CSI Software uses cubic interpolation to calculate displacements along frame objects shown on the "Diagrams for Frame Objects" Form that is accessible by right-clicking on a member after the analysis has been run. The coefficients of each cubic function are obtained from the translations and rotations given at the joints on either end of a frame object.
Handling of moving load cases
No displacements are shown on this form for moving load cases, because their results are multi-valued with minimum and maximum value for each displacement. In order to obtain displacements for moving load cases, the user should auto mesh the frame member (via "Assign > Frame > Automatic Frame Mesh") and then view the deformed shape in the main program window (right-clicking on joints when the deformed shape is displayed will show displacements for a particular joint) or in the output database tables for joint displacements.