Design moments

The internal forces interpolated from the FE nodes can be found in the design details of the grid point. As the model type 3D was specified in the general data (see Figure 2.1), the moments m_x, m_y, and m_xy, as well as the axial forces n_x, n_y, and n_xy exist in the surface.

The principal internal forces are determined from the RFEM internal forces of the linear analysis. They are determined according to the equations described in chapter 2.3 and chapter 2.4.

For shells, the principal axial forces are shown for both plate sides because they are required for the design as a shell. Unlike the moments, the principal axial forces at the bottom and top surface of the plate are the same.

The design moments are now determined from the principal moments m_I,+z and m_II,+z at the bottom side of the surface. For this purpose, the program first determines the differential angles α_m,+z and β_m,+z between the direction γ_m,+z of the first principal axial force m_I,+z at the surface's bottom side and the two reinforcement directions φ₁ = 0° and φ₂ = 90°.

Now we search for the direction of a moment that stiffens the two-directional reinforcement mesh. As previously shown for walls and plates, only the two angles between the directions of the reinforcement sets qualify as moment directions. The analysis for the surface's bottom side yields these directions for the assumed concrete compression struts:

Only the assumption of the direction γ_m,+z,1 of 85.490° proves to be valid. Since no optimization of this angle is carried out anymore, the final design moments m_end,+z,φ1 and m_end,+z,φ2 are obtained in the direction of both reinforcement sets: