One unique feature available in Substructure is Combined Footing Design. This feature allows the ability to design and analyze a footing under multiple columns. It includes three options: Combined Rectangular Footing, Combined Trapezoid Footing, and Strap Footing. Note that strap footing is only available for a footing covered by two columns.

Before you can design a combined footing, you must select more than one column under Columns on the Footing screen. If the combined spread or Combined pile footing is a rectangular or trapezoidal footing, you may specify that directly on the footing screen. However, if the footing is a strap, you must define the footing geometry before any design can take place (using the Libraries | Footing Configuration option).

If you selected more than one column and the spread footing type, the Combined Spread Footing Design screen displays, as shown below.

Begin by inputting the pile/shaft cap configuration information. You can specify the footing size in one of two ways. First option is to select User Input and then specify length (X) and width (Z). Second option is to select the From Library and then choose one of the footings. The Description list (previously defined using the Libraries | Footing Configuration option). If the footing is symmetrically placed (concentric) under the column which is the most common case, select that option. However, if the footing is not symmetrically placed under columns, select placed with respect to first column option. In this case, specify the distance of edge of footing from column centerline.

Spread/Cap Depth is the depth of the footing, in global Y-direction, measured from bottom of footing. Length and width multipliers can be specified only when footing From Library option is selected. These are the factors that will be multiplied to the original footing length and width, defined under the Libraries | Footing Configuration option.

Start by inputting the footing size by selecting the footing from the Description menu (previously-defined under the Libraries | Footing Configuration option) and inputting the values in the text boxes.