The U.S. Navy now is
testing a $2-million modular hybrid pier section in San Diego
that may provide an inexpensive and long-range solution to its
berthing needs. The precast, lightweight concrete structure
requires few piles and can support 140-ton mobile cranes.
Developed by Berger/Abam Engineers
Inc. Federal Way, Wash., the 50-ft by 100-ft section is a
test for a new 1,300-ft-long floating, double-decked pier,
dubbed MHP. It was constructed over eight months in nearby
Tacoma by Concrete Technology Corp. for the Naval Facilities
Engineering Service Center. The pier is intended to be repair-free
for 100 years, twice as long as a typical pier.
High. Floating, modular, concrete pier section
made 1,200-mile trip without mishap. (Photos above and
below courtesy of Berger/Abam Engineers)
Virtually every detail found in
the larger pier was incorporated in the test section. It was
towed 1,200 miles to San Diego in mid-September for tests
of fendering, bollards, deck capacity and mooring system.
"The MHP concept promises to reduce the ownership costs
to the Navy of its waterfront infrastructure while enhancing
ship support," says Preston S. Springston, NFESCs
MHP project manager. "Construction and ocean tow delivery
of the MHP test bed is a significant step forward in the Navys
ongoing evaluation of the readiness of mod-ular, floating
structure technology for implementation as general purpose
Bed. Pier section has all features of a full pier.
The test bed is comprised of two
50-ft-square segments joined by 14 each, 1 3Ú8-in.
DYWIDAG bars. It uses high-strength lightweight concrete to
eliminate reliability concerns over aggregate and incorporates
two mats of rebarstainless steel in the exterior walls,
keel and deck and epoxy-coated in the interior for one section
and MMFX (2), a proprietary corrosion-resistant reinforcing
steel in the other. On both sections, the haunched 9-in. thick
walls are precast and the keel is cast-in-place. The two decks,
service and top, are comprised of precast panels with 6-in.
to 8-in. poured-in-place overlays. Walls and decks are post-tensioned
for durability and strength.
"The MMFX (2) [rebar] is less
costly but we needed to determine the amount of corrosion
protection it provides so were testing the two [kinds]
side by side," says Michael W. LaNier, Berger/Abam executive
vice president. The firm selected high-strength concrete after
first testing carbon-fiber reinforced concrete. "While
the carbon reinforcement functioned as expected, it was more
costly," says LaNier.
The pier and tied-off ships will
float with the tide. The full pier will be anchored on two
to four pile caps, depending on wind conditions. The tremie
cast caps will sit on eight, 80-ft to 100-ft long, 24-in.
dia driven precast concrete piles. Each pile cap provides
footing for a 46-ft long, five-ft sq hollow stainless steel
mooring shaft buffered by four large rubber fenders, which
allow the pier to ride up and down with the tide and dampen
berthing and seismic forces.
The lower service deck houses all
utilities. MHP can service all ships except carriers. Constructing
a new pier would cost about $45 million and could be installed
in less that six months, including demolition of an existing
pier. "It is faster to install, causes less environmental
disruption and can be moved," says LaNier. To move it,
workers unbolt the bottom 5-ft footing of the mooring shaft
and float the structure free to another pier cap.
Displacement of the test section
is 1,770 long tons and the full pier would be about 46,240
long tons or about five times more than a destroyer. Because
the shaft penetrates both decks, another 12-ft section can
be bolted on top in storm surge conditions.
The Navy has about 500 piers and
wharves in the U.S. and 75% of them are over 40 years years
old. The next step is to construct the 1,300-ft long by 88-ft
wide pier, which will be assembled in four, 325-ft long segments
at a site yet to be determined. "The project goal is
to prove out the technology by mid-2006 and enable construction
by 2007," says Springston. Expected life-cycle savings
for the pier is $15 million.