RISAFloor has the ability to model a Semi-Rigid, Rigid or Flexible diaphragm to distribute lateral loads. Click here for more information on the differences between the diaphragm types.
On a beam supported floor, you create a diaphragm edge by clicking this icon: and then choose the Semi-Rigid option. The semi-rigid diaphragm is modeled using plates from the General- Material spreadsheet. The thickness in combination with the material stiffness should be based on the lateral stiffness you expect from your diaphragm.
Existing models can be modified by changing the diaphragm type in the Diaphragms spreadsheet.
In RISA-3D, the diaphragm will provide only “In-Plane” stiffness. In other words, stiffness in the direction of the lateral loads not stiffness for gravity loading. The Semi-Rigid diaphragm will be automatically submeshed in RISA-3D. After a solution is present, you can view the submesh for reference (Model Display Options- Diaphragms tab).