Barge Builds Boston's Big Box Bridge

A Flexifloat crane barge was the key to building the Storrow Drive Bridge over Boston's Charles River.

Mounted on the barge's deck, a Manitowoc 4100W crawler crane with a Ringer attachment was used to lift and set the bridge's massive box girder segments.

The Storrow Drive bridge has three spans totaling 830 feet in length. The bridge's 76-foot roadway will accommodate four lanes of traffic and is carried by a continuous, variable-depth composite steel box girder with cantilevered floor beams. The trapezoidal box girder measures almost 35 feet wide at the top flange and is 18 feet deep at the main piers. It is one of the largest steel box girders in North America.

General contractor Daniel O'Connell's Sons, Inc. of Holyoke, Massachusetts constructed the bridge as part of the city's $7.7 billion Central Artery Project. O'Connell's engineers determined that placement of the over-water girder sections could best be accomplished using a 300-ton capacity Manitowoc Ringer crane mounted on a barge. However, the narrow 40-foot wide locks at the Charles River Dam precluded access to the site by conventional barges of sufficient size to safely support and work the 788,000-pound machine. To gain the needed barge access, the contractor called on Robishaw Engineering for assistance.

For this application, we designed and proposed a Flexifloat Series S-70 assembly comprised of 18 Quadrafloats and 13 Duofloats. These modules were trucked around the narrow locks to the construction site on the Charles River, offloaded and assembled in the water into a 110-foot by 110-foot "T"-shaped assembly. This arrangement provided adequate buoyancy and structural capacity to support a total deck load of over 1.5 million pounds. Configuring the modules into a "T"-shaped assembly permitted the center pin of the machine to be positioned within 48 feet of the edge of the hull while retaining excellent barge stability under all anticipated load conditions. The design allowed the Manitowoc crane sufficient outboard reach to lift and accurately place the largest 194-ton bridge girder segment while maintaining a barge inclination of less than 2 degrees.

Daniel O'Connell's is the first of two Flexifloat barges used to support ringer cranes for the Boston Central Artery/Tunnel project.