Can I connect a rib member with two surfaces that have different thicknesses? And where can I check the cross-section properties of this composite cross-section? In RFEM, I can only see the eccentric rectangular cross-section and its cross-section properties.

Answer

You can connect a rib member to a line on two surfaces with different thicknesses.

To determine the stiffness or internal forces, the eccentricity of the rectangular cross-section is determined by using the mean value of both connected surfaces in RFEM.

Figure 01 - RFEM Model of Rib with Different Plate Thicknesses

For design in RF‑CONCRETE Members, the add-on module determines a special cross-section, which is displayed in Window "1.4 Ribs" of the add-on module.

Figure 02 - Window "1.4 Ribs" in RF-CONCRETE Members

By clicking the "i" button (see Figure 02), it is possible to open an info dialog box for the generated rib cross-section, where you can see all cross-section properties applied for the design in the add-on module, such as the position of the shear center and center of gravity, and so on.

Figure 03 - Cross-Section Properties of Rib Cross-Section in RF-CONCRETE Members

If adjusting the "effective width" in Window "1.4 Ribs" (for example, to 0.50 m), this has an impact on the cross-section applied in RF‑CONCRETE Members and the cross-section properties of it.

Figure 04 - Modified Cross-Section Properties of Rib Cross-Section

However, this does not affect the stiffness or the determination of internal forces in the 3D model in RFEM.

Keywords

Rib Cross-section property Center of gravity Shear center Plate width

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RFEM Main Program
RFEM 5.xx

Main Program

Structural engineering software for finite element analysis (FEA) of planar and spatial structural systems consisting of plates, walls, shells, members (beams), solids and contact elements

Price of First License
3,540.00 USD
RFEM Concrete Structures
RF-CONCRETE 5.xx

Add-on Module

Design of reinforced concrete members and surfaces (plates, walls, planar structures, shells)

Price of First License
810.00 USD