Category Archives: Bridge Engineering

The 10 Longest Floating Bridges in the World

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Lacey V. Murrow Memorial Bridge, Seattle, U.S.A, 2,020 meters, 1940. The bridge carries the eastbound lanes of Interstate 90 across Lake Washington from Seattle to Mercer Island, Wash. The world’s first floating bridge to be built using concrete pontoons, it was designed by engineer Homer Hadley, and constructed by the Puget Sound Bridge and Dredging Co., at a price tag of $9 million. While undergoing reconstruction in 1990, an 850-m-long section of the bridge sank when a storm filled one pontoon. The rebuilt bridge reopened in 1993, at a cost of $93 million.
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Hood Canal Bridge, U.S.A, 1,988 meters, 1961. The bridge carries State Route 104 across Hood Canal, a natural fjord that empties into Puget Sound. The bridge connects the Olympic and Kitsap Peninsulas. The water depth at the site ranges from 24 to 104 m, with several hundred feet of mud below, which made construction of support columns for conventional bridges too costly. A windstorm in 1970 caused some of the pontoons to break loose from their moorings and sink. The bridge was rebuilt and resumed operation in 1982. Between 2003 and 2009, the Washington State Dept. of Transportation replaced the eastern half of bridge’s floating section, the east and west approach spans, the east and west transition spans, and the west- half electrical system. Fourteen pontoons were fabricated at Concrete Technology in  Tacoma. Each pontoon has about 40 individual cells.
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Demerara Harbour Bridge, Guyana, 1815 meters, 1978. The bridge spans the mouth of the Demerara River at Guyana’s capital, Georgetown. Thos. Storey(Engineers) Ltd., a British firm known for manufacturing Bailey Bridges, designed and also fabricated the bridge components. Guyana’s Ministry of Works and Transport designed the abutments, toll plaza and western approach road. The two- lane bridge currently carries an average of 14,000 vehicles per day. The bridge’s capacity is limited by having to open daily to allow river traffic to pass, and the retraction process is slow. Also, bridge opening times depend on water levels and flow velocities (tide), which often conflict with peak traffic times. The Demerara Harbour Bridge Corp., the bridge’s owner- operator, hired LievenseCSO, a Dutch hydraulic and coastal engineering firm, to conduct a feasibility study and design for a new Demerara River Crossing. Their report, issued in August, 2017, states that the exisitng bridge “has long passed its technical lifetime” and “is no longer able to service the present and future traffic demand.” It recommended the construction of a new three – lane bridge with fixed footings.
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Homer M. Hadley Memorial Bridge, U.S.A., 1,772 meters, 1989. It carries the westbound and reversible lanes of Interstate 90 across Lake Washington  between Mercer Island, Wash., and Seattle. The construction cost was $97 million. It is named for Homer Hadley, the engineer who designed the bridge’s companion span, the Lacey V. Memorial Bridge. It features 18 pontoons: 10 concrete and nine with elevated superstructure.

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Berbice Bridge, Guyana, 1,571 meters, 2008. The bridge spans the mouth of the Berbice River and features 39 pontoons. It was built by the consortium of Bosch Rexroth and Mabey & Johnson. The construction cost was $38 million. It opens for river traffic for 1½ hours each day. Cars pay atoll of 2,200 Guyanese dollars.(U.S. $10)
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Nordhordland Bridge, Norway, 1,246 meters (pontoon section), 1994. This combined cable- stayed and pontoon bridge near the city of Bergen connects the mainland and the island of flat, spanning Salhusfjorden, which is 500m deep. It carries two lanes for cars and a pedestrian / bicycle path. The floating section is a steel box girder on top of 10 concrete pontoons, each with nine watertight cells. It was designed by AasJakobsen. Given the fjord’s extreme depth, lateral anchorage systems would have  been too expensive. Instead, the pontoons are fastened with flexible plate connections liked by bolts and cables under tension. It was built by a consortium, Arbeidsfellesskapet Salhus Bru, made up of Norwegian Contractors, Aker Enterprenor, Veidekke and Kvaerner Eureka.
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Bergsoysund Bridge, Norway, 933 meters, 1992.  The bridge connects the islands of Aspoya and Bergsoya, spanning a fjord with a water depth of 320 meters. The engineering firm Johns. Holt designed the pontoons and abutments, and DNV Veritec designed the steel superstructure. Norwegian Contractors built the concrete pontoons, and Akeer Verdal built the steel pipe truss superstructure . It rests on seven concrete pontoon foundations.
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William R. Bennett Bridge, British Columbia, Canada, 690 meters, 2008. SNC – Lavalin handled the design and construction and received a contract to operate and maintain the bridge for 30 years, as a public- private partnership. Buckland & Taylor Ltd. Were the lead design firm, in partnership with SNC-Lavalin. The five- lane bridge on nine pontoons, all of them 25m wide, and ranging in length from 25 m to 90 m. The construction cost was 144.5 million Canadian Enter a caption
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Yumemeai Bridge, Osaka, Japan, 410 meters. The world’s first floating swing bridge, it connects two artificial islands, Yumeshima and Maishima, in Osaka Bay. A floating bridge design was chosen because the soft ground of the reclaimed land was more suited to this approach. The bridge’s double arches rest on two large steel pontoons. The pontoons were designed to resist corrosion by lining their sides with titanium plates as well as a cathodic protection system. The floating portion of the bridge weighs 30,000 tons. The North Waterway which it crosses is rarely used by boats, but when it is, the bridge is maneuvered by tugboats.

Evergreen Point Floating Bridge, Seattle, U.S.A
Evergreen Point Floating Bridge, floating portion is 2,350 meters. It was completed in 2016. The six- lane bridge carries State Route 520 across Lake Washington from Seattle to its eastern suburbs. It features 77 concrete pontoons secured to the lake bottom by 58 anchors tethered to steel cables. Twenty- one of the pontoons that support the deck and superstructure are each 110 m x 23 m x 8.5 m and weigh 10,000 tonnes. Fifty- four supplemental pontoons used to stabilize the weight of the bridge weigh 2,300 tonnes each. Two cross pontoons weighing 9,200 tonnes each at each end connect the deck to the fixed bridge approaches using hinges. The Pontoons were designed by WSDOT and the superstructure by KPFF. The bridge was built by a joint venture made up of Kiewit Corp., General Construction Co. and Manson Construction. The lake’s topography- a water depth of 61 m of soft silt- favored the choice of a floating bridge, as a conventional bridge would be prohibitively expensive and require costly towers and huge approaches that would be out of character with the largely residential area. The construction cost was $4.5 billion. It replaced the previous Evergreen Point Floating Bridge, A four- lane span that opened in 1963.