#### Further Information

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• ### 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).
• ### Why can I specify a "creep-producing permanent load" in RF‑CONCRETE Columns and not in RF‑CONCRETE Members?

The RF‑CONCRETE Columns add-on module allows you to define a "creep-producing permanent load." You can find the corresponding tab in Window "1.1 General Data."

The reason for the entry is that RF‑CONCRETE Columns can apply this "creep-producing permanent load" for the automatic determination of the effective creep ratio according to EN 1992‑1‑1, 5.8.4.

In contrast, there is no explicit input option for this creep-producing permanent load in RF‑CONCRETE Members. In RF‑CONCRETE Members, the stability analysis of reinforced concrete columns by means of nonlinear design does not automatically reduce the effective creep ratio. You can find the background to the effective creep ratio applied in RF‑CONCRETE Members in Chapter 2.4.6 of the RF-CONCRETE Members manual.

The same applies to the CONCRETE Columns or CONCRETE add-on modules for RSTAB.

• ### 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 do I get the message 28) in RF‑CONCRETE Members, saying that I have to make a "calculation without second order effect" with the internal forces according to the gemetrically linear analysis?

RF-CONCRETE Columns determines the equivalent moment M0e from the moment M02 at the column head and M01 at the column base according to EN 1992‑1‑1, 5.8.8.2 (2), and performs the design according to the model column method with this equivalent moment M0e.

Now, it may happen, for example, that a computationally larger required reinforcement area would result from the cross-section design with the moment M01 at the column head.

To ensure this, message 28) is displayed, according to which the user should perform a standard design with the internal forces according to the linear static analysis. To do this, simply open the RF‑CONCRETE Members add-on module and perform pure design of the internal forces according to the linear static analysis for the member designed in RF‑CONCRETE Columns.

• ### How can I quickly model a chimney with reinforcement rings and stiffeners?

In RFEM, the easiest way is to use the "Plane Surfaces" → "Annulus" feature. This allows you to model the reinforcement rings very quickly and easily. Then you can extrude the inner line into a surface, the chimney is already generated. Now, the existing annular surface is copied upwards and the corresponding stiffeners are modeled. You can use the "Rotate" command to distribute the stiffeners over the chimney perimeter.

• ### Is it possible in RFEM and RSTAB to completely define a member by entering the data in tables?

Yes, it is possible.

You can enter all the data necessary for:
• Nodes
• Lines
• Materials
• Cross-Sections
• Supports
All of them can be entered in the tables provided for this purpose.

If the cross-section description from the Dlubal cross-section library is known, this can also be entered directly in Column A in Table 1.13. Otherwise, you can use the cell to open the cross-section library.

This is also possible in RSTAB. Here, it is not required to enter the line. This is only necessary in RFEM.
• ### What is the difference between the materials Isotropic Plastic 1D and Isotropic Nonlinear Elastic 1D?

The difference between both material models is as follows:

In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state after the load relief.

In the case of the Isotropic Plastic 1D material model, the plastic deformation is considered.

For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible in both models to define the distribution after the last step.

The Isotropic Nonlinear Elastic 1D material model allows for the anti-symmetric input of the stress-strain diagram (different for the positive and negative zone), whereas the isotropic Plastic 1D model only allows for symmetric input.

• ### I recently purchased RSTAB with the CONCRETE add-on module. Can I use it to perform the stability analysis of reinforced concrete columns?

Yes, you can, because the nonlinear reinforced concrete design is also included in the CONCRETE add-on module for RSTAB 8. Thus, you can activate "Nonlinear calculation" in the "Ultimate Limit State" tab.

In the detail settings for the nonlinear calculation, you can select "General design method for members in axial compression acc. to second order theory."

In this case, it is important to define the imperfections in RSTAB and apply load combinations (CO) according to the second-order analysis, no result combinations (RC), for the design!

###### Note to RFEM 5:

In RFEM 5, the same procedure is possible in RF‑CONCRETE Members. However, RFEM requires the RF‑CONCRETE NL add-on module for the nonlinear reinforced concrete design.

• ### Is it possible to enter a curtailed reinforcement in RF‑CONCRETE Columns?

No, it is not possible.

A member or a set of members is designed by the model column method as a "structural component."
It means that the longitudinal reinforcement is constant over the entire length of the structural component.

The design is carried out by means of the governing internal forces at the governing location of the structural component (a member or a set of members).

The stability analysis involving a curtailed reinforcement over the column can be performed by using the nonlinear analysis of compression elements in RF‑CONCRETE Members (RFEM) or CONCRETE (RSTAB).

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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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