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Segmental
Precast Floating Draw Span
The Need
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In order to make the Ford
Island as the site of new housing and administrative facilities for U.S. Navy's Pearl
Harbor Naval Base Hawaii, the Navy preferred a low profile bridge to the island that would
not obscure the setting of memorial and the experience of its many visitors, while at the
same time providing a convenient vehicle crossing. Although the traffic of large ships is
infrequent, only a few times a year, the bridge should provide a wide navigation
channel that allows the large ships to travel around Ford Island. |
The floating section of Admiral Clarey Bridge is being retracted under fixed bridge span.
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The Technology
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To meet the requirements, the
Navy built a bridge which was named after a decorated World War II submarine commander,
Admiral Bernard "Chick" Clarey. The prime designer of the bridge was Parsons
Brinckerhoff Quade & Douglas, Inc. and the contractor was a joint venture
Dillingham-Manson. The Admiral Clarey
Bridge, includes a 100 ft long causeway, a 400 ft long fixed trestle and a 1035 ft long
moveable section that includes the transition and floating drawspan. The fixed spans
include a low level section as well as a high level section to allow a small boat channel.
As the small boat channel is the high point of the bridge, it is also the location of the
control house for moveable span. |
Assembly of precast components of pontoon.
Pontoon under tow to Hawaii
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The moveable span is designed to be opened or closed within a 25-minute period. This is
accomplished by stopping traffic with traffic lights and lowering traffic gates, backed up
by traffic barrier gates. The two transition spans are then raised hydraulically and the
drawspan is withdrawn or extended using hydraulically powered winches. |
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The pontoon moves
through the water at a speed of 14 inches per second. When withdrawn, the pontoon slides
under six of the fixed approach spans, and for those spans, straddle type pier bents with
transversely post-tensioned caps are used. The drawspan is made up of three 310 ft long floating concrete modules,
bolted together to provide a 930 long unit. The pontoon modules were constructed using a
mixture of precast and cast-in-place concrete. each module is divided into 21 watertight
cells by longitudinal and transverse bulkheads. The pontoon walls and diaphragms are
precast and the reminder of the pontoon is made of cast-in-place concrete. Pontoons were
produced in Concrete Technology Corporation, Tacoma, Washington, and integrated at the
site into one continuos floating bridge pontoon. |
The Benefits
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- The Admiral Clarey Bridge, a low profile
bridge, reserves views of the historic harbor while, with its floating drawspan,
permitting the passage of large ships.
- Floating structures, with a modular and
repetitive configuration, provide the classic precasting opportunity for multiple reuses
of the concrete formwork. This will reduce forming costs, produce nearly identical
finished pieces, smooth surfaces, and easy fit-up and assembly.
- The method of combining precast and
cast-in-place techniques allows an opportunity to compress the construction schedule.
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Status
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The Admiral Clarey Bridge is
one of the five floating bridges in the world. Concrete Technology Corporation, as the
precast concrete manufacturer for pontoons in this bridge project, has been built several
floating structures since 1976 and the structures have been used as barge loading docks,
ferry terminals, break-waters, floating dolphins, boathouses, fuel floats, bridge and
sinkable caisson. The construction of floats has been variously hollow or foam filled,
cast in place or precast segmental, and post-tensioned or conventionally reinforced.
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Barriers
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For a busy navigation channel,
the operation of floating drawspan could be uneconomic since the opening or closing time
of this moveable span is considerably too long (25 minutes for 650 feet). |
Points of Contact
- Michael J. Abrahams, Senior Vice President,
Parson Brinckerhoff, One Penn Plaza, New York, NY 10119, Phone: (212) 465-5185, Fax: (212)
465-5575, Email: abrahams@pbworld.com.
- Gary Wilson, Marine & Heavy
Construction, Concrete Technology Corporation, Tacoma, Washington.
References
- 1999 Nova Award Nominations, The Nova Award,
Construction Innovation Forum, Inc., October 1998
- Precast Prestressed Segmental Floating
Drawspan for Admiral Clarey Bridge, PCI Journal, July/August 1998, Vol. 43, No. 4.
Disclaimer Statement
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Neither the Construction
Industry Institute nor Purdue University in any way endorses this
technology or represents
that the information presented can be relied upon without further investigation. |
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