Learn how to define supports for the frame structure.
In the Standard toolbar, expand the Layouts drop-down menu and select Supports.
The layout is divided in three parts: View, Supports dialog and Supports table.
Click Fixed from the list in the Supports dialog.
Place the cursor in the Current selection box, and then select the lower column nodes in the drawing area. To easily select all the lower column nodes, click and hold the left mouse button while you draw a rectangle around the nodes 1 and 3.