#### Further Information

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• ### I have created automatic load combinations according to EN 1990 + 1995 (CEN). Although Ψ2,1 = 0, there are the factors greater than zero applied for wind and snow. Is this a program error?

In the case of the combinations according to the general Eurocode without considering a national annex, the design situation in the serviceability limit state - quasi-permanent must be considered as in Figure 01. Here, it becomes clear that due to the last term, the variable loads are considered as unequal to 0 due to Ψ0,i, even in the case of Ψ2,1 = 0.
• ### I use automatic combinations, but some load cases are not used in the generated combinations. How can I change it?

If activating the automatic combinations in General Data, the actions, combination expressions, action combinations, and load or result combinations are created automatically. In this case, some default settings have been selected by the program developers, which apply in most cases.

By default, the following design situations with the respective combination expressions are generated:

• ULS: Ultimate limit state for permanent or temporary situation
• SLS: Serviceability limit state for characteristic situation
• SLS: Serviceability limit state for frequent situation
• SLS: Serviceability limit state for quasi-permanent situation

If load cases of the "Accidental" or "Earthquake" type have been defined, they are not considered in the preset combinations. For these load cases, it is necessary to create a new combination expression manually. You can select the appropriate design situation in the list.

Accidental load cases are only used in the "Ultimate Limit State - Accidental" or "Earthquake" expressions.

• ### Where can I find the information about the preset limit values for a deformation analysis in the STEEL EC3 add-on module?

For building construction, there are no specific limit values specified in the standards for the serviceability limit state design. Therefore, the limit values should be agreed with your client and, if necessary, with the respective authority. Nevertheless, there are various recommendations in technical literature, which we have also adopted as the default values.
• ### I have used the RF‑/DYNAM Pro add-on module to generate the governing result combinations of seismic loads. What is the next procedure to perform the design of the individual structural components?

With the Equivalent Loads and Forced Vibrations add-on modules, you can create the result combinations that contain the governing combinations of seismic loads. To perform the design using them, they have to be combined further on the basis of the accidental combination. This combination is defined, for example, in EN 1990, Section 6.4.3.4:

${\mathrm E}_{\mathrm d}\;=\;\underset{}{\sum_{}^{}\;{\mathrm G}_{\mathrm k,\mathrm j}\;+\;\mathrm P\;+\;{\mathrm A}_{\mathrm{Ed}}\;+\;}\overset{}{\underset{}{\sum{\mathrm\psi}_{2,\mathrm i}\;{\mathrm Q}_{\mathrm k,\mathrm i}}}$

This accidental combination has to be defined manually in RFEM. Make sure that (for a direction combination with the 100/30% rule), both created result combinations from RF‑/DYNAM Pro have to be added with the "OR" condition. Such a combination is displayed in Figure 02.

This accidental combination can then be used for further design. It is possible to evaluate the governing internal forces as well as to import and calculate this combination in the design modules.
• ### Can I create or generate parallel load combinations for the geometrically linear analysis and the second-order analysis (including imperfections) in RFEM?

Yes, it is possible.

If you activate the option to create combinations automatically in RFEM or RSTAB, load combinations for the "ULS" design situation, for example, are set automatically according to the second-order analysis.

In this way, you can obtain a list of load combinations based on the defined load cases, which are calculated according to the second-order analysis. The consideration of imperfection load cases can also be activated.

To generated the load combinations according to the geometrically linear analysis (without imperfections) in addition to the existing load combinations calculated according to the second-order analysis including imperfection, you can create another combination expression for this. In this additional combination, you can select the "ULS" design situation now. However, you can only select the "geometrically linear analysis" as a method of analysis and deselect the imperfection load cases.

As a result, you obtain the load combinations according to the second-order analysis including imperfection (marked in blue in the figure below) and the load combinations according to the geometrically linear analysis without imperfection (marked in red in the figure below).

This approach can be used to perform the stability analysis according to the second-order analysis (including imperfection) on a part of the structure and according to the equivalent member method or model column method on the individual structural components, for example.

Optionally, it is also possible to control the numbering of the individual CO groups in advance in the "Combination Expressions" tab For example, one group can start with CO 100 and the second group with CO 200. In this way, you can achieve a better overview or allocation of the COs.

