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• ### Why is there a fully plastic section modulus Zfull and a maximum plastic section modulus Zmax displayed for some cross-sections?

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The fully plastic section modulus Zfull is related to the full-plastic bending moment Mpl,full. For Mpl,full, there is only one internal force available in the respective direction. It is not possible to increase this internal force, even if the cross-section is not perfectly plastic.

On the other hand, the maximum plastic bending moment Mpl,max related to the maximum plastic section modulus Zmax refers to the perfectly plastic state of the cross-section. In this case, the interaction of the internal forces in the y- and z-direction is possible.

• ### Why is there a fully plastic section modulus Zfull and a maximum plastic section modulus Zmax displayed for some cross-sections?

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The fully plastic section modulus Zfull is related to the full-plastic bending moment Mpl,full. For Mpl,full, there is only one internal force available in the respective direction. It is not possible to increase this internal force, even if the cross-section is not perfectly plastic.

On the other hand, the maximum plastic bending moment Mpl,max related to the maximum plastic section modulus Zmax refers to the perfectly plastic state of the cross-section. In this case, the interaction of the internal forces in the y- and z-direction is possible.

• ### I perform a stability analysis of a beam for lateral-torsional buckling. Why is the modified reduction factor χLT,mod used in the design according to DIN EN 1993‑1‑1, 6.3.3 Method 2? Is it possible to deactivate this?

According to DIN EN 1993‑1‑1, 6.3.2.3 (2), the reduction factor χLT can be modified by the f factor for χLT,mod. You can activate or deactivate this option under National Annex Settings.

• ### How is the plastic torsion determined in the plastic hinge definition?

The plastic rotation is determined automatically for each hinge, based on the previously determined cross-section and the member length. For this, the following formula is used:

$\varphi_{y,pl}=\frac{W_{y,pl}\cdot f_y\cdot l_b}{6\cdot E\cdot I_y}$

• ### For the design of a set of members in STEEL EC3, I cannot define effective lengths. Am I doing something wrong?

In addition to the stability analysis in Sections 6.3.1 to Section 6.3.3 of EN 1993‑1‑1 (Equivalent Member Method), RF‑/STEEL EC3 also provides the General Method according to Section 6.3.4 of EN 1993‑1‑1.

This can be extended with the following options:
~ The European lateral-torsional buckling curve, which is regulated in the German National Annex to EN 1993, for example.
~ Extension of biaxial bending according to the dissertation by Dr. Naumes.
~ The interpolation between lateral buckling and lateral-torsional buckling.

When designing sets of members according to the General Method, a window is available in the Window "1.7 Nodal Supports - Sets of Members" where the nodal supports are displayed graphically on the set of members. In this way, the General Method represents a useful supplement to the other design methods, which has proven itself, particularly when designing tapers. It is not necessary to enter effective lengths in this method.

In the "Details" of the add-on module, you can select the method to be used for sets of members in the "Stability" tab (see Figure 01).

The equivalent member method may only be used for straight sets of members with a uniform cross-section (that is, not for tapered joints). For members with a variable cross-section, use the preset General Method.
• ### How can I model and design general bolted connections with the surface and solid elements in RFEM?

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In RFEM, you can model and design connections with the individual dimensions. The video on the left shows an example of modeling and calculation of a rigid bolted connection by using member and surface elements as well as contact solids.

Furthermore, you can define bolt prestressing forces and perform plastic design (RF‑MAT NL add-on module required), for example.

• ### Can RF-STEEL AISC optimize cross-sections for Serviceabillity?

The RF-STEEL AISC module does not optimize cross-sections for the Serviceability Limit State design. Optimization is only calculated for the Ultimate Limit State design.

Users must manually adjust the cross-section in RFEM or within the add-on module and can export the cross-section back into RFEM. In either scenario, the model must be rerun in order to calculate the correct internal forces with adjusted member size.
• ### When creating a material, there are no nonlinear material models available for surfaces or solids. Why?

The nonlinear material models are only available in the 3D environment. Please make sure that the model type is set to "3D" (see Figure 02).
• ### How does the calculation of the moments of inertia differ when the cross-section consists of several unconnected or connected partial cross-sections?

If the cross-section consists of several unconnected partial sections, the sum of the moments of inertia is calculated without the parallel axis theorem components. The cross-section shown in Figure 01 consists of two angle sections that are not connected to each other.

The individual angle sections have the following moments of inertia:

Iy,1,2 = 180.39 cm4 (referred to the centroidal axes y, z)

Iz,1,2 = 65.05 cm4 (referred to the centroidal axes y, z)

The moments of inertia of the entire cross-section result in:

Iy,1+2 = 2 ⋅ Iy,1,2 = 2 ⋅ 180.39 = 360.78 cm4 (referred to the centroidal axes y, z)

Iz,1+2 = 2 ⋅ Iz,1,2 = 2 ⋅ 65.05 = 130.11 cm4 (referred to the centroidal axes y, z)

If the cross-section consists of several connected partial sections, the sum of the moments of inertia is calculated with the parallel axis theorem components. The cross-section shown in Figure 02 consists of two connected angle sections.

The individual angle sections have the following cross-section properties:

A1,2 = 16.25 cm²

yS,0,1,2 = ±2.30 cm (referred to the zero point)

zS,0,1,2 = 3.07 cm (referred to the zero point)

Iy,1,2 = 180.39 cm4 (referred to the centroid axes y, z)

Iz,1,2 = 65.05 cm4 (referred to the centroid axes y, z)

The cross-section properties of the entire cross-section result in:

yS,0,1+2 = 0.00 cm (referred to the zero point)

zS,0,1+2 = 3.07 cm (referred to the zero point)

Iy,1+2 = 2 ⋅ Iy,1,2 + 2 ⋅ A1,2 ⋅ (zS,0,1,2 - zS,0,1+2

Iy,1+2 = 2 ⋅ 180.39 + 2 ⋅ 16.25 ⋅ (3.07 - 3.07)² = 360.78 cm4 (referred to the centroidal axes y, z)

Iz,1+2 = 2 ⋅ Iz,1,2 + 2 ⋅ A1,2 ⋅ (yS,0,1,2 - yS,0,1+2

Iz,1+2 = 2 ⋅ 65.05 + 2 ⋅ 16.25 ⋅ (2.30 - 0.00)² = 301.46 cm4 (referred to the centroidal axes y, z)

• ### I would like to use the CRANEWAY add-on module to design a suspension crane. Where are the design points 0, 1, and 2 for the stress analysis on the bottom flange and for the fatigue design?

The design points in CRANEWAY have been adopted in compliance with the standard. In this case, the stresses are calculated for the following locations:

• Design Point 0

A periphery of the flange at the web edge or at the fillet start

• Design Point 1

A flange at load application point (this can be checked as wheel spacing in Window 1.4)

• Design Point 2

The flange edge
These points are not displayed in the resulting cross-section graphic in the CRANEWAY program. However, there is always a stress point at the design points 0 and 2 for which the result values can be directly displayed.

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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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