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I-91 Brattleboro Bridge



PROJECT APPROACH AND INNOVATIONS

The FIGG/PCL Design/Build Team provided creative solutions to the project challenges including the use of balanced cantilever construction, eliminating the need for temporary falsework in the West River. The balanced cantilever method facilitated construction to rise above the site constraints on the ground below, and allowed the long spans to be formed in a self-supported manner during construction. This was an important benefit for the unobstructed use of the West River and West River Trail for recreation. Using self-advancing form work (form travelers), segments of the bridge were cast-in-place 16 feet at a time, alternating from one side of the pier to the other, until each cantilever arm reached 257 feet. When the adjacent pier’s cantilever was complete using the same process, a small closure segment was cast to connect the two cantilever arms and form the span. For the two cantilevers to meet at a precise mid-air target, surveying and geometry control were a full-time endeavor. Given the total bridge length (1,036 feet), longitudinal jacking operations were designed to mitigate the long-term effects of creep and shrinkage. A single bridge instead of twin bridges eliminated a major traffic shift and complete cross-over section, resulting in less opportunity for accidents during construction.

Concrete segmental bridges as a structure type are inherently durable due to sustainable materials, and the use of post-tensioned concrete, particularly as it is incorporated into the deck to prevent cracking. The concrete mix was enhanced to provide a durable structure, while still providing chloride penetration resistance. In addition to providing a high-quality, durable structure, future maintenance and rehabilitation costs were minimized by providing a segmental box girder bridge with quality materials and enhanced corrosion resistance details. For example, low permeability concrete was used for pier and footing concrete and calcium nitrite was added to provide additional protection against chloride protection, increasing the design life to at least 150 years. 

The single bridge provides a smaller overall footprint, fewer footings, and abutments; requiring less erosion control and fewer areas of environmental impact during construction.The focal point of the bridge are the two “quad wall” piers which represent stone trees emerging from the ground and supporting the arching concrete spans. The quad wall piers are comprised of four concrete columns that each curve outward in two directions symmetrically. The three dimensional design and detailing of the columns was very complex with a constantly changing cross section and reinforcing patterns. Workshops were held with the designer, contractor, reinforcing fabricator and form work provider to ensure all details were considered and to provide the most efficient design. The quad wall system of the piers provides stability and allowed for the balanced cantilever segmental construction of the bridge superstructure to be constructed from above, without temporary props in the river, minimizing impacts to all.

Project Details

Location:

Interstate 91, Brattleboro, Vermont

Owner:

Vermont Department of Transportation

Engineer:

Figg Bridge Engineers, Inc.

Construction Management:

PCL Civil Constructors, Inc.

Contractor:

PCL Civil Constructors, Inc.

Concrete Contractor:

Carroll Concrete Co.

Reinforcing Bar Fabricator:

Dimension Fabricators

Rebar Placer:

D.T. read Steel Co., Inc.

Project Cost:

$60 Million

Reinforcing Tons:

1,872

Total Concrete Yards:

18,058

Rebar Producer:

Evraz, Inc. / Keystone Steel & Wire / CMC Steel / Nucor Steel / Gerdau / North American Stainless