Use the Edit menu > Add/Edit Tendons > Add Tendons to Beams command to add a tendon to selected beam objects.
Select the beams (not columns or braces) where a tendon is to be added, and use the Edit menu > Add/Edit Tendons > Add Tendons to Beams command to immediately add a tendon to the selected beam objects. The program adds a single tendon that follows the plan centroid of the selected beams. A reverse parabola is used for the vertical profile over the beam depth.
Also see