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Frequently Asked Questions (FAQ)
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In RFEM, the interface application 'Simulate and Generate Wind Loads' makes it possible to exchange member, surface, and solid elements, and in RSTAB to exchange the member elements.
To avoid generating a too fine mesh along with a corresponding long calculation time, the program simulates all members with a rectangular cross-section as standard. The size of the rectangular cross-section is selected in such a way that the real cross-section geometry is barely included.
By deactivating the option 'Export Optimized Member Topology', you can avoid this additional optimization of the model and allow consideration of the real cross-section geometry within existing cross-section settings.
If the exact representation of the cross-section geometry requires more than 1000000 elements, the interface automatically changes to the simplified rectangular section display of the cross-sections.
AnswerWith the FE mesh refinement, it is also possible to create an aligned FE mesh in the program. Thus, the automatic FE mesh generator can be controlled to a certain extent. However, it is not possible to use it for setting of a specified mesh geometry.
AnswerThe load from the form-finding load case (FF) is impressed 1.0-fold into the system. If you want to factorize the dead-load in combination with combinatorics, it is possible to additionally create a permanent load case for the dead-load with a load of 0.35 times the load.
AnswerThe cause of such an effect could be free edges, which can deform almost infinitely during Form-Finding. A state of equilibrium is difficult to achieve.As a basis for Form-Finding, there should be no free edges on the membrane surface. Ropes must be arranged on the free edges of the membrane whose stiffness can be based, for example, on the folded or reinforced edge strips of the membrane.
For form-finding, it is primarily important to apply a prestress for the membrane and any provided edge cables. The restraints do not have to be prestressed.
The bracing can be installed as tension members with their initial length (see the figure). As a result of the prestressed membrane and edge cables, the load for bracing is obtained during the calculation.
By activating the RF-/FORM-FINDING add-on module, a high-quality form-finding process is defined according to the URS method before the actual structural analysis for each element with form-finding properties. After the calculation, this process results in an optimal equilibrium shape that approximately corresponds to the specified shape-finding parameters (prestress, sag, etc.).
Since this URS method requires an iterative calculation to display results, the program provides an interactive graphic mode based on the force density method for pure modeling. This mode displays the resulting element shape on the basis of the stored form-finding properties stored when the elements are entered.
To avoid possible initial complications due to incompletely defined models, it is possible to switch the mode on and off at any time in the shortcut menu by using the "Show Shape" option.
During the determination, the graphic mode considers all force-related form-finding entries on member and surface elements. A stable boundary condition in the respective direction is assumed for all relevant nodes with a connected element or support definition. In addition, integrated openings in surfaces are considered for the optimized display of tent points as well.
This interactive form-finding is generally only intended for the graphical display of elements with imposed loading and works independently of the URS form-finding, which is always done before the pure structural analysis. However, the mesh generating for surfaces is based on the currently displayed shape and can thus be influenced by the activation of the interactive form-finding.
AnswerThis message is usually displayed in the case that the member dimensions do not correspond.In the example model, the beam has a flange width of 200 mm and the column support of 160 mm.This joint is not valid in the add-on module as the flange width of the column should be at least as large as the flange width of the structural element to be connected. As soon as the cross-sections are defined according to this rule, the connection design can also be performed.
AnswerNo, the program does not currently provide any wind load generation according to DIN EN 13782. In the "Tools" menu, however, a large number of load generators is available and independent of various standards. You can find an overview of all load generators under the following link.
As the wind load generation is a very complex topic for any model geometries and the standards only display suitable cp values for specific body shapes, the program RWIND Simulation is also available in our product portfolio. This program simulates the wind currents around any building in a numerical wind tunnel and uses them to generate resulting wind loads for the further structural analysis. You can find more information at the following link.
This option performs the design of longitudinal seams of welded cross-sections. Collisions or other connections are not designed. It is important that the thickness of the weld is specified in the cross-section definition (see Figure 1).
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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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