RF-CONCRETE Surfaces Version 5

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RF-CONCRETE Surfaces Version 5

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3.3.2 Nonlinear Method

Nonlinear Method

Performing a design according to the Nonlinear method requires a license of the add-on module RF-CONCRETE NL. This method for the serviceability limit state design is described in detail in chapter 2.8.

Figure 3.19 Window 1.3 Surfaces for nonlinear check method, Stress Check tab

The following columns are described in the previous chapter 3.3.1:

  • Material
  • Thickness
  • wk,-z(top) / wk,+z(bottom)
  • σc,max
  • σs,max

For orthotropic surfaces, no serviceability limit state design according to the nonlinear method is possible.

The values in the columns D through J are controlled in the tabs below. The settings specified in them are applied to all surfaces by default. It is also possible to only assign the current settings to specific surfaces: Clear the All check box. Then, enter the numbers of the relevant surfaces or use to select them graphically. With you can assign the current settings to these surfaces.

The assignment is only applicable for the active tab, for example Stress Check.

Creep Coefficient φ

The parameters for creep must be defined in the Creeping tab (see Figure 2.144). Based on these conditions, the program determines the creep coefficient φ. For the effective component thickness h0, the program applies the surface thickness d.

Determining the creep coefficient is described in chapter

Shrinkage εcs

This column shows the shrinkage strain. The relevant parameters are defined in the Shrinkage tab (see Figure 2.147). Based on these conditions, the program determines the shrinkage strain εcs. For the effective component thickness h0, the program applies the surface thickness d.

Determining the shrinkage strain is described in chapter If you do not wish to apply any shrinkage strain to a surface, set a user-defined shrinkage strain of zero in the Shrinkage tab and then assign it to the surface.

For pure plates that are defined as the model type 2D - XY (uZXY), shrinkage cannot be considered: There are only degrees of freedom for bending.


This value represents the maximum allowable deformation that must be observed in the design of the serviceability limit state. The design criteria are defined in the Deformation Analysis tab.

Figure 3.20 Window 1.3 Surfaces, Deformation Analysis tab

The serviceability for "common structures", for example according to EN 1992-1-1, clause 7.4, is ensured if the deflection in the quasi-permanent action combination does not exceed the following limit values.

Table 3.2

Common case:

Structural elements for which excessive deformations can result in subsequent damages:

The Minimum border line, Maximum border line, and User-defined relative options determine, which effective length leff is applied. For the two border line options, the program applies the smallest or largest border line of the respective surface.

Figure 3.21 Maximum and minimum border line for determining uz,max

When you choose the User-defined relative option, you can enter the length directly or select it graphically between any two points in the RFEM model with . In addition, you must define a divisor by which the lengths are divided for all three options.

It is also possible to specify the allowable maximum deformation uz,max as User-defined absolute.

Related to

The deformation design criterion uses the deflection of a surface – the vertical deformation relative to the straight line connecting the points of support. The Deformation Analysis tab (see Figure 3.20) provides three options for calculating the local deformation uz,local applied in the design.

Table 3.2

Undeformed system:

The deformation is related to the initial structure.

Displaced parallel surface:

This option is recommended for an elastic support of the surface. The deformation uz,local is related to a virtual reference surface that is displaced parallel to the undeformed system. The displacement vector of the reference surface is as long as the minimal nodal deformation within the surface.

Figure 3.22 Displaced parallel surface (displacement vector: minimal nodal deformation uz,min)
Table 3.2

Deformed reference plane:

If the support deformations of a surface differ considerably from each other, you can define an inclined reference plane for the deformation uz,local that is to be designed. This plane must be defined by three points of the undeformed system. The program determines the deformation of the three definition points, places the reference plane in these displaced points, and then calculates the local deformation uz,local.

Figure 3.23 Displaced user-defined reference plane