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Frequently Asked Questions (FAQ)
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In RFEM and RSTAB, the simplified design from , Chapter 2.2.3, have been implemented for the automatic load combinations. This means that strictly speaking, only structures concerning the final deformation may be analyzed, in which materials with identical creep behavior occur since the creep deformations are considered in a simplified way on the load side. If the structure is a mixed structure made of wood with different creep properties or in combination with steel, the final deformations must be determined according to  Amendment to 2.2.3 as follows:
'(4) If a structure consists of structural components or components with different creep properties, the long-term deformations should be calculated according to 188.8.131.52 (1) due to the quasi-permanent combination of actions with the final values of the mean values of the corresponding elasticity, shear, and displacement modules. The final deformation ufin is then calculated by superposition of the initial deformation due to the difference of the characteristic and quasi-permanent combinations of actions with the long-term deformation.'
However, this requires a superposition of results from different load combinations, which cannot be implemented automatically in RFEM and RSTAB.If the different creep properties are to be taken into account, the load combinations must be created manually, and the stiffness must be reduced according to the creep coefficient.The procedure is described using the example of a timber-concrete composite floor presented on the Info Day 2017. Below this FAQ, you can find the link for this.
AnswerTo display the isosurfaces of the results in monochrome, you have to edit the color scale. To do this, simply double-click the color scale or edit the color scale with the right mouse button (see Figure 01). The slider can then be pushed down so far that only one color remains. This can be changed by double-clicking the color. Then, the maximum value can be transferred manually to the penultimate input field (see Figure 02). If you want a colorless display, define a very small number for the penultimate value. It is also recommended to activate the ‘Outlines of Deformed Surfaces’ option (see Fig. 03).
AnswerThe increase of the crack factor kcr still has to be done manually because the program does not know where the end of the grain is defined. To do this, divide the member by 1.5 m from the end of the grain so that the affected areas can be designed as a separate member (see Figure 01).Two design cases are now required (File → New Case ...). In case 1, members within the 1.5 m are selected for the design. In case 2, it is necessary to select the members where the 30% needs to be considered. Then, in case 2, the kcr value is adjusted manually in the settings for the National Annex. Thus, a kcr of 0.65 results for C24, which is entered as shown in Figure 02. The design is carried out this way with an increased kcr value.
AnswerIn this case, it is recommended to use the module extension RF-/STEEL Warping Torsion :RF-/STEEL Warping Torsion is an extension of the RF-/STEEL EC3 and RF-/STEEL AISC add-on modules. It performs flexural-torsional buckling analyzes of members according to the second-order analysis with seven degrees of freedom and a form of imperfection affecting the mode shape.You can find more information in the links below this FAQ.
AnswerTo consider average regions when designing in RF-LAMINATE, they must always be activated in the detail settings of the add-on module. See Figure 01 with the detailed settings in RF-LAMINATE for this.
The definition of surface supports should be as realistic as possible. Experience shows that the equation solver works most effectively with this. To simplify matters, degrees of freedom are often defined as 'fixed'. However, this can have a big impact on the overall stiffness matrix and cause numerical problems (see Figure 01).
It is better to work with springs in order to avoid the numerical problems. It is often sufficient to define very stiff springs (see Figure 02). The same applies to the foundation perpendicular to the surface. You can find more information in  and in the links below this FAQ.
To do this, select the checkbox in Table 1.2 Geometry in column J (see Figure 01).Then, it is possible to view the release definitions in the 'Releases' tab (see Figure 02).If you want to modify the releases, you have to set the support type to 'User-Defined' in the 'Support' tab. The releases can then be freely defined (see Figure 03).
There is no load distribution displayed between the external facade elements at the example shown in Figure 01. Unstressed cells are not displayed according to the color scale during load distribution, but remain empty. Thus, the value on these elements is 0. This has the advantage that it is recognized immediately that the FE elements are not stressed.The cause of the problem can be visualized directly in RWIND Simulation. By default, calculations are based on a simplified model. Depending on the setting, the shell of the model can be refined or coarsened. An FE mesh is placed over the structure, so to speak, and depending on the level of detail, this FE mesh clings to the model. Figure 02 shows the extent of the level of detail that is too small. The surfaces standing on the façade are not displayed well enough and no wind flows between the cantilevered surfaces in the simulation, which is why these internal surfaces do not experience any wind pressure.The level of detail can be adjusted in RWIND Simulation by 'Edit Model' or directly in RFEM in the settings for the wind load simulation (see Figure 03). Optionally, the simplified model can also be completely deactivated in RWIND Simulation.In the case of a greater level of detail (corresponds to a finer FE mesh), the cantilevered surfaces are displayed cleanly and the FE elements are stressed accordingly (see Figure 04 and Figure 05).
The system shown in Figure 01 is loaded with the load generator.
The result is demonstrated in Figure 02. Due to the different member lengths, the two beams do not result in the same load magnitudes. Figure 02 also shows the graphical load distribution. The rectangular connection of the members to the bisector is considered the load application length. This corresponds exactly in both cases.
Figure 03 also shows a check by means of a surface system. These, too, are consistent with the member model.
The stiffness modifications can be controlled separately for the following elements:
The first option 'Materials' is only activated for load combinations by default (see Figure 02) because the second-order analysis is preset for this. When the function is activated, the stiffness of all elements is reduced by the partial safety factor of the material (see Figure 03). This is especially important for timber construction in Europe. If the automatic load combination was selected for the standard EN 1990 + EN 1995, SIA 260 + SIA 265 or DIN 1055-100 + DIN 18008, the default settings are different. Provided that the partial safety factor of the material is defined as 1.0, it does not matter if the function is activated or not.
Use this option to control the multiplication factors of individual cross-sections. In the 'Modify' tab of the 'Edit Cross-Section' dialog box, it is possible to adjust the moments of inertia as well as cross-section surfaces. This affects the stiffness of the cross-sections.
When editing a member, the 'Modify Stiffness' dialog tab is available. There are various definition types (see Figure 05). The "Multiplication Factors" option allows you to modify the stiffness of individual members in analogy to the cross-sections.
For surfaces referred to as 'Standard' and 'Without Tension', the stiffness of the surface can be adjusted in the 'Modify Stiffness' tab of the 'Edit Surface' dialog box. There, it is possible to modify the stiffness matrix elements by a factor (as with orthotropic surfaces).
Further options for stiffness modification
Additionally, a further option can be selected in the calculation parameters to adjust specifically stiffness of other elements (see Figure 07). When selecting the 'Modify stiffness' option, a new tab opens (see Figure 08). In addition to the member and surface stiffnesses, it is also possible to adjust the stiffnesses of supports and hinges individually.
Interactions of individual factors
If several factors have been defined for an element (e.g. cross-section and member), they are multiplied by each other. For the example shown in Figure 09:
Global control of stiffness modification
In the global calculation parameters (see Figure 10), it is possible to deactivate all options mentioned above at once. The local settings in the calculation parameters of the load cases or the load combinations are ignored.
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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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