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Frequently Asked Questions (FAQ)
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AnswerThe DUENQ cross-section consists of several non-contiguous partial cross-sections, so that in DUENQ it is calculated according to the theory of stiffening systems. DUENQ also gives a hint before the calculation. The dimensioning of such cross sections is not possible in add-on modules such as RF / STEEL EC3, RF / ALUMINUM etc.In most cases, however, the cross-sectional parts should be connected to each other. The FAQ describes how this connection can be modeled.
RF-/LTB requires clear internal forces along the member axis for the design. This condition exists due to various standard requirements that regard the member element to be designed as a structural component and use result gradients along the member axis to determine design parameters (normal force diagrams, bending moment diagrams, etc.).
To meet this requirement, the internal forces to be designed must project clear design cases for the calculation core. Representatives of such unique design cases are load cases and load combinations. Since result combinations are usually used for enveloping results, they are locked in RF-/LTB.
For the calculation of cantilevers, the determination of the ideal elastic critical moment Mcr is crucial. This can be determined for singly symmetric I-sections applying "Lohse" (LTB manual, Chapter 3.4.4). However, rotational restraints and lateral restraints are not taken into account.
The calculation of M Ki is based on the same formulas. Nevertheless, there is one big difference:
DIN 18800-2 simplifies the coefficient of the load application point C 2 and sets it to 0.5. Eurocode 3 captures this factor more precisely. Depending on the load, C 2 can be between 0.41 and 1.562.
If the load application point is set in the center of gravity (assuming double-symmetrical profile), identical M Ki values result according to DIN 18800 and EC 3.
The coefficient ζ for the consideration of the pressure force distribution in the flange is a correction factor to determine the critical buckling moment Mcr for certain boundary conditions and loads.
In RF-/LTB, this correction factor ζ always refers to the largest bending moment of the equivalent member. The literature references often give the coefficient ζ in relation to the center of the equivalent member (see also RF-/LTB Manual).
However, the RF-/LTB also provides an option to define the zeta-coefficient manually. For this, select the option 'Assign LC/CO Individually' in chapter Method of Determining Mcr (see Figure).
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Wind Simulation & Wind Load Generation
With the stand -alone program RWIND Simulation, you can simulate wind flows around simple or complex structures 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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