Diaphragm section forces at a user-defined cross-section location are calculated by the program. This feature is similar to the section cut feature for shear walls. Calculated forces are equilibrium-based force/moment resultants. Note that this feature is available only for meshed diaphragms (i.e., for semirigid diaphragm or for diaphragm with two-way decks).

The engineer should ensure that the Store diaphragm forces option is checked in the General Criteria dialog before analysis is conducted. Otherwise, no section forces are calculated. In addition, Calculated diaphragm forces at user-defined locations are displayed in Diaphragm Section Forces report.

In order to view diaphragm cross-section forces, you must first be in plan view for a diaphragm. Select Reports > Diaphragm Forces. The mouse pointer changes to a "+". Click and two points to draw a vertical, horizontal, or sloped line across a diaphragm. Once a valid cross-section line is drawing, the Diaphragm Section Forces report for that cross-section opens. This report shows the calculated force and moment resultants at mid-length of the line.

The report includes force resultants (axial, major shear, and minor shear) as well as moment resultants (major moment, minor moment, and torsion) reported at mid-length. The reported forces and moments follow the following sign convention:

It is important to note that the program always report the resultants resolved on left side (or above) of cross-section. Several examples are shown in the following figure (i.e., reported values are those on marked left or above side of cross-section line). In addition, local axes of cross-section are set in a way that local axis 1 is always along the line, from left-to-right or from bottom-to-top; local axes 2 is on the plane of the diaphragm following right-hand rule and local axes 3 is perpendicular to axes 1 and 2 (i.e., perpendicular to the plane of the diaphragm).

In addition, results of force/moment values at discrete points along section cut is calculated. Contrary to cross-section resultants, discrete location values show variation of forces and moments along section cut. Note that number of discrete point locations increases when mesh density is increased.