#### Further Information

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• ### I have set a variable load distribution for a generated load. This should be applied incrementally in a certain direction. However, the load is not stepped, but is displayed with a linear distribution. How can I display the load correctly?

New

FAQ 004344 EN

In order to display the loads correctly, it is necessary to make some adjustments. In the case of an incrementally applied load, the boundary of the area load plane may only be defined in sections (by load increment). Otherwise, the load is distributed linearly over the entire area load plane.
• ### How can I set as quickly as possible that the load combinations generated by the program will be calculated according to the geometrically linear analysis, for example?

New

FAQ 004331 EN

In the "Edit Load Cases and Combinations" dialog box, you can specify in the bottom right of the "Combination Expressions" tab which method of analysis should be used as the basis for the generated load combinations. By default, the linear calculation according to the geometrically linear analysis is preset for load cases and the nonlinear calculation according to the second-order analysis for load combinations.

Thus, you can quickly determine whether the load case or the load combination is calculated according to the geometrically linear, second-order, or large deformation analysis. The postcritical analysis option allows you to carry out the stability analysis according to the large deformation analysis with regard to the post-critical failure of the entire structure.

In case the model includes cable members, the calculation according to the large deformation analysis is preset in all cases.
• ### When running PLATE‑BUCKLING as a stand‑alone program or as an add‑on module within RFEM/RSTAB, the "from RFEM" or "from RSTAB" button is grayed out.

If the PLATE‑BUCKLING add-on module is not opened as a stand-alone version, but via RFEM or RSTAB, it is possible to import the panels (c/t parts of a member cross-section) and the respective load cases of the RFEM or RSTAB model to PLATE‑BUCKLING (see the figure).

If there are no valid cross-sections of PLATE‑BUCKLING found in the model file of RFEM/RSTAB, the option for importing the buckling panels remains inactive.
• ### Is it possible to design tapered members or trapezoidal panels with the FE-BEUL add-on module?

With the PLATE-BUCKLING add-on module, you can only calculate rectangular buckling panels.

The panel is entered via 1.1 of the add-on module. Alternatively, the panel can also be created from an existing RFEM or RSTAB file by selecting the respective c/t-part.
• ### What happens if I activate the "Soil failure" function in RF-SOILIN?

The zero coefficient of structural soil strength can be used for better convergence of deeper excavations or small loading. Damaged soil have no structural soil strength. Therefore, it better picture damaged subsoil in the upper layers with this function. The possible entry for the depth of the soil failure is from 0.0 m to 1.0 m.
• ### For some reason, the prestresses are no longer displayed graphically for me. How can I display it again?

FAQ 004173 EN

Mostly, it is in this case so that the 'Action Category - Prestress' in the 'Project Navigator - Display' is hidden.  All loads contained in a load case with the action category ‘Prestress’ are no longer displayed in this case. When activating the function, the loads should be displayed as usual.
• ### When calculating a connection with the FRAME-JOINT Pro add-on module, a note appears indicating that the value is outside the allowable range (existing value: 108, minimum value 100, maximum value 100). What does the mentioned note mean?

The 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).
• ### How do I determine the effective lengths of frame columns in RFEM or RSTAB?

FAQ 003538 EN

The easiest way to do this is to use the add-on modules RSBUCK (RSTAB) or RF-STABILITY (RFEM).

RSBUCK and RF-STABILITY perform an eigenvalue analysis for the entire model with a certain state of normal force. The axial forces are increased iteratively until the critical load case is reached. This stability load is characterized in the numerical calculation by the determinant of the stiffness matrix becoming zero.

If the critical load factor is known, the buckling load and the buckling curve are determined from this. The effective lengths and effective length factors are then determined for this lowest buckling load.

The result shows, depending on the required number of eigenvalues, the critical load factors with the corresponding buckling curves and for each member - according to its mode shape - effective length about the strong and the minor axis.

