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Frequently Asked Questions (FAQ)
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AnswerFor a vault-free cross-section, a proof of the complete system is recommended using theory II. Order - internal forces and local imperfections. The entry of the effective lengths and nodal bearings (with staff sets) can thus be omitted. However, please activate gamma_M1 for cross-section verification.
AnswerIndependent submodels are not interconnected and are considered as separate submodels in the calculation. They are thus independent models without influencing each other (see Figure 2).It is recommended to edit submodels separately as individual files. Then a stability analysis with RSKNICK is possible.Otherwise, the partial models must be connected to each other. In this case, it should be taken into consideration that the static systems of the submodels should be retained when the submodels merge into an overall model (see Figure 3).The feature "Independent Systems" is helpful in detecting partial models. This finds all independent systems and lists them as groups (see Figure 4).One finds this function under Extras -> Model control -> Independent systems.
AnswerThe dimensioning of cold - formed, thin - walled components and sheets is possible as a finite element calculation with the following programs. Basic program RFEM + RF-Stable (determination of the branching figure) + RF-IMP (generation of the pre-deformed FE mesh for the proof of stability) + RF-STAHL surfaces (calculation of the second-order theory determined stresses on the pre-formed model).
The proof of stability for tensile structures can be converted into a pure stress analysis, if the theory is considered to be 2-fold and the imperfection required by the standard has been applied to the system.
With the help of the modules RF-STABIL and RF-IMP imperfection (resp. a preformed FE mesh). The type of imperfection depends heavily on the component and the standard used. For bars, which were modeled as a tensile structure, the values from DIN EN 1993-1-1: 2005 5.3 can be used. For flat surfaces, for example, the values from DIN EN 1993-1-5: 2006 Appendix C can be used. For trays, the problem is much more complex and there are different approaches. From a generation of imperfections I would advise against this and perform the buckle proof by means of MNA / LBA concept according to DIN EN 1993-1-6, which does not require an approach of imperfection.
If, for example, the surface model of a steel girder is to be detected, you can proceed as follows, for example:
First A burden me comparatively (compared to. other internal forces in the load case) select high normal forces, in most cases the self-weight load case or a load case combination with the corresponding own weight is suitable. It may be necessary to provide each load combination with an individual imperfection.
2. Calculate load combination according to 1-order theory and use as the basis for RF-STABIL
3. Using RF-STABILITY to find the first eigenstate of a global failure
4. Using RF-IMP, use the calculated eigenmode as the basis for an imperfection. In this case, for example, 1/300 of the carrier length can be used as the amplitude.
5. Create a load case combination that uses the generated imperfection as a basis and is calculated according to 2-order theory.
6. Perform a proof of tension on the basis of this load case combination, which at the same time is also proof of stability of the structure.
AnswerYou can change the profile, generally adapt the model and its loads, or enable stabilization in STEEL EC3.In particular, the settings for latitudinal bedding and shear field in the mask 1.12 Bar parameters or 1.13 Bar set parameters, which are then taken into account in the module-internal eigenvalue solver for determining the branch load, are suitable for this purpose.
Please check the boundary conditions, that is, the definition of the nodal supports, and in particular the application of the imperfection in window 1.13 "Parameters - Sets of members". The imperfection is preset as L / 150, which may represent a conservative solution.
It is not possible to display support forces. However, you can perform a design with RF- / FE-LTB: It contains the output of support forces.
As the procedure according to 6.3.3 EN 1993-1-1 can only be applied for components with bending and compression for doubly symmetrical cross-sections, the add-on module complies with the general method according to 6.3.4 EN 1993-1-1. This method is applicable for arbitrarily single-symmetric cross-sections. In Germany, however, only I-sections are permitted, which is why the warning appears here.
You can perform a stability analysis according to the second-order analysis as a cross-section design, which is possible with the add-on modules RF- / FE-LTB or RF- / STEEL Warping Torsion.
Alternatively, you can also allow the general approach for non-I cross-sections in the "National Annex" dialog box, but you deviate from the National Annex.
The reason for this warning is that unsymmetric cross-sections can not be designed according to the methods mentioned in 6.3.3 EN 1993-1 or the general method according to 6.3.4 EN 1993-1-1.
You can perform a stability analysis according to the second-order analysis as a cross-section design, which is possible with the add-on modules FE-LTB or STEEL Warping Torsion.
AnswerPlease check whether you have selected sets of members for the design in General Data: The module extension RF-/STEEL Warping Torsion is only possible to use for the set of members design, not for members.
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