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Answer
Yes, that is possible.
First, RFSTABILITY (or RSBUCK in RSTAB 8) can be used to determine the effective lengths for a particular structure and loading.They can then be imported into RF / TIMBER Pro in the "Effective Lengths" dialog box. 
Answer
When designing general crosssections in the RFSTEEL AISC module, a "Nondesignable" message is given for the design ratio. General crosssections are defined in the program as userdefined sections or shapes which are not included in the specification. Though, some userdefined crosssections can be designed under specific conditions. The warning message is displayed because shear buckling is not provided for general crosssection in the AISC 36016 [1] Chapter G. More info on this topic can be found in the RFSTEEL AISC manual linked below.
This warning can be turned off in RFSTEEL AISC addon module under the "Details" button > Shear Buckling > "Shear buckling warning for general crosssection." 
Answer
Both RFEM and RSTAB present a suitable solution. Numerous European and international standards, as well as various addon modules, are available for both programs, which will facilitate the daily work in steel structures.Basic programs RFEM or RSTAB
The basic programs RFEM or RSTAB define structures, materials, and actions. In addition to creating spatial frame structures, for example, halls, RFEM also provides plate, pane, and shell structures, making it a more diverse option. It pays off if it is necessary to carry out design also in other areas, such as solid construction.Available standards
 EN 199311 (Eurocode 3),
 AISC according to ANSI/AISC 360 (US Standard),
 SIA according to SIA 263:2013 (Swiss Standard),
 IS according to IS 800:2007 (Indian Standard),
 BS according to BS 59501:2000 (British Standard) or BS EN 199311 (British Annex),
 GB according to GB 500172003 (Chinese Standard),
 CSA according to CSA S1609 and CSA S1614 (Canadian Standard),
 AS according to AS 41001998 + Annex 1  1999 (Australian Standard),
 NTCDF according to NTCRCDF (2004) (Mexican Standard),
 SP according to SP 16.13330.2011 (Russian Standard),
 SANS according to SANS 101621:2011 (South African Standard),
 NBR according to ABNT NBR 8800:2008 (Brazilian Standard),
 HK according to the standard for steel structures 2011 (Buildings Department  Hong Kong)
 RF/STEEL  General Stress Designs
Addon modules for structural steelwork
The functionality of the basic programs is supplemented by addon modules. With RF/STEEL EC3, for example, it is possible to perform the design for the structure according to Eurocode 3. The addon module RFSTEEL Warping Torsion supplements this design according to Eurocode 3 with torsional buckling analysis having up to 7 degrees of freedom, provided it doesn´t refer to a standard case of EC3.
Other more specialized applications such as the plastic design, the stability analysis according to the eigenvalue method or the generation of geometric equivalent imperfections and predeformed equivalent models are available. Single modules such as PLATEBUCKLING provide you with support when designing rigid or stiffened plates. With the SHAPETHIN addon module, it is possible to create any thinwalled crosssections. The crosssection properties are determined and stress analyzes or plastic designs can thereby be performed.
The hinged or rigid connections can be designed by means of the RFJOINTS addon modules.
The standalone application CRANWAY is available for the design of craneways.
Dynamic analysisIf earthquake calculations or vibration analyzes are necessary for the building, the RF/DYNAM Pro addon modules provide suitable tools for determining natural frequencies and shapes, analysis of forced vibrations, generation of equivalent loads, or for the nonlinear time history analysis.
In case of having any further questions about the Dlubal software, contact the sales department, please. 
Answer
The setting in Figure 01 only controls the influence on the design side. After having activated this function, the buckling designs in the "Effective Lengths" window are deactivated. Thus, only a lateraltorsional buckling analysis is performed.
Figure 01  Detailed Settings in RF/TIMBER Pro Addon Module
In order to calculate with the design values of the stiffnesses, they have to be reduced by the partial safety factor according to [1]. To do this, select the highlighted option in the calculation parameters (see Figure 02).
Figure 02  Reduction of Stiffness Due to Partial Safety Factor
In case of having used the automatic combinatorics for the standard EN 1990 + EN 1995, this setting is  according to the secondorder analysis  automatically activated for the ULS in respective combinations. This option is automatically deactivated for combinations with SLS as well as for combinations that are generated according to the linear static analysis. However, the automatic assignment is only carried out by means of the analysis type in the 'Combination Expressions' window (see Figure 03).
Figure 03  Calculation Method of Combinations
If you want to calculate the component stiffnesses with the 5% quantile value of the stiffness parameters divided by the partial safety factor, you have to additionally activate the 'Modify Stiffnesses' function in the calculation parameters and modify the stiffnesses manually.

