To define nodes that make up a floor diaphragm, use the following procedure.

1. (Optional) Select a set of nodes which will be used to define the diaphragm.
2. Select the Specifications page in the Analytical Modeling page control bar. The Specifications - Whole Structure dialog opens.
3. On the Specifications - Whole Structure dialog, click Node. The Node Specification dialog opens.
4. Select the Floor Diaphragm tab.
5. Specify the floor level of the diaphragm by either:

   selecting Height and then typing the height of the floor (Y coordinate value)

   or

   selecting YRange and then typing the Minimum and Maximum values of the diaphragm (Y coordinates)

6. (Optional) Select the Define Floor Range option to specify a boundary in the XZ plane of the diaphragm to define its edges:

   select the Select Nodes option to either assign the diaphragm to the current node selection or to assign it later

   or

   select the Floor Range option to type maximum and minimum values in the global X and Z directions to bound the diaphragm

   Nodes lying outside of this selection or range will not be considered to be part of the diaphragm even if they are at the diaphragm height.
7. (Optional) You can specify a control node to use as the center of gravity by selecting the Select Control Node option and then selecting the node number to use as the center of gravity. Otherwise, the program will calculate the center of gravity location for the diaphragm and add an analytical node at this location.
   Tip: To report calculated CGs, add the Cg (Center of Gravity) option in the Post-Analysis Print Commands.
8. Either:

   To…	Do the following…
   add the specification to the model and assign to the diaphragm to the current nodes	click Assign.
   add the specification to the model for later assignment or to use all nodes at the specified Height	click Add.

   The dialog closes.