#### Further Information

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• ### Is it also possible to check the punching shear on vertical walls?

Yes, it is possible to also perform punching shear designs for vertical walls.

Please note, however, that this feature was not available in the first versions of RF‑PUNCH Pro. For this, you will need RFEM 5.08 or later.

• ### Does RWIND Simulation apply a boundary layer model?

In RWIND Simulation, each model surface in the wind flow is treated as a "smooth" wall. This definition results in a boundary layer in the areas around the flow close to the walls, which has an influence on the velocity profile perpendicular to the wall depending on the air viscosity. This boundary layer is created in RWIND Simulation according to the so-called "wall law." This law describes the velocity profile perpendicular to the wall and can be represented by the dimensionless variables u+ and y+.

Dimensionless variable u+:
$\mathrm u^+=\frac{\mathrm U}{{\mathrm u}_{\mathrm\tau}}$
where
U is the velocity on the wall,
uτ is the frictional velocity.

Dimensionless variable y+:
$\mathrm y^+=\frac{{\mathrm u}_{\mathrm\tau}\cdot\mathrm y}{\mathrm\nu}$
where
y is the wall distance,
uτ is the frictional velocity,
ν is the kinematic viscosity of the air.

Using the friction velocity uτ:
${\mathrm u}_{\mathrm\tau}=\sqrt{\frac{{\mathrm\tau}_{\mathrm w}}{\mathrm\rho}}$
where
τw is the shear stress,
ρ is the air density.

By describing the boundary layer model in the viscous partial layer directly next to the wall
$\mathrm u^+=\mathrm y^+$

and in the subsequent logarithmic layer
$\mathrm u^+=\frac1{\mathrm\kappa}\cdot\ln\;\mathrm y^++\mathrm C$

you obtain the following velocity distribution,

where
κ is the Kármán constant (κ = 0.41 for the simulation of a smooth wall),
C is the constant (C = 5 for the simulation of a smooth wall).

To ensure that the solution process is relatively fast and robust, the program specifies the corresponding boundary layer model directly in the first cell next to the model surface. The remaining part of the boundary layer results from the solution of the globally applied Navier-Stokes equations.

• ### Why is an opening not taken into account when determining the punching load due to shear forces in the critical perimeter?

When determining the punching load from shear forces in the critical perimeter, a continuous perimeter is applied.

If an intermittent perimeter was to be used when determining the punching load, the load component (along the intermittent length) might not be considered. This would be the case, for example, if you have only defined the opening in RF‑PUNCH Pro, but not in the RFEM model. In the RFEM model, the shear force would be generated by using the continuous cross-section. If the component were neglected, there would be too small punching load determined.

Therefore, the intermittent control perimeter is always applied in RF‑PUNCH Pro when determining the punching load from the shear forces within the critical perimeter.

During the design (on the resistance side), the opening is considered again and the perimeter section is reduced accordingly.

• ### In the RF‑/STEEL add-on module, I am trying to design a cross-section created in SHAPE‑MASSIVE. However, the cross-section is classified as invalid. What is the reason?

In this case, take a look at the stress points in the cross-section details. If they are not accessible (grayed out), no stress points have been defined in SHAPE‑MASSIVE and the design is not possible. In SHAPE‑MASSIVE, it is necessary to activate the "Stresses by Stress Points" option in General Data. After recalculating and saving, the cross-section can be designed in the RF‑/STEEL add‑on module.
• ### I would like to perform punching shear design on a column with downstand beams as a wall corner or wall end. However, the module applies an internal column. Is it possible to adjust it?

RF-PUNCH Pro tries to automatically detect the correct geometry of the node of punching shear from the model input and to specify it correctly.

Depending on the entered data, it may be necessary to adjust the preset geometry. For example, because a column is recognized on a wall corner instead of punching shear design. You can change this in Window 1.5, so that the correct punching geometry can be selected, if necessary.

• ### Is there an easy way to create a spatial structure from a 2D model, whereby the nodes in columns and lines will be extruded into walls?

For lines, this option is already available directly in the shortcut menu. For extruding nodes into members and lines in surfaces, there is the corresponding option in the detailed settings of Copy/Rotate/Mirror. As soon as at least one copy is generated, the new elements will also be created.
In case this feature is not wanted anymore, it should be deactivated in the detailed settings again.
• ### When modeling a building, there is a location where I have a wall on a ceiling that is not supported underneath. What are the modeling options for this?

If the load-bearing capacity of the wall surface is neglected and only applied to the ceiling as a load by using a line load, it would result in very large deformations.
If the nonlinear property of the masonry is not considered, it would result in very small deformations.
In principle, there are three options available in RFEM.
• Line release: Vertical compression forces are only transferred. In this case, the nonlinear property is only applied for the force transmission directly to the connection line of both surfaces.
• Nonlinear material "Isotropic Masonry": In this case, the tension stresses in the x- and y-direction (that is, vertical and horizontal) are reduced iteratively to the specified limit values by reducing the stiffness. Using this model, it is possible to represent the behavior of a masonry wall that is closest to reality, because the tension stresses are reduced in the direction of the mortar joints. This requires the RF‑MAT‑NL add-on module.
• Nonlinear surface stiffness type "Membrane without tension": In this case, the tension stresses in the principal stress direction are reduced iteratively by reducing the stiffness.
• ### How can I perform a stability analysis or walls in RF‑CONCRETE Surfaces?

Currently, there is no option to perform a stability analysis in the RF‑CONCRETE Surfaces add-on module. However, you can use a result beam to perform a simplified design by means of the nominal curvature method in RF‑CONCRETE Columns.
• ### I get an error message saying that the support of type Wall cannot be defined on a rotated line. How can I fix the problem?

The reason for this message (Figure 01) could be a rotated line imported from CAD, for example. Once you set all rotations of the lines to 0° (Figure 02), the message should no longer appear.
• ### I would like to use a cross-section that is not included in the cross-section library of RFEM and RSTAB. Is it possible to get the cross-section?

By using the add-on modules SHAPE‑THIN (thin-walled cross-sections) and SHAPE‑MASSIVE (thick-walled cross-sections), it is possible to model almost any cross-section by entering them graphically, in tables, or by importing a DXF file.

For SHAPE‑THIN and SHAPE‑MASSIVE, there are the connection possibilities to RFEM and RSTAB. Thus, the cross-sections can be transferred to RFEM and RSTAB, calculated, and designed in the add-on modules.

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If not, contact us via our free e-mail, chat, or forum support, or send us your question via the online form.

#### 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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