• ### Why is it not possible to select the individually or simultaneously acting load cases in the "Combination Expressions" tab?

The "Individually/simultaneously acting load cases" option is not available for all standards.

For example, if you select the standard "EN 1990" in General Data of the model, this option is available in the "Combination Expressions" tab.

On the other hand, if you select "ASCE 7‑16", for example, this option is (currently) not available.

• ### How can I consider the partial safety factor γQ,T in the automatic load combinatorics with 1.0 in compliance with DIN EN 1992‑1‑1/NA: Chapter NCI 2.3.1.2 (3) or DIN EN 1990/NA Chapter NDP A.1.3.1 (4)? The value γQ,T = 1.5 is used by default.

To apply this in the program, it is necessary to copy the "Temperature" load case (see Figure 01). All loads contained in the load case will be copied as well. One of the load cases is used for the ultimate limit state (ULS) load combinations, the other one for the serviceability limit state (SLS). The loading in the load case for ULS is now multiplied by 1.0/1.5 = 0.667 (see Figure 02).

In order to ensure that both load cases do not occur simultaneously, but only for the specific design situation, the exceptions are determined in the respective combination expressions. For ULS, it is quite simple to define the dead load case in the way that it is not combined with the temperature load case for SLS (see Figure 03). SLS applies exactly the other way around, that is, the load case of dead load is not combined with the temperature for ULS (see Figure 04). In this case, the "Differently for each combination expression" option must be activated.

The desired load combinatorics is then obtained (see Figure 05).

• ### How can I generate load combinations automatically in an existing file retroactively?

For this, open the "General Data" dialog box of the present model. Right-click the model description in the Data navigator.

As an alternative, you can open the "General Data" dialog box via the "Edit" menu.

In the "General Data" dialog box, you can first select the standard according to which the combinatorics is to be performed, or whether to create load combinations (CO) or result combinations (RC).

If CO or RC are already available in the existing file, a query appears asking whether the program should delete or keep the existing combinations.

• ### What is the meaning of the abbreviations of the design situations in the “Combination Expressions” tab?

ULS: Ultimate Limit State

SLS: Serviceability Limit State

ELS: Proof of Equilibrium Limit State; loss of static equilibrium of the structural system or one of its parts, for example by buckling, buoyancy or lifting

STR: Failure of structural system or its individual parts due to exceeding of material strength, excessive deformations, reaching kinematic state or unstable position

GEO: excessive deformations or failures of soil

• ### When generating wind loads, some external pressure coefficients have a value of 0. What is the reason for this?

For duopitch roofs with a roof inclination of > 5°, the roof areas F, G, H, I and J have to be separately classified according to the windward and leeward side. For the wind direction of 0° (wind in longitudinal direction), positive as well as negative aerodynamic coefficients have to be taken into account for roof inclinations of up to 45°.
For these cases, this results in a total of 4 possible wind combinations, depending on the building side (see Figure 1).
For the direction of flow of 90 ° (wind on the gable side), however, there are no positive external pressure coefficients. Thus, for a building with a roof inclination of 45 °, 10 possible wind load cases would be obtained (0 ° = 4 · 2; 90 ° = 1 · 2).

LC w+:

Only positive (pressure) aerodynamic coefficients per roof area are used.

LC w-:

Only negative (suction) aerodynamic coefficients per roof area are used.

LC w-/+:

Negative (suction) aerodynamic coefficients for the windward side and positive (pressure) coefficients for the leeward side of the roof are used.

LC w+/-:

Positive (pressure) aerodynamic coefficients for the windward side and negative (suction) coefficients for the leeward side of the roof are used.

If there are, for example, only negative coefficients for a load position, then only negative loads are applied to the roof surface. Consequently, there is no pressure -> therefore these values are set to 0. A load case, which thus contains only values with the size 0, could also be deselected during the generation.

For example, this is always possible, as already described, for the LC w + with a wind direction of 90° (gable-sided wind) and a roof inclination of > 15°.

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#### First Steps

We provide hints and tips to help you get started with the main programs RFEM and RSTAB.

#### 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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