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Frequently Asked Questions (FAQ)
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AnswerFor rod end joints where the reference system is related to the local rod axes, the joint is placed directly on the rod end or rod end. If the joint is to act directly at the node, the reference system must be related to the global axis system.
AnswerBasically, elements in RFEM are rigidly connected. To solve this problem, two elements are suitable in RFEM. The line joints and the line releases. The difference is explained in the link below.
AnswerIf you define line loads on a line that is decoupled from the overall system, that line becomes compliant. The program checks this incorrect entry and gives a hint (Fig. 1). However, there are structures where this line is kept at a different point. In this case, the program continues to calculate after the user has confirmed the note. However, since the deformation for such a decoupled line becomes very large, it is not displayed in the graphic output.We generally recommend not to load lines that are decoupled via a line release or line joint.The theoretical background will be explained in this article .
AnswerAxial / transverse joint or springThe degrees of freedom are based on the following definition of the axis system: The axis x points in the direction of the line;the axis y represents the tangent to the surface plane, the axis z the normal to the surface.The text boxes and table columns control the degrees of freedom for axial and shear forces. Is aCheckbox, this means that the shift in this direction is possible andthus the power is not transferred. It can also be entered the constant of a Wegfederbecome.Torque joint or springThe degrees of freedom of the moments are related to the local joint coordinate system (axisx in the direction of the line, axis y as tangent and axis z as normal to the surface plane). OnCheck mark means that the twist is free and the cut size is not transferred. EsYou can also enter the constant of a torsion spring.There is already an interesting technical article on the subject of line joints on our website .
AnswerLine joint:Line joints control the connections between surfaces. Thus, complete decoupling of surfaces or yielding couplings via linear springs can be considered.
The line joint functions to reduce the stiffness in the adjacent first row of elements of the associated surface according to the degrees of freedom chosen. In concrete construction can with a line joint z. B. an assembly joint can be defined. In timber construction, modeling with line hinges is necessary due to the very limited rotation transmission of forces.Line release:With line sharing, elements connected to a line (bars, areas, and volumes) can be decoupled from each other. A new line will be generated in the same place, transmitting only the locked degrees of freedom. In contrast, non-linear effects can be taken into account for a line joint (see Figure 2).First, the line release type must be created. This defines the open degrees of freedom or spring constant and optionally nonlinearities. Subsequently, the line release for bars, areas and volumes can be made on individual lines. The axis system of the release can also be manipulated in the same dialog box.If line joints have already been used in a position, they can be quickly converted to a line release (see Figure 3). This makes it very easy to consider nonlinear effects in the system.
AnswerThe area on the right in Fig. 1 therefore receives a moment in the area of the support because this surface is rigidly connected to the support (the surface itself does not have a line joint). If one wants to exclude this moment, one would therefore have to create an additional line joint for the right-hand surface or provide the support with a rod end joint.
AnswerIn RSTAB there is also the possibility to determine plastic internal forces. To do this, one must select a plastic joint as non-linearity via the rod properties (see Figure 1). However, this does not involve interaction of the plastic forces. Another possibility is to directly set joints with nonlinear properties. However, with this method you have to estimate in advance where these joints form.In RFEM it is possible to select a corresponding material model (see Figure 2).
AnswerTo perform a design for several connection nodes, the following points must match:
Deviations in the connection nodes may be as follows:
- the different connection nodes must use the same geometry type, for example, the knee crack
- The beam and the column (s) of the different connection nodes must be the same length
- the material of the column cross-sections and the cross-section material must match respectively
- The horizontal beam and the column (s) of the different connection nodes must have the same cross-sections
- Beams of different connection nodes must have the same inclination
- You can use different cross-section and material numbers
- the number of connected elements, such as tension diagonals, may deviate
- Different types of hinges can be used
AnswerThe auxiliary values λ1 and λ2 are required to determine the effective lengths.
These two values are used to determine an α value from Figure 6.19 of EN 1993-1-8, which is then used to calculate the effective lengths (for non-circular flow lines) of the T-stub flanges.
The maximum value for λ1 is 0.9 and the maximum value for λ2 is 1.4 -> see Figure 6.11 of EN 1993-1-8
Based on your geometry, however, the result is, for example, a λ2 of> 1.4 for the end plate
α can only be calculated with the maximum value of 1.4.
The easiest way to find the internal forces at these nodes is to print the pictures of members into the printout report.
If this solution is not an option, you can also find the values in the result table 4.1 in the printout report. Since the extreme values are only activated by default, it is still necessary to activate nodal values in the selection.
It is usually not reasonable to include the internal forces of all member in the printout report. Therefore, you can only select the members that are relevant to you.
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