Precast segmental bridges had been built in New England before, but each time a job specific fabrication plant had been setup on the project site. In 1997, Unistress decided to change all that, and our opportunity lay 150 miles to the east.
The Central Artery/Tunnel project in Boston, a massive undertaking by the Massachusetts Turnpike Authority to decongest five major highway interchanges and depress an elevated traffic artery running through the heart of downtown, intended to build a majority of these interchanges and elevated roadway sections using precast segmental box girders. The trapezoidal box shape presented many structural advantages and was determined to be the most desirable aesthetically for this urban area.
Having risen to challenges in the past and knowing growth only comes through the assumption of some risk; Unistress presented our proposal to the successful contractor. Our state-of-the-art production facility was shown to be fully capable of fabricating the high quality precast concrete units required, eliminating the need to set up a temporary facility in the heavily congested downtown Boston area. Our knowledge and equipment to safely transport the finished segments to the jobsite sealed the deal. Thus, Unistress became the first New England precaster to fabricate segmental bridge units offsite for shipment to the project location.
Since winning that first contract in 1997, Unistress has cast more than 1,500 segments under two contracts for the I-90/I-93 interchange. Approximately 200 segments are included in our third contract currently in production, and an additional 510 segments will be produced under our newest contract.
Box girder sections range from 7 to 10 feet in depth, up to 11 feet in length, 42 feet in width and weigh as much as 70 tons. They are designed for both span-by-span and balanced cantilever construction techniques, dependent on the location of the specific span. Truck shipments from the Unistress plant in Pittsfield, MA are generally scheduled for early morning deliveries due to the large size of the elements. The sections essentially travel the entire length of the Massachusetts Turnpike (I-90), starting at the western end and ending at the project site in Boston, I-90's interchange with I-93.
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