Temporary Spans End Up As Anything But Lightweight.

ENR 

What started out to be a five-year temporary bridge has become one of the heaviest and longest of its kind, slated to carry traffic over the Fore River in Massachusetts for 15 years once it is opened next year.

Middlesex Cos., Littleton, Mass., is nearing completion of its three-year, $78-million contract to build twin panel bridges between Quincy and Weymouth over a shipping channel used by large oil tankers. The bridges will replace an old bascule bridge - originally set for rehabilitation - that was straining under a traffic load of some 50,000 vehicles a day.

"The project started out as a detour bridge while they reconstructed the bascule spans," say William Killeen, president of Acrow Corp., Carlsdadt, N.J., the supplier of the panel bridges. But when designer Hardesty & Hanover, New York City, determined that the bascule bridge needed to be replaced rather than rehabilitated, the Massachusetts Highway Dept., asked for a temporary bridge that would last 15 years instead of five.

As a result , the twin two-panel bridges weigh 10,000 tons with 210-ft vertical lift spans and a total length of 2,500 ft. says Killeen. "Physically, there are no longer (temporary) bridges in existence, but not as much tonnage of steel," he says. The bridges are being built just 50 ft. from the bascule structure.

Middlesex drove 180-ft-long pipe piles of 24 in. in diameter to 150 ft. into the riverbed for the center piers, says Jeff Roig, Middlesex project manager. The 22 approach spans rest on piles, driven as deep as 160 ft. Segments were preassembled in New Jersey and barged to the site. There, crews used up to 600-ton cranes to lift them into place, up to 200-ft. above the waterline. Spans include 10,000 panel pins and 60,000 structural bolts. Tolerances are less than a quarter inch, say Roig.

The 250-ton center-lift spans will have a 170-ft. vertical clearance, notes Killeen. To erect them, Middlesex requested four week-long closure periods a year in advance. The Coast Guard allowed them six periods, says Roig.

While crews hoisted the spans into place, workers lifted the spans 5 ft. several times to test the lifting and electrical systems before hoisting them up to full height. "This is the largest lift span any of us have worked with, says Roig.