Since usually, every load case has a different normal force state in the elements, a separate corresponding effective length result for the frame column arise for each load situation. The effective length whose buckling mode causes the column to buckle in the corresponding plane is the correct length for designing the respective load situation.

Since this result may be different for each analysis due to the different load situations, the longest effective length of all calculated analyzes - equal for all load situations - is assumed for designing on the safe side.

###### Example for manual calculation and RSBUCK/RF-STABILITY
There is a 2D frame with a width of 12 m, a height of 7.5 m and pinned supports. The column cross-sections correspond to I240 and the frame beam to IPE 270. The columns are loaded with two different concentrated loads.

l = 12 m
h = 7.5 m
E = 21000 kN/cm²
Iy,R = 5790 cm4
Iy,S = 4250 cm4

NL = 75 kN
NR = 50 kN

$EI_R=E\ast Iy_R=12159\;kNm^2$
$EI_S=E\ast Iy_S=8925\;kNm^2$

$\nu=\frac2{{\displaystyle\frac{l\ast EI_S}{h\ast EI_R}}+2}=0.63$

This results in the following critical load factor:

$\eta_{Ki}=\frac{6\ast\nu}{(0.216\ast\nu^2+1)\ast(N_L+N_R)}\ast\frac{EI_S}{h^2}=4.4194$

The effective lengths of the frame columns can be determined as follows:

$sk_L=\pi\ast\sqrt{\frac{EI_S}{\eta_{Ki}\ast N_L}}=16.302\;m$

$sk_R=\pi\ast\sqrt{\frac{EI_S}{\eta_{Ki}\ast N_R}}=19.966\;m$

The results from the manual calculation correspond very well with those from RSBUCK or RF-STABILITY.

###### RSBUCK
$\eta_{Ki}=4.408$
$sk_L=16.322\;m$
$sk_R=19.991\;m$

###### RF-STABILITY
$\eta_{Ki}=4.408$
$sk_L=16.324\;m$
$sk_R=19.993\;m$
• ### How many divisions must a member have for the calculation in RFEM so that I get accurate results?

FAQ 003485 EN

It is not possible to globally answer this question because it depends on the system. There are several divisions to be considered in RFEM.

###### 1. Member divisions for results tables
You can create member divisions for result values by using the menu 'Insert > Model Data > 'Member Divisions'. This division ensures that - e.g. in the RFEM results tables - the internal forces of members can also be displayed at intermediate points. The graphical output remains unaffected.

###### 2. Member divisions
The divisions for the graphical result diagram and the determination of the extreme value can be viewed and influenced in the FE mesh settings (see Figure 1).

For cable, foundation, and tapered members or members with plastic properties, you can specify the number of internal divisions. They lead to a real division of the member by intermediate nodes. However, if a member is arranged on the boundary line of a surface or if the definition line has an FE mesh refinement, the specification has no effect.

Select the 'Activate Internal Member Divisions for Large Deformation Analysis' option to divide also beams by intermediate nodes for the calculation according to large deformation analysis so that these members are calculated with higher accuracy. The number of member divisions is taken over into the input field above.

If using the division even for straight members, which are not integrated into surfaces, FE nodes are generated on all free members and considered for calculations according to the linear static and second-order analysis. The length of the finite elements is either determined by the global target length l FE set in the General dialog section or entered manually.

With the option 'Use Division for Members with Nodes Lying on Them', RFEM generates FE nodes on those locations of the member where end nodes of other members are lying, without having any connection existing between these members.
• ### I use the load generator 'Convert Area Loads to Member Loads via Cells'. What is the function of the 'Nodes on Virtual Lines' function?

FAQ 003431 EN

If a cell closed on all sides is detected in the structural model, it can be used for the load application. However, if the desired load range is not completely enclosed by members, the cell is not recognized by the load generator.

With the 'Nodes on Virtual Lines' function, you can define the corner nodes of the load area manually and thus clearly define the cell area. The cell defined in this way can then be selected as usual by using the pick function of the individual cell nodes.

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

#### 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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