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• ### How is the buckling load determined in RSBUCK if the most unfavorable value is transferred from RSTAB in the case of a non-constant axial force distribution?

Basically, the buckling load is determined as follows when activating the option to transfer the most unfavorable value of the axial force for a non-constant distribution:

Critical Load Factor * most unfavorable value of the axial force = buckling load

However, the most unfavorable value refers to the member part, not to the entire member. The value of the most unfavorable axial force of the entire member is only assumed as the most unfavorable value if "1" is selected for "Internal member division for", see Figure 1.

Otherwise, the mean value is first determined internally from the most unfavorable values of the respective member divisions. The following diagram shows the most unfavorable value for two member parts from the normal force distribution in the following figure:

(60 kN + 30 kN)/2 = 45 kN

Thus, the following buckling load results for the first buckling mode in this example:

2.429 * 45 kN = 109,3 kN

• ### How does RF-STABILITY or RSBUCK determine the buckling load?According to the manual calculation, the respective buckling loads should be about 10% higher.

It is very likely that the partial safety factor γM for the reduction of the modulus of elasticity is activated in RFEM, but is not considered in the manual calculation.

γM can be viewed and, if necessary, adjusted within the "Edit Material" dialog box, see Figure 1.

Furthermore, in the RF-STABILITY or RSBUCK add-on module, the option "Activate stiffness changes of RFEM" must be considered in the general data, see Figure 2.

With an effective length of 35.405 m, an area moment of inertia of 8356 cm 4 , a modulus of elasticity of 21000 kN/cm² and a partial safety factor of 1.1 as a divisor, the following buckling load results according to the following formula:

• ### How can I design dowel-laminated timber (DLT) or nail-laminated timber (NLT) in RFEM?

Both DLT and NLT are considered to behave more like single-axis beam elements stressed primarily in bending. Although realistically there is a small amount of stiffness perpendicular to the span direction, this is neglected in beam design. This is in contrast to cross-laminated timber (CLT) which includes two-way stiffness in both the directions parallel and perpendicular to the span direction. Therefore, RF-LAMINATE is not the suitable add-on module to NLT or DLT design but rather used for CLT design.

The best approach in RFEM is to model a standard stiffness surface with modified orthotropic elastic 2D material properties. For the material model details, the modulus of elasticity in the local y-axis direction (Ey) should be set to a very small number (i.e. 0.001). The shear modulus in the local yz-plane (Gyz) should also be set to this small value. This will replicate little to no stiffness in the direction perpendicular to the DLT or NLT span direction.

The surface can then be applied in the RFEM model for the full analysis. Note, design is not possible for these elements directly in RFEM. Internal forces, stresses, deflections, etc. from the RFEM analysis can be exported to alternative programs (i.e. Excel) for further design according to the various standards.

• ### How is the support spring calculated for a wall?

The support spring is determined from the modulus of elasticity (E), the cross-sectional area of the wall (A) and the height of the wall (H) as follows:

Since the display of the spring for the linear meter is displayed, the unit kN/m² results, see Figure.

• ### How to model a cable net structure in using the RF-FORM-FINDING add-on module?

Because a net requires multiple cable segments to be modeled in a grid-type pattern, the cables are not one continuous member. This is not ideal for the RF-FORM-FINDING module as the cable prestress properties such as sag, target length, or force are best applied to a single cable segment. The program cannot easily apply these settings to a cable that is broken down into multiple segments along its length.

The best option to model the net in RFEM is to instead use a surface element. The material and stiffness properties of the surface are the equivalent properties to that of the net provided by the manufacturer. RF-FORM-FINDING can then be applied to the surface element such as a prestress force or stress.

• ### I have version 5.24 and the calculation takes me longer than in previous versions for the same model. What is the reason for this?

New

004847

In version 5.23, the possibility of calculating the maximum deformation has been added, which finds the largest total deformation (in the case of nonlinear material also plastic deformation) for members, for surfaces and for solids. The calculation of the maximum deformation value is switched on by default. If you disable this option, the calculation should speed up.
• ### Is it possible to renumber cross-sections and materials in RFEM and RSTAB?

New

004845

Cross-sections and materials cannot be renumbered directly in RFEM or RSTAB.

In this case, it is necessary to carry out a small workaround. The following example shows the renumbering of cross-sections by means of Excel tables:

1. First, the selected areas "Cross-Sections" and "Members" are exported as an Excel table. Since members are linked to a cross-section, they must also be changed.
2. In Excel, the cross-sections are renumbered correctly.
3. These must also be correctly assigned to the members. The filter option can help you here.
4. After editing, both tables must be imported back into RFEM or RSTAB.

• ### What should be considered when using a failure of columns under tension in the RF‑/DYNAM Pro - Equivalent Loads add-on module?

In order to consider the failure of certain members when using RF‑/DYNAM Pro - Equivalent Loads, proceed as follows:

1) Deactivating the corresponding members for the eigenvalue determination within the corresponding load case, see Image 01 (add-on module, tab Natural Vibration Cases, Calculation Parameters) and Image 02 (main program, Calculation Parameters, Deactivate and select).

2) Determining dynamic load cases from RF‑/DYNAM Pro by using the calculation, then deactivating the corresponding member in the main program within the global calculation parameters of the dynamic load cases, see Image 03.

• ### I get the error message "Entry in the 'Beam spacing' box is not within the allowable range." What can I do?

You have probably defined a shear panel and a rotational restraint for your design case in the RF‑/STEEL EC3 add-on module, but have not yet defined all specifications for the rotational restraint.

In Window 1.13, scroll down under Settings. For the rotational restraint, the "spacing of beams" is still defined as s = 0 m. Adjust the value accordingly.

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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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