Each column in the substructure is modeled as series of straight and vertical space-frame elements with 6 DOFs per node. The same criteria are used for cross sections in the column as in the superstructure. A second bending moment of inertia is required because of the use of a space-frame element.

Columns within piers are fixed at their tops. The connection between the tops of columns for both integral and drop-cap piers is infinitely stiff; in other words, the cap is not modeled and each column will displace vertically the same amount in the absence of torsion in the superstructure. Each column may have different flexible lengths and each column can have its own material properties as defined in the Concrete Material dialog box.

The analysis model generated for integral piers places the tops of columns (and, hence, the location of any force release between the superstructure and the pier) at a distance Y-bottom from the superstructure, where Y-bottom equals the distance from the center of gravity of the superstructure cross section to the extreme bottom fiber. The lateral location of the columns is such that the pier connection to the superstructure is at midpoint of the two exterior columns.

The analysis model generated for drop-cap piers places the tops of columns at a distance (Y-bottom + Soffit-to-Bearing + Bearing-to-Cap + Cap Height) from the superstructure. Any specified force release is applied at a distance (Y-bottom + Soffit-to-Bearing) from the superstructure. You can specify the dimension parameters for a drop-cap pier as zero (0) if you do not want to include the distances in analysis model. However, there is no program option to ignore using the Y-bottom.