The minimum size column and drilled shaft for grade separation structures is 36 in. diameter unless a larger size is noted elsewhere. Column and drilled shaft sizes smaller than 36-in. diameter are permissible for widenings and only to match existing columns.

Analysis and design is not required for round columns supporting multi-column bents when the following conditions are met:

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.

If these conditions are not met, column design and analysis, including second order effects and stiffness reduction from cracked concrete, is required.

For columns subjected to bending under unfactored dead load, satisfy the minimum reinforcement requirements of Article 5.6.7, using half the exposure factor consistent with the site and other bridge elements.

Evaluate concrete tensile stress at Service I and Service IV for prestressed elements.

Where lap splices are not possible see Chapter 5 - Other Designs, Section 6 – Non-Contact Lap Splices for reinforcing splice requirements.

When the design choice is to redirect the collision load, follow the requirements given in Chapter 2 - Limit States and Loads. When the design choice is to provide structural resistance, design for the 600 kip equivalent static load as described in Chapter 2 - Limit States and Loads, Section 2 - Loads.

Design the column to withstand the collision force in shear and flexure. Consider the transfer of this force to the other elements such as bent caps, footings, piles, or drilled shafts. Design all the structural elements for collision forces. Consider the soil response when determining the boundary conditions (i.e. depth to fixity). Neglect the collision load when determining the lateral and bearing pressures for foundation design.

Use of a vehicular deflection wall between the columns is permitted if necessary. Design vehicular deflection wall assembly (columns plus wall) for the 600-kip equivalent static load as described in Chapter 2 - Limit States and Loads, Section 2 - Loads.

No further analysis is required for columns with a gross cross-sectional area no less than 40 sq. ft., a minimum thickness of 5 ft. and column transverse reinforcement is composed of at least No. 4 ties at 12 in. maximum spacing or a No. 4 spiral at 9 in. maximum pitch.