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• ### Why do the results of a combination of load cases differ from the EK formed from load combinations?

New FAQ 002888 EN General RFEM RSTAB

When creating a load combination, the calculation type "II. Order "default. For linear systems, however, which are statically indeterminate, the results for load cases, which are calculated by theory according to the first order, can therefore differ.
• ### I would like a stair railing, for which I have created a set of rods, measured. The profile is a hollow profile. Can the proof of stability of the whole system be made for this purpose, or do I have to transfer this to all stock in STAHL EC3 in a replacement bill?

For 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.
• ### When using plastic material according to the second-order or large deformation analysis III. Expect Order?

FAQ 002615 EN General RFEM

No, when using a nonlinear material model, it is not absolutely necessary to determine according to Theorie II. Or III. To calculate order. The material nonlinearity is also considered in the calculation according to the linear static analysis.

The calculation according to Theorie II. Or III. Order means that the equilibrium is set on the deformed system. Thus, it is a geometric nonlinearity.

Difference between II. And III. Order is that at III. Also large rotations may occur.

Thus, if there is no stability problem or the stability problem is analyzed in another way, the calculation according to the linear deformation analysis is sufficient.

• ### What is the difference between RF- / FE-LTB and RF- / STEEL Warping Torsion? Both expect the 7th Degree of freedom.

That's right, both add-on modules count on the 7th. Degree of freedom, warping.

The difference is that in RF- / FE-LTB, only the loads acting directly on the set of members are automatically detected. Loads from other structural components that are indirectly effective on the set of the RFEM implementations must be added manually as Extra Loads. In RF- / FE-LTB, a complete recalculation of the structure takes place.

RF- / STEEL Warping Torsion on the other hand analyzes the internal force diagrams from the calculation of the main program and then calculates the loads back. They will be newly applied and calculated. Thus, the input of the loading is omitted, which means a time saving.