Bridge Description

60-day construction of new prestressed concrete deck bulb T girder bridge for extension of a bypass route

on O’Malley Road Eastbound over C Street in the Municipality of Anchorage in southern Alaska

Tier 5 (within 3 months)

ABC: 60-day construction

Conventional: ABC is conventional construction in Alaska

improved site constructability; reduced onsite construction time; improved work-zone safety; improved material quality and product durability; reduced life-cycle cost

223-ft long and 39-ft wide two-span prestressed deck bulb T girder bridge (110 ft – 110 ft)

30000

ABC is conventional construction in Alaska due to climate and terrain

The bridge has two 11.8-ft-wide traffic lanes (one lane in each direction), an 8.2-ft-wide shoulder, and a 4.3-ft-wide shoulder. The cross-section consists of six adjacent pretensioned decked double-tee girders with 6.5-ft-wide top flange and 4.5 ft depth. The interior pier consists of a cast-in-place concrete pile cap on steel pipe pile extensions. The cast-in-place abutment is founded on steel H-piles.

The girders were fabricated at a precast plant and trucked to the site. The contractor drove the steel H-piles and constructed the cast-in-place abutments, and drove the steel pipe piles and constructed the cast-in-place pile cap. The girders were erected with a truck crane onto elastomeric bearing pads. They were welded to each other at embedded shear connectors spaced at 4 ft along flange edges. Grout was placed in the longitudinal shear keys and the shear connector blockouts between girders. Closure joints at the ends of the girders were cast. Curbs were cast, and metal railing was installed. A waterproof membrane was placed on the deck, followed by an asphalt overlay.

This bridge is one of a pair of bridges constructed at this site. These bridges were part of a large roadway project. These bridges were built in about 60 days. They would likely have been opened to traffic sooner, but the bridge subcontractor had to wait for the earthwork to catch up.

This type of bridge is quite common in Alaska. Most are built in one summer construction season – about 5 months maximum. The time is not determined so much for traffic and user impacts but rather for weather and climate limitations. That is, this bridge is not unique in the rate at which they were built — it’s just the way that this style of bridge is built.

Precast concrete girders and deck f’c > 7,500 psi