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.
|Riding 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 berthing piers."
|Test 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.he 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.