Column spacing does not exceed 18 ft.

Column height, measured from bottom of the cap to top of drilled shaft or footing, does not exceed 12 times the column diameter (measured in feet). Example: 36 ft. height limit for a 3-ft. diameter column. For drilled shaft foundations in stream crossings, the bottom of the column is to be taken at the bottom of the scour envelope.

Columns are reinforced with the minimum amount of reinforcement, both longitudinally and laterally, as prescribed in AASHTO.

Columns meet these size requirements based on superstructure type:

Slab spans: 24 in. for stream crossings, 36 in. for grade crossings
Pan form spans: 24 in. for stream crossings, 36 in. for grade crossings
Slab beam and spread slab beam spans: 24 in. for stream crossings, 36 in. for grade crossings
Box beam and spread box beam spans: 36 in.
Types Tx28 through Tx54 girder spans: 36 in.
Types Tx62 and Tx70 girder spans: 42 in.
U40 and U54 beam spans: 36 in.
For other beam types, compare drilled shaft load to what would be expected using one of the preceding superstructures, and use a column diameter as appropriate.