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Frequently Asked Questions (FAQ)
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For the example shown in Figure 01, no load distribution is displayed between the outer facade elements. Unloaded 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, it is possible to refine or coarsen the shell of the model. An FE mesh is placed over the structure, so to speak, and depending on the level of detail, this FE mesh snuggles against the model. Figure 02 shows the extent of the degree 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 degree 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 degree 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).
AnswerThe system shown in Figure 01 is loaded with the load generator. The result is shown in Figure 02. Due to the different member lengths, both members do not result in the same load values. Figure 02 also shows the graphical load distribution. The rectangular connection of the members to the angle bisector must be understood as the load application length. This corresponds exactly in both cases. Figure 03 also shows a check by means of a surface system. Again, they 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 in 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 result is different default settings. If 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 for individual cross-sections. In the "Modify" tab of the "Edit Cross-Section" dialog box, you can adjust the moments of inertia as well as surfaces of the cross-section. This affects the stiffness of the cross-sections.
When editing a member, the "Modify Stiffness" dialog tab is available. There are different definition types (see Figure 05). The "Multiplier factors" option allows you to modify the stiffnesses of individual members in analogy to the cross-sections.
For surfaces of the "Standard" and "Without Tension" type, you can adjust the stiffness of the surface in the "Modify Stiffness" tab of the "Edit Surface" dialog box. There, you can modify the elements of the stiffness matrix with a factor (as with orthotropic surfaces).
Further possibilities of stiffness modification
In addition, you can select another option in the Calculation Parameters to specifically adjust stiffnesses for other elements (see Figure 07). When you select the "Modify stiffnesses" 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.
Interaction of individual factors
If several factors have been defined for an element (for example, cross-section and member), they are multiplied by each other. The result for the example shown in Figure 09 is as follows:
Global control of stiffness modification
In the global calculation parameters (see Figure 10), you can deactivate all options mentioned above at once. The local settings in the calculation parameters of the load cases or of the load combinations are ignored.
AnswerThe function [Generate Loads → From Area Load on Members via Plane...] requires the defined plane to be created from a continuous line. If a curved member is created from arcs, the plane as a polygon cannot find the outer contour of the arc, because it is only an approximation. In short, curved members cannot be loaded by means of the load generator in RFEM.In this case, it is recommended to display the curved member by means of several straight member segments. Thus, the continuous line can be run cleanly. In order to create the corner nodes of the polygon chain more quickly, it is advisable to prepare them e.g. in Excel, depending on the number of member segments. The numbering of nodes is important. The procedure is demonstrated in the video.
Creating the opening by means of an intersectionTo create the opening, you have to create a surface with the diameter of the opening through the pipe wall. With the function 'Create Intersection' single components are created which can be deactivated afterward. The procedure is demonstrated in the video.
Creating the opening by means of a converted intersection lineIt is also possible to convert the found intersection line into a normal line. Then, the intersection can be deleted and an opening can be put into it. The inserted opening must then be manually integrated into the surface (see video). However, it should be noted that the quality of an intersection is higher than the converted intersection line. When using the converted intersection line, discontinuities may occur in the rendering or in the FE mesh, depending on the model.
AnswerIn general, an imperfection describes the Incompleteness of a structure or the deviation from an ideal shape caused by the production. There are different ways to simulate the imperfection. In RSTAB and RFEM, imperfections are represented as equivalent loads. The definition of equivalent loads is shown in Figure 01 and is taken from  . The same is described in EC3  . Since these are equivalent loads that are dependent on the axial force, they are also taken into account for a calculation according to the 1st Order Theory. It is recommended to manage loads and imperfections in separate load cases. They can be combined in an appropriate way with each other in load combinations. Load cases with pure imperfections have to be categorized as action type 'Imperfection' in the general data for load cases (see Figure 02).
If the building envelope is not modeled, the wind load in RWIND Simulation only attacks the surfaces of the members. Elements that would distribute the pressure between them on the members do not exist. In this case, the function "Close Holes" is not suitable for replacing the surfaces. Thus, an automatic transfer of the wind load to RSTAB or RFEM is not possible.
However, you can model the building envelope in RFEM in a separate model and have it analyzed in RWIND Simulation. The wind pressure can then, for. For example, you can create them manually as load with the load generators. The procedure is shown in the video.
AnswerThe same requirements apply for a layered FE mesh as for a contact solid (see the links below this FAQ). If the requirements are not met, the layered FE mesh must be deactivated in the layer layout details (see Figure 02).
AnswerThe surface type 'Trajectory' is suitable for this. Using this option, it is possible to select the path or the guideline and assign a cross-section. The procedure is demonstrated in the video.
AnswerTo be able to consider this non-linearity, it is possible to use the "Partial Activity" function (see Figure 01). This way you can define the limit moment beyond which any other moments will be taken into account.
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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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