium is reached. Please keep in mind that load increments have an unfavorable effect on the computing time. A value of 1 (no gradual load increment) is therefore preset in the text box. In addition, you can specify separately for each load case and load combination how many load increments you want to apply (see Figure 02). The global settings are then ignored.
Sliding definitionSlippage (eg in one connection) is defined by means of the "Partial Effect" nonlinearity (see Figure 03). It can be used to define the hinge displacement from which the forces should be transferred. As can be seen in the diagram, the stop, that is, the stiffness that acts according to the corresponding hinge displacement, is considered as rigid (vertical branch, see the red arrows). However, under certain circumstances, this may lead to numerical problems in the calculation. To avoid this, the stiffness that acts after the hinge displacement should be reduced slightly. This is achieved by defining a very stiff spring (see Figure 04).In addition to the very stiff stop, numerical problems may occur within the slippage. In this case, a small stiffness has to be considered for the effect of the slippage in order to increase the horizontal branch a little bit. The stiffness should be selected so small that it has no decisive influence (see Figure 05). This situation is possible by using the "Diagram" nonlinearity.
Arrangement of Member HingesWhen arranging the hinges, care should be taken to ensure that they are not defined in the same direction on both member ends. Thus, there is a state in which the member is not sufficiently supported and the system fails already in the first iterations. In such a case, the slippage on only one side of the member should be defined and the size of the slippage adjusted accordingly (see Figure 06).
You can check the load application with the Project Navigator - Results - Load Distribution. In sections, it is possible to display the load distribution graphically in a graphic representation of the perimeter and height.
Figure 1 shows a free variable load on a cylinder along its circumference. Figure 2 shows a free variable load by height. The load distribution can be clearly seen by the load distribution in the horizontal and vertical section.
AnswerThe cause may be the definition of member eccentricities. For a better overview, the origin lines are automatically hidden for eccentric members. In some cases, it may appear that a member end is not sufficiently supported (see Figure 01, left). However, the meshed line acts in the background. This can be clearly shown by hiding the members in the Display navigator (see Figure 01, right).In Figure 01, the line at the common node has not been geometrically separated. For this reason, no graphical connection line that represents the eccentricity results in this case. However, because of the setting shown in Figure 02, the node is still networked with the vertical member.To visualize the graphical connection line, it is recommended to divide the member or line at this node (see Figure 03)
AnswerSince the equivalent member designs of Eurocode 3 have different interactions than are the case for the designs according to the partial internal prescalcision method and a mixture of these different designs is not desired for reasons of clarity, RFEM deactivates the equivalent member designs when using the RF- / STEEL Plasticity add-on.
The polyline shown in Figure 1 was created in the order of Nodes 1 → 2 → 3 → 4 → 5. This is also shown in column B "Node No." Table "1.2 Lines". Thus, the line segments between nodes 3, 4 and nodes 4, 5 overlap so that the error message shown in Figure 2 is displayed.
The order of the nodes must be changed so that no line segments overlap. In this example, we want to specify the order of Nodes 1 → 2 → 3 → 5 → 4, as shown in Figure 3.
You can also use the "Disassemble Polyline" function to decompose the polyline (Figure 4). Then, two lines are created between nodes 5 and 4. Then, delete a line. You can also use the "Regenerate Model" function in the "Tools" menu.
Both approaches are shown in the video.
AnswerThe message shown in Figure 1 appears when you try to open the dxf file by using the File → Open menu option or the corresponding toolbar button. To import the dxf file, select File → Import from the menu (Figure 2). Importing a dxf file is shown in the video.
AnswerCurrently, the plasticity for 1D elements only works in relation to the normal stresses in a member, which means that only an interaction between axial force and moment is possible. The shear force interaction is not taken into account. In addition, the stresses from shear force are only calculated elastically. When using one of the plastic material models, it is also important to ensure a sufficient division of the elements, because a cross-section is generated internally on each Gauss point on the member element where the stress is calculated and, if necessary, a stiffness reduction for redistribution of internal forces is performed. If, for example, the number of divisions is increased, the model may become unstable because the redistributions of stresses can not be carried out any longer, which means that the loading in the cross-section is too high.It is generally recommended to use a division of 50 for member elements when using the plastic material model.
AnswerThe program VERBUND-TR for the design of composite girders is designed according to ENV 1994-1-1: 1992-10. This standard specifies a composite cross-section consisting of steel sections and reinforced concrete.The design according to EN 1995-1-3 is carried out for the design of composite beams consisting of timber and reinforced concrete. In this case, the time-dependent load conditions t = 0, t = 3-7years and t = infinite have to be analyzed in particular. These states are usually taken into account by means of impressed strains. This is done in the RFEM Manual program. For this and many other reasons, it is not possible to design timber-concrete composite beams in the VERBUND-TR program.However, on our homepage you can find a lot of information about the design of timber-concrete composite beams, for example here.
AnswerNo, this option does not necessarily have to be activated to consider the self-weight. If the masses are imported from a load case that already contains the dead load, this option must not be activated. Otherwise, the structure's own weight is doubled.
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