In the Knowledge Base, you’ll find technical articles and tips & tricks that may help you with your design using Dlubal Software.
Frequently Asked Questions (FAQ)
Using the Results navigator, it is possible to show the resultant of all support forces and their components.Is it also possible in RFEM to show the resultant support force of a single surface with foundation?
FAQ 002368 EN Results RFEM
AnswerYes, support forces of single surfaces can be displayed in the table "4.21 Surfaces - Contact Stresses" available in the RFEM table window. This table can be opened by right-clicking one of the tabs of the "4.xx - Results" table (see Figure 1). In addition to the contact stresses, you can also see the corresponding support forces (see Figure 2).
FAQ 002358 EN Results RFEM
AnswerTo define an average region on curved surfaces, the projection direction has to be clearly defined. Since this is not possible for the "Perpendicular" option, you can define the direction yourself. Either along the global axes X, Y, and Z, or with a vector.
How can I define which internal forces and deformations are displayed by default in the result diagrams?
FAQ 002310 EN Results RSTAB RFEM
First, open the result diagram of a member, line support, section or line. Then select the desired internal forces and deformations.
Finally, right-click the navigator and select Save Check Boxes State.
Use Refresh Check Boxes State (this button is now available) to cancel your settings.
I get internal forces which I didn't expect because they don't correspond to the release definitions. What could be the reason?
FAQ 002267 EN Results RFEM RSTAB
In the calculation parameters of RFEM and RSTAB, you find the option “Refer internal forces to deformed structure” for each load combination and each load case. The calculation according to the second-order analysis is required here.
We explain the relevance with a simple example of a loaded cantilever (see figure). The load of the cantilever results in a little rotation at node 3. If you perform the calculation according to the second-order analysis, you decide with this option if the internal forces on this node refer to the original or to the rotated coordinate system. If the structure is intiially calculated according to the linear static analysis, this results in the following internal forces (RO 101.6×3.6, S235):
Nx = 0
Vy = 0
Vz = 3,00 kN
Mx = 0
My = 9,00 kNm
Mz = 0
The forces and moments can be understood as vectors (Equation 1 and Equation 2). At node 3, a rotation results according to Equation 3.
Thus, the local member axes system is rotated by the angle φy. Now, the internal forces are converted to the rotated coordinate system. This is done by multiplying the vector by the so-called rotation matrix (http://en.wikipedia.org/wiki/Rotation_matrix). The rotation matrix for the rotation about the y-axis is shown in Equation 4. The conversion is carried out by Equation 5 and 6. Inserting the numbers results in Equation 7.
It becomes apparent that a
littlepart of the shear force turns to a tension force:
Nx = 0,4326 kN
Vy = 0
Vz = 2,969 kN
The moment vector remains unchanged.
You can check the calculation for this simple case as shown in Equation 8.
It is now clarified which effect must be selected for this field in the calculation options. However, what are the “correct” internal forces? In most cases, they are the internal forces which are more accurate. A precondition for the calculation according to the second-order analysis is small rotations. Thus, the results must not differ significantly. However, if this is the case, you have to perform the large deformation analysis. Large deformations are allowed here and results always refer to the rotated coordinate system. For calculations according to the linear static analysis, internal forces always refer to the original coordinate system.
FAQ 002110 EN Results RFEM RSTAB 5.xx 8.xx
AnswerRFEM and RSTAB calculate a reduced moment of inertia ly according to the article "Design of Castellated Beams" by Rolf Kindmann, H. J. Nieburh, H. Schweppe.
The reduced moment of inertia ly, for example for WAB HEB 340‑340, is calculated as follows:
red ly = 0.8 * A * ((H - tg) / 2)2
red ly = 0.8 * 150.50 * ((51.00 - 2.15) / 2)2 = 71.828 cm4
For design of connections, I want to display internal forces at the start and and nodes of a beam in a result table. However, the beam consists of several members, which causes very unclear tabular representation. How can I optimize this?
FAQ 002083 EN Results RFEM RSTAB 5.xx 8.xx
AnswerIn this case, the best solution is to create a set of members from the individual members of a beam. Result tables provide an option (after the calculation) to display the internal forces related to sets of members. Use the result filter function to display node results. In this way, you can see the required internal forces for each start and end node. For a documentation, you can export these tables to Excel and adapt them, if necessary.
This warning points out, that the web thickness in the curtailed beam is smaller than the upper web of the cross-section. Web thicknesses of curtailed cross-sections have to be at least equal.
When analyzing a member in RF-/STEEL EC3, the result windows show a difference between the moments listed in design internal forces and the moments used in the design. What has caused this difference?
FAQ 002042 EN Results RF-STEEL EC3 STEEL EC3 5.xx 8.xx
If this difference appears in the design Bending and Compression according to 6.3.3., you can find the explanation in Eurocode 1993-1-1, Cl. 6.3.3. (4). In the explanation of variables, there is written: "the design values of the compression force and the maximum moments". The word "maximum" should be emphasized here. Therefore, the results display the corresponding axial force in the case of design by x‑locations. However, this force applies the maximal moments on the member or set of members.
FAQ 002036 EN Results RFEM RSTAB 5.xx 8.xx
You can change the printout report header in a 3D PDF by adjusting the header of the normal printout report. The new printout report header is then applied also for the 3D PDF.
FAQ 002033 EN Results TIMBER Pro RF-TIMBER Pro 5.xx 8.xx
Yes, it is possible. For reasonable predimensioning of cross-sections in RF‑/TIMBER Pro, you can optimize any cross-section of the relevant cross-section serie.
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