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Frequently Asked Questions (FAQ)
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AnswerThis is caused by the active partial safety factor γM. After you deactivate it, the results are identical.
The shear stiffness was probably not considered in the manual calculation or it was assumed as infinite. In RFEM/RSTAB, this is taken into account according to reality by default, so that the deformation is more unfavorable than in the manual calculation, which only includes the deformation component from bending.
The shear stiffness can be deactivated under the global calculation parameters (menu "Calculation" → "Calculation Parameters"), see the figure.
The reference system can be changed both in the graphical display in the Project Navigator (see Figure 01) or in the tabular results in the add-on module (Figure 02).
Figure 03 shows the different deformations of a structural system. On both sides, Construction Stages 2 to 4 are displayed from top to bottom, referring to the undeformed system (initial state) on the left and to the respective construction stage on the right.
AnswerWhen calculating according to Theory III. Order, the membrane stiffness or the axial stiffness is also considered with regard to pure bending stress. For theory I and II. Order, only the bending stiffness is taken into account for pure bending stress.
Open SHAPE-THIN as an administrator: Right-click the SHAPE‑THIN instance → "Run as Administrator", see the figure.
As an alternative, you can uninstall SHAPE‑THIN and perform a new installation as an administrator as described above.
AnswerWhen defining an imperfection, there are four options available for activating the precamber.
The attached example video shows that the limit slenderness is not exceeded for the middle column. No imperfection is applied. The bending moment Mz is zero.
The precamber is always taken into account.
- EN 1993-1-1 (5.8)
The precamber is only taken into account if the slenderness ratio is greater than in Formula (5.8) of the standard EN 1993‑1‑1 (see Figure 01).
- DIN 18800 (207)
For the calculations of existing buildings, this option according to the withdrawn standard DIN 18800 was left in the program.
Here, you can specify a value for the member coefficient ε0. The member coefficient is determined according to the formula in Figure 02.
In RF‑CONCRETE Members, the deformation in the cracked state is determined by using a coefficient "ζ" (according to EN 1992‑1‑1, 7.4.3). For this simplified method, the coefficient ζ is only determined once per member. The linear deformation is upscaled according to the governing location in the member.
In this context, it is possible to determine different coefficients ζ for the individual members. When scaling the linear deformation, jumps occur between the individual members.
To avoid this effect, it is recommended to use sets of members.
First, check if the "design of deformation" has been activated in the settings for the calculation of the SLS designs.
Furthermore, check whether a load for the "quasi-permanent" design situation has been specified in the "Serviceability" tab of Window 1.1. By default, the calculation of deformations in RF‑CONCRETE Surfaces (with RF‑CONCRETE Deflect or RF‑CONCRETE NL) requires a quasi-permanent load.
AnswerThe instability appearing in newer versions of the program is caused by a change in the setting of the initial stiffness that we had to do. This can be corrected in Calculation Parameters, under the Form-Finding tab. You use a lower FF calculation speed, which will not reduce the initial stiffness so radically, and the calculation will be more stable. In some cases, the number of FF iterations still needs to be increased.
In principle, the calculation with RF‑FORM‑FINDING has the same requirements as the calculation without this add-on module, so the criteria for general instabilities should be checked (see Links).
However, problems often occur with RF‑FORM‑FINDING because the form-finding process has been activated for too many elements. Therefore, you should check whether the correct (necessary) elements have been activated (see Figure 01).
In the following example in Figure 02, the form-finding has been activated for all horizontal members. This results in the error "The stiffness matrix is singular!" (see Figure 03). If you deactivate the beam members, the calculation is successful (see Figure 04).
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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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