It is the assumed diaphragm to transfer horizontal forces to the structure without slab in-plane deformations.
With Rigid Diaphragm Behavior;
Story masses can be defined at the center of mass of the slab.
Since the number of unknowns is low, rapid analysis is performed.
Beams do not receive axial force.
Preferred building types;
Gapless slab structures without plan irregularities
Structures in which story slabs safely transfer horizontal forces to the carrier system in their own planes.
The slab is considered to be in-plane infinitely rigid and does not change shape.
When we compare the rigid diaphragm and semi-rigid diaphragm models, different displacement values are seen in the middle region of the models.
The maximum displacement in the rigid diaphragm version is 0.035 millimeters.
You can review page 93 of the ideCAD Finite Elements Guide.
Diaphragm Modeling Selection
To model a rigid diaphragm, select the diaphragm modeling method from the Analysis Settings dialog.