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Frequently Asked Questions (FAQ)
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AnswerIn order for smoothing ranges to be considered in the design in RF-STEEL Surfaces, they must always be activated in the detail settings of the add-on module. See Figure 01 with the detail settings in RF-STEEL Surfaces.
The stiffness modifications can be controlled separately for the following elements:
The first option "Materials" is activated only for load combinations by default (see Figure 02), because the second-order analysis is preset here. If this 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 modify the moments of inertia as well as surfaces of the cross-section. This has an influence on the stiffness of the cross-sections.
If you edit a member, the "Modify Stiffness" tab appears. There are different definition types (see Figure 05). The "Multiplier factors" option allows you to modify the stiffnesses of single members in the same way as for the cross-sections.
For surfaces of the "Standard" and "Without Tension" type, you can manipulate the stiffnesses of the surface in the "Modify Stiffness" tab of the "Edit Surface" dialog box. There, as in the case of orthotropic surfaces, you can modify the elements of the stiffness matrix with a factor.
Further possibilities of stiffness modification
In addition, you can select another option in the Calculation Parameters to modify specific stiffnesses for other elements (see Figure 07). When you activate the "Modify Stiffnesses" option, a new tab appears (see Figure 08). In addition to the member and surface stiffnesses, it is also possible to manipulate the stiffnesses of supports and hinges.
Interaction of individual factors
If several factors have been defined for an element (for example, from the cross-section and the member), they are simply 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.
AnswerIn RF-/JOINTS Steel - Rigid, the design according to EN 1993-1-8 Chapter 6.2.7 Equation 6.24 is implemented. If the acting axial force exceeds 5% of the plastic resistance N pl, Rd , Equation 6.24 is used.
Only the default setting of 1 load increment can be set when a complex nonlinear material model is defined. The reason for this is because the program cannot determine the correct material stiffness for each incremental loading amount. The exact maximum load needs to be applied to the structure in order to determine the state of the material's stress/strain diagram.Figure 01 - Material Model - Nonlinear material definedThis setting can be found and changed under "Calculation Parameters" as well as under the "Calculation Parameters" in the load cases and combinations dialog box.
Yes, the AISC module will detect if there are bending or torsional forces on a member and design accordingly per Design Guide 9. The add-on module combines the shear stresses due to bending and axial loads calculated by RFEM and shear stresses calculated using St. Venant's Torsion to make design checks per Design Guide No. 9.The Steel AISC module also has the option under "Details" to activate the RF-STEEL Warping Torsion add-on module extension where a nonlinear warping torsion analysis is performed using 7 degrees of freedom. Normal and shear stresses on the member are independently determined from the AISC Design Guide No. 9. The loading used in this extension is taken directly from RFEM for analysis.
Yes, the RWIND Simulation program is generally designed and can implement any model of RFEM or RSTAB.
Figure 03 - RFEM Model
For a steel structure consisting of pure member elements, the program creates a coherent, voluminous envelope of the member surfaces for the numerical wind tunnel. The result of this modeling for the simulation depends on the available cross-sections and the mesh settings. Due to the wind current, corresponding surface pressures result on this surface layer.
Figure 02 - Surface Pressure on OpenFOAM Mesh
After having calculated the wind flow, the program sums the surface pressures of the member units and returns a corresponding equivalent load (single, uniform, or trapezoidal) for each member axis.
Figure 04 - Options for Member Load Distribution
These loads are applied in RFEM or RSTAB for the further calculation of internal forces.
Figure 05 - Equivalent Load from RWIND Simulation
You can find this setting in the 'Details' of the 'Fire Resistance' tab.You can also control the time of fire resistance individually for each member or set of members.Subsequently, it is possible to find the input in Table 1.10 for the members or 1.11 for the sets of members.
AnswerDuring the development of the FRAME-JOINT Pro add on module, the lower end plate extension was fixed because it results in an improved load transfer of the compressive force into the column.
It is not possible to deactivate the extension and its minimum dimension is defined as follows:
uu = max
- End plate thickness
- √2 * bottom flange weld
- for end plate depths < 200 mm → min 10 mm
- for end plate depths > 200 <400 mm → min 20 mm
- for end plate depths > 400 → min 30 mm
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.
AnswerIn RF-MOVE Surfaces, you can also select a circle as a set of lines. A simple example is demonstrated in the video.
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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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