If the Semi-Rigid Diaphragm option is selected, slabs are modeled with shells that take in-plane and out-of-plane deformations into account.
Semi-Rigid Diaphragm: Slab stiffness; It is an analytical model that represents situations where the system stiffness is close to or equal to. The stiffness calculation is calculated depending on the slab thickness, dimensions and material parameters. The semi-rigid diaphragm acceptance is the one that reflects the most realistic behavior of the slab behavior in the structure analysis model.
Location of Semi-Rigid Command
By activating the Semi-Rigid option under the Analysis Model heading in the Analysis and Design menu in the Ribbon Menu, you can solve the slabs with the assumption of a semi-rigid diaphragm.