Answer
The easiest way to do this is to use the addon modules RSBUCK (RSTAB) or RFSTABILITY (RFEM).RSBUCK and RFSTABILITY perform an eigenvalue analysis for the entire model with a certain state of normal force. The axial forces are increased iteratively until the critical load case is reached. This stability load is characterized in the numerical calculation by the determinant of the stiffness matrix becoming zero.If the critical load factor is known, the buckling load and the buckling curve are determined from this. The effective lengths and effective length factors are then determined for this lowest buckling load.The result shows, depending on the required number of eigenvalues, the critical load factors with the corresponding buckling curves and for each member  according to its mode shape  effective length about the strong and the minor axis.Since usually, every load case has a different normal force state in the elements, a separate corresponding effective length result for the frame column arise for each load situation. The effective length whose buckling mode causes the column to buckle in the corresponding plane is the correct length for designing the respective load situation.Since this result may be different for each analysis due to the different load situations, the longest effective length of all calculated analyzes  equal for all load situations  is assumed for designing on the safe side.Example for manual calculation and RSBUCK/RFSTABILITY
There is a 2D frame with a width of 12 m, a height of 7.5 m and pinned supports. The column crosssections correspond to I240 and the frame beam to IPE 270. The columns are loaded with two different concentrated loads.l = 12 mh = 7.5 mE = 21000 kN/cm²I_{y,R} = 5790 cm^{4}I_{y,S} = 4250 cm^{4}N_{L} = 75 kNN_{R} = 50 kN$EI_R=E\ast Iy_R=12159\;kNm^2$$EI_S=E\ast Iy_S=8925\;kNm^2$$\nu=\frac2{{\displaystyle\frac{l\ast EI_S}{h\ast EI_R}}+2}=0.63$This results in the following critical load factor:$\eta_{Ki}=\frac{6\ast\nu}{(0.216\ast\nu^2+1)\ast(N_L+N_R)}\ast\frac{EI_S}{h^2}=4.4194$The effective lengths of the frame columns can be determined as follows:$sk_L=\pi\ast\sqrt{\frac{EI_S}{\eta_{Ki}\ast N_L}}=16.302\;m$$sk_R=\pi\ast\sqrt{\frac{EI_S}{\eta_{Ki}\ast N_R}}=19.966\;m$The results from the manual calculation correspond very well with those from RSBUCK or RFSTABILITY.RSBUCK
$\eta_{Ki}=4.408$$sk_L=16.322\;m$$sk_R=19.991\;m$RFSTABILITY
$\eta_{Ki}=4.408$$sk_L=16.324\;m$$sk_R=19.993\;m$ 
Answer
This message indicates that the critical load of the structure or the crosssection has been exceeded.The causes for this are very diverse. Often, insufficient lateral supports have been defined in the STEEL EC3 addon module.It is also possible that the used crosssections or the structure itself cannot be calculated according to the general method in EC3. This FAQ provides information about such a case. 
Answer
The elastic critical buckling load for torsional buckling N_{cr,T} is calculated as follows:
${\mathrm N}_{\mathrm{cr},\mathrm T}\;=\frac1{{\mathrm i}_{\mathrm M}^2}\;\cdot\;\left(\frac{\mathrm\pi^2\;\cdot\;\mathrm E\;\cdot\;{\mathrm I}_{\mathrm w}}{{\mathrm L}_{\mathrm T}^2}\;+\;\mathrm G\;\cdot\;{\mathrm I}_{\mathrm t}\right)$
${\mathrm i}_{\mathrm M}\;=\;\sqrt{{\mathrm i}_{\mathrm u}^2\;+\;{\mathrm i}_{\mathrm v}^2\;+\;{\mathrm u}_{\mathrm M}^2\;+\;{\mathrm v}_{\mathrm M}^2}$
with
E Modulus of elasticity G Shear modulus I_{w} Warping resistance I_{t} Torsion moment of inertia i_{u}, i_{v} Pricipial radius of gyration u_{m}, v_{m} Shear center coordinates in the principal axis system L_{T} Torsional buckling critical length 
Answer
The RFPLATEBUCKLING performs the plate buckling analysis according to Chapter 10 "Reduced Stress Method" of EN 199315. According to EN 199315, 10 (5) a), it is necessary to determine all reduction factors with the modified slenderness ratio of the plate panel ${\overline{\mathrm\lambda}}_{\mathrm p}$ according to Equation (10.2). 
Answer
This function is intended to detect modeling errors in the structure that may lead to instability. Using this method, it is possible to calculate such systems and to determine the cause of the instability graphically.This function is not suitable for the following problems: Calculation aborts due to overloadings (stability problems)
 Determination of buckling curves and buckling modes
If the system is stable and only stability problems occur during the calculation according to the secondorder analysis, all results are set to 0 with this function.The problem solving of instabilities is described in detail in FAQ 2257 . 
Answer
The difference between designing by means of RC and CO consists mainly in the moment distribution applied for the calculation of the ideal lateraltorsional buckling moment Mcr. For a load combination (CO), it is possible to clearly apply the moment distribution for the present load position. For a result combination of the '+' type or an RC that does not correspond to the 'permanent/or' type, however, you can only analyze the enveloping moment distribution. Then, the more unfavorable distribution (Max or Min) is applied. As a consequence, unfavorable values result for the critical load factor.Furthermore, it should be noted when designing according to clause 6.3.3 of EN 199311 that the moment distribution coefficients are set to 1.0 (constant distribution), provided that the moment distribution cannot be determined unambiguously, which may also lead to more conservative results.Summary:
The internal forces applied for the design can be the same in LC and RC, but the moment distribution in the result combination is applied more unfavorably to determine the critical factor. Thus, the RC provides a higher utilization for the design with STEEL EC3.
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