Project Overview
This two-lane, three-span bridge features a 240 ft (74 m) center span, the longest simple-span precast concrete, post-tensioned, spliced-girder bridge in the United States. The main span is anchored by a pair of 120-ft-long (37 m) adjacent box-beam spans.
The center span comprises five modified New England Bulb Tee (NEBT) girder lines, each consisting of three segments of 64 ft, 108 ft, and 64 ft (20 m, 33 m, and 20 m). This final configuration evolved during the permitting process after state environmental regulators prohibited a permanent pier in Otter Creek. A design-build delivery system, the first to be used on a major transportation project in Vermont, greatly accelerated completion.
Precast Solution
The precaster used 10,000 psi (69 MPa) self-consolidating concrete to meet the design demands on the large girders. The approach spans each feature 10 adjacent box beams cast using 8000 psi (55 MPa) self-consolidating concrete. Coordination with the precaster throughout the design of the girders and development tof the fabrication drawings allowed timely modifications to existing precast concrete forms and helped expedite fabrication.
With girders standing nearly 10 ft (3 m) tall, the ceiling heights of the precasting plant were just high enough to lift the beams onto the transport trailers. Girder segments were erected using a single Manitowoc crane with a 160-ft (49-m) boom capable of hoisting the 93-ton (84-tonne) segments into place. Once erected, the girder segments had closure pours filled with cast-in-place concrete, and the cast-in-place diaphragms between girder lines were constructed.
Designed to be low maintenance, the bridge features an 8 in. (200 mm), cast-in-place concrete deck with 3 in. (75 mm) of pavement and 6-ft-wide (2 m) sidewalks with precast concrete architectural features and lighting. A pedestrian overlook was created on each of the four piers along the creek channel. The use of precast concrete superstructure materials saved design and construction time and brought another level of efficiency to the project. |