It’s no secret that here at TheBridgeGuy, we’re into floating bridges in a big way. From Norway to Curaçao, it’s safe to say that we’ve covered a fair number of floating bridges on this site. And in this edition of TheBridgeGuy, not only am I off again in search of more cool bridges to write about, I’m in search of a floating bridge to write about. This time all the way to Pacific island of O’ahu.
Did you know that among the top 10 longest floating bridges in the world, only 4 are movable bridges? Well now you do.
Hood Canal, Demerara Harbour, Berbice and Yumemei rank as the third, fourth, sixth and tenth longest floating bridges in the world by overall length of their floating portions. But if we were to rank the longest floating bridges by their draw span lengths, the bridge with the longest draw span doesn’t even make the top ten for overall length.
That distinction goes to the Admiral Bernard “Chick” Clarey Bridge near Honolulu Hawaii, better known as the Ford Island Bridge. This draw span has a movable floating span of 930 feet, capable of creating a 650 foot wide channel for vessels entering or exiting Pearl Harbor. For comparison, the next largest (Hood Canal) is capable of opening to 600 feet.
In the middle of Pearl Harbor lies Ford Island, also known as Rabbit Island, Marin’s Island and Little Goats Island. The island changed hands several times over the years before becoming the property of Dr. Seth Porter Ford, the island’s namesake. After Ford’s death, it was sold and became a sugarcane plantation.
In 1916, the island was partially sold to the U.S. Army for use by the aviation division. In 1939, it became part of the U.S. Navy, where it was used as a base for battleship and submarine maintenance. It was the site of Battleship Row on December 7, 1941 during the attack on Pearl Harbor by Japan. During that attack, 21 naval vessels were either sunk or severely damaged, including the USS Arizona.
Access to the island is restricted to military personnel, their dependents and invited guests. The Navy operated two car ferries to the island for decades. The first went into service in 1961, with the second following in 1970. A number of foot ferries provided access to the island over the years. Today, Ford Island is part of Naval Station Pearl Harbor.
Proposals for a bridge between Ford Island and mainland O’ahu began as early as 1967, however none of the proposals gained traction due to cost. To fund the bridge, Senator Inouye of Hawaii proposed special legislation that would allow the Navy to sell land in order to fund the bridge project. The Manana storage site, 109 acres located in nearby Pearl City, was sold to the City of Honolulu for $94 million. An additional 34 acres on Ford Island were either leased or sold for private development to help sell the bridge idea to the public.
Linking the island with the mainland certainly helped spur development and give purpose to the bridge. The National Oceanic and Atmospheric Administration (NOAA) Pacific Tsunami Warning Center and the Pacific Aviation Museum were built on Ford Island as a direct result of the bridge being built. The bridge also connected the island more directly with the Kamehameha freeway nearby.
The bridge was built using the Design-Build contracting method. During the initial planning phase, Naval Facilities Engineering Command required that the bridge be low profile to avoid visual degradation to the nearby USS Arizona memorial and to maintain Ford Island’s historical and cultural value. This decision likely influenced the bridge type selected.
The Navy completed the environmental impact statement, which settled upon the fixed-floating bridge type, then short listed three design teams to complete proposals for the bridge. The final contract was awarded in August 1994 to a joint venture of Dillingham–Manson. Groundbreaking took place in January 1996 and the bridge was dedicated in April 1998.
The bridge is primarily a prestressed concrete girder design, founded on piers that sit on some 400 prestressed concrete piles. These piles are 24 inches in diameter and are driven 137 feet into the bottom of Pearl Harbor. The girders and deck panels used in the bridge were built at Concrete Technology Corporation in Tacoma, Washington and shipped by barge to O’ahu.
The 930 foot long floating portion is made of 3 individual pontoons that were then bolted together on site. Each pontoon is 310 feet long, 50 feet wide and 17 feet deep and were also built at Concrete Technology and towed to O’ahu. Based largely on the Hood Canal Bridge design, the floating portion is designed for 100 mph winds and 5 foot waves.
During an opening, the floating portion moves to the east – towards O’ahu. To accommodate the movable span, 36 straddle bents are used to create a pocket. Each bent is 60 feet wide and uses post-tensioning in the crossbeams.
Steel transition spans are used at each end of the movable span to connect the floating portion to the fixed portion. These transition spans can accommodate 1 foot of tidal variation (pitch) and 4.6 feet of transverse motion (yaw).
To operate the movable span, hydraulic cylinders are used to lift the transition spans off the floating portion. A pair of electric winches using 2 inch diameter cables are used to move the span. One winch pulls the draw open, while the other winch pays out. To close the span, the winch operation is reversed. The draw can open at 14 inches per second, with the entire opening taking 25 minutes from start to finish.
In the end, the bridge cost $78 million to build and came in both under budget and ahead of schedule. Besides military personnel and their families, tour buses cross the bridge daily. For those without military ID, the tour bus is the only way to access the Pacific Aviation Museum, the USS Missouri and other memorials on Ford Island. From the bridge you can see the USS Arizona memorial to the south as well as the impressive USS Missouri.
As the Executive Officer aboard the submarine USS Dolphin, then Lieutenant Bernard A. Clarey survived the attack on Pearl Harbor in 1941. Clarey would go on to a distinguished naval career, earning three Navy Crosses for valor, eventually rising to the rank of Admiral. His final assignment as a Navy Officer would be as Commander in Chief of the U.S. Pacific Fleet, returning him to Pearl Harbor in 1970. Clarey retired from the Navy in October 1973. He died at the age of 84 in Honolulu in 1996, while the bridge was under construction.
For further reading on the technical design of the bridge, check out this link.
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