Large Concrete Column - Plastic Hinge?

[justhumm]

I am working on a bridge replacement / rehabilitation. A few of the concrete piers are being replaced in kind. The pier columns are large (14 x 15 ft +/-) and are flared out (not just a vertical section) at the bottom near the pedestal.

I am still waiting for another office to complete a Soil-Structure-Interaction analysis to provide more information about the plastic hinge location, but I started looking at the plastic hinge zone requirements. (AASHTO 6ed, 5.10.11.3, et. al.)

The bridge is in seismic zone 2 and AASHTO specifies to detail it for zone 3 & 4 requirements. This requires confinement tie vertical spacing of about 4 inches and a lot of seismic ties confining the vertical bars in the hinge zone. If it were just a "regular" 3 ft diameter pier column, it would kinda' make sense, but when thinking about the size of the columns, this type of random detailing seems like an excessive amount of reinforcing steel.

Does anyone know of any published studies or documents dealing with large reinforced columns and plastic hinges?...recommended reinforcement details or justification for neglecting the confinement requirements for a plastic hinge?

Thanks for any comments!