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In RFEM, you can design surfaces and members of reinforced concrete.Members are designed in the addon module RFCONCRETE Members or RFCONCRETE Columns.Surfaces are designed in the RFCONCRETE Surfaces addon module (optionally with RFCONCRETE Deflect or RFCONCRETE NL).Reinforced concrete solids can not be designed in RFEM. There is currently no addon module for the reinforced concrete design of solids.However, you can create solids with the material "Concrete" and select For example, you can determine the stresses within the solid. Optionally, you can insert a result beam into the solid that is used to convert the results of the solid into member internal forces.The result beam can subsequently be designed in RFCONCRETE Members or RFCONCRETE Columns. 
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The concrete tensile strength f _{ct, eff, wk} = f _{ctm} x crack width factor is applied. 
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No, this is unfortunately not possible. 
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In this case, the method of check and the type of the 2D position are important.When using the analytical method (RFCONCRETE Deflect), it is possible to perform a calculation in 2D positions. When using the nonlinear method (RFCONCRETE NL), the calculation for 2D XY (u _{Z} / φ _{X} / φ _{Y} ) is not possible. In the nonlinear calculation, among others Shrinkage is represented internally as an expansion load, which is not possible in this type of 2D position due to the limited degrees of freedom.Convert 2D to 3D PositionIn the general data, it is possible to simply convert a 2D position into a 3D position. For the supports, all degrees of freedom not contained in the 2D position are fixed when converting to a 3D position (see the video). 
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The detailed procedure can be found in the video. It indicates the most important features:

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In SHAPEMASSIVE, the reinforced concrete design has to be activated in the General Data section. As soon as the design is active, it is possible to set the design accordingly in a separate tab (Figure 01).There are three types for the design:StrainStress Distribution (Example 01):It is possible to determine an available design ratio by specifying the internal forcesExisting Safety (Example 02):There is determined a state of fracture (ratio = 100%) and a safety in relation to it.Design (Example 03):By specifying a maximum and minimum diameter or a minimum and a maximum reinforcement, it is possible to increase the reinforcement within the design.Irrespective of which of the three methods is used, it is necessary to specify the position of the reinforcement and an acting internal force (Figure 02). 
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The program COMPOSITEBEAM for the design of composite beams is effected in accordance with ENV 199411: 199210. This standard specifies a composite profile consisting of steel sections and reinforced concrete.The design of composite beams consisting of timber and reinforced concrete is carried out according to EN 199513. In this case, the timedependent load states t=0, t=37 years and t= unlimited have to be analyzed in particular. These states are usually taken into account by means of impressed strains. This is done manually in the RFEM program. For this and many other reasons, it is not possible to design timberconcrete composite beams in the COMPOSITEBEAM program.However, on our homepage you can find a lot of information about the design of timberconcrete composite beams, for example here. 
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Two planar structural components can be defined in the RFLAMINATE addon module via the Hybrid material model (Figure 1).In this case, the automatic input of a crosslaminated timber plate would according to the manufacturer's specifications also be possible (see Figure 2).However, the disadvantage of the input in the RFLAMINATE addon module consists in the requirement for a rigid connection. This is not the case for a timberconcrete composite construction. Thus, the calculation is only an approximation.Another possibility is to couple two surfaces via a surface release or a contact solid. The advantage is that you can define almost any shear transfer this way (Figure 3). In the RFEM model file attached here, this has been defined in the middle second model.The third option would be to define a hybrid member as specified in the third model of the attached file. In this case, however, the biaxial load transfer of the structure will not be considered. However, this method has the advantage of highly automated design. This is also explained in this FAQ . 
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The crack moment of a concrete crosssection is calculated from the mean tensile strength of the concrete and from the ideal section modulus. The crack moment describes the internal force that occurs when the tension stress f_{ctm} is reached in the outermost fiber of the crosssection and crack formation occurs.For uniaxial bending, it is possible to calculate the crack moment analytically. For biaxial bending, the introduction of a weighting factor k is helpful in order to determine from the components M_{cr,y} and M_{cr,z} M_{cr}.
Calculation for the attached example:Bending moment M_{y} = 20 kNmBending moment M_{z} = 20 kNmIdeal section modulus W_{y} = 3081 cm^{3}
Ideal section modulus W_{z} = 3081 cm^{3}^{}Mean tensile strength of concrete f_{ctm} = 0.290 kN/cm^{2}Member 1: Uniaxial bending M_{y}:$\begin{array}{l}M_{cr\;}=f_{ctm}\times W_y\\M_{cr\;}=0,29\;\frac{kN}{cm^2}\times3081\;cm^3\\M_{cr\;}=893\;kNcm\;=\;8,9\;kNm\end{array}$Member 2: Uniaxial bending M_{z}:$\begin{array}{l}M_{cr\;}=f_{ctm}\times W_z\\M_{cr\;}=0,29\;\frac{kN}{cm^2}\times3081\;cm^3\\M_{cr\;}=893\;kNcm\;=\;8,9\;kNm\end{array}$Member 3: Biaxial bending M_{y} and M_{z}:$\begin{array}{l}M_{cr\;}=\sqrt{M_{cr,y}^2+M_{cr,z}^2}\\M_{cr,y\;}=k\times My\\k=\frac{f_{ctm}}{\sigma_M}\\\sigma_M=\frac{M_y}{W_y}+\frac{M_z}{W_z}=\\\end{array}$ 
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Yes, it is because the CONCRETE module of RSTAB 8 also includes the nonlinear reinforced concrete design. Thus, you can activate the 'Nonlinear Analysis (State II)' in the 'Ultimate Limit State' tab.
Figure 01  Dialog Box 'General Data' in CONCRETE
In the detail settings for the nonlinear design, you can select the 'General Design Method for Members in Axial Compression acc. to Second Order Theory'.
It is important that you define the imperfections in RSTAB and apply load curves (CO) according to the secondorder analysis for the design, no result combinations (RC)!
Note on RFEM 5:
In RFEM 5, the same procedure is possible in RFCONCRETE Members. However, the addon module RFCONCRETE NL in RFEM is required for the nonlinear reinforced concrete design.
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