Boston, MA, November, 2012 -- The 1936 Fore River Bridge, a bascule bridge that fed nearly 40,000 vehicles daily into the greater Boston highway system and crossed a busy shipping and sail boat channel, is being replaced with a $280-million vertical lift bridge that will be one of the largest in the United States, designed by STV for the Massachusetts Department of Transportation.
The new vertical bridge, with airy steel towers, will widen the channel from its current 175 feet to 250 feet to better accommodate large tankers; and will increase the height of the bridge to 60 feet for sail boats and commercial boats that do not require bridge openings. When the vertical lift bridge is raised (approximately 500 times per year), the vertical clearance will climb to 175 feet, enough for most commercial ships.
“The choice of a vertical lift bridge was driven by the need for a wide channel,” said Mark Ennis, P.E., PMP, STV project director. “If we had chosen a bascule bridge spanning a 250-foot channel, it would have been the largest/heaviest in the nation, which would have carried some risk.” The severely deteriorated, older bascule bridge was demolished 10 years ago when it was replaced with a temporary bridge that is now approaching the end of its service life.
The new bridge will have four lanes for vehicles, bicycle lanes, and ADA-compliant sidewalks. It will be located on the site of the 1936 bridge and will be operated from a control tower that provides visibility to both the roadway and waterway.
The vertical lift portion of new bridge was designed to 60% and the approach span structures to 30% by the STV-led design team. MassDOT selected a Joint Venture of JF White and Skanska-Koch, supported by Parsons Transportation Group, to be the construction and engineering design-build team to complete the job by the end of 2016. The new bridge, which connects the cities of Weymouth and Qunicy, Massachusetts, has raised engineering, environmental, aesthetic and community challenges.
Engineering / Environmental Challenges
The 325-foot movable lift span is expected to be constructed elsewhere and be floated into its final position at the bridge site. It will be composed of steel through trusses (with trusses outside the sidewalks) and a lightweight concrete deck. Overall, the bridge represents a conservative, safe and long-lasting approach.
In addition to the lift span there are 1,000 feet of approach span structure, and 1,000 feet of earth support structure on either side of the river.
In constructing the underlying substructure, including the four 60-foot-deep concrete plinths (which run from the deck to the water and are supported by steel encased concrete drilled shafts), engineers will have to avoid the 1936 bridge’s still-existing pile foundations, as well as utility tunnels and electric lines. The bridge alignment must also steer clear of an MWRA deep rock tunnel, an old ship yard and an electric power plant in the vicinity of the new bridge.
Compounding the engineering challenges, “major silt producing activities”, such as dredging in the waterway, cannot occur between February 15th and September 15th in order to minimize impacts to winter flounder and diadromous fish during spawning, juvenile development, and migratory periods.
The foundation plinths, which will hold up the towers, are made of concrete, but will be formed and stained to look like granite and have joints to simulate the look of large blocks. Portions of the towers (the tops and the sides facing the river) will be clad in a fine, stainless steel mesh, a design innovation that makes the towers appear lighter and obscures the stairways, elevators and utility conduits.
STV and the Mass DOT met 16 times over two years with the public and with a variety of community and local government groups to discuss the design and construction process, traffic issues and aesthetics. This interactive process played a major role in establishing many of the key features in the appearance of the bridge.
STV is celebrating its 100th anniversary in 2012. Since its earliest predecessor firm opened its doors in 1912, the firm has grown to become a leader in providing planning, architectural, engineering, environmental, and construction management services for buildings and facilities, transportation systems, energy and infrastructure. STV is ranked 32nd in Engineering News-Record’s Top 500 Design Firms survey. STV is 100 percent employee-owned. For more information, visit our website at www.stvinc.com or follow @STVGroup on Twitter