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Tacoma Narrows Number Three | |
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Tacoma Narrows Number Three by ArchitectureWeek Does your project require special equipment to convey structural steel on site and into position? Maybe big trucks with oversize loads, and special cranes. But have you ever commissioned a flatbed ship for placing steel? That was the chosen approach, over the last year and a half, for on-site delivery of structural steel bridge modules for the third suspension span to make the historic Tacoma Narrows crossing. And for Dockwise, semi-submersible shipping specialists, delivering steel in the Tacoma Narrows with a Swan-class freighter probably counted as fairly easy duty. Special Delivery For the 2007 Tacoma Narrows project, the Dockwise Swan (alternating with sister ship the Teal) provided both transport from South Korea and installation staging of the bridge deck frame modules. This allowed the large open-truss units — more than four highway lanes wide, half-again longer, and 30 feet (9.1 meters) high, shaped to accommodate a second, lower traffic level in the future — to be precisely positioned for "unloading" by way of being winched with gantries directly into position in the bridge structure for installation (or to be shifted sideways by a dolly system, for module destinations the ship can't quite reach). Swan is a pretty special flatbed rig, with an overall length of 180.5 meters (592.2 feet), breadth of 32.26 meters (105.84 feet), depth of 13.30 meters (43.64 feet), and a gross tonnage of 22,788 metric tons (25,119 U.S. tons). She has a cargo deck area measuring 126.80 by 31.60 meters (416.01 by 103.67 feet), which allowed 15 or 16 of the deck frame sections to be carried at once, and she runs at a cruising speed of 14 knots for up to 65 days of continuous service, making regular work of the 11,000-mile (17,700-kilometer) round trip between fabricator and job site. >>> Discuss this article in the Architecture Forum...
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