Carolina Bridge Company Inc. Seven bridges were completely replaced in less than two months on an island that has no highway access from the North Carolina mainland.

An assembly line of construction crews worked like clockwork, around the clock, to replace seven bridges in 45 days on the island of Ocracoke, N.C. Thanks to precast components and careful logistics, Carolina Bridge Co. Inc., Orangeburg, S.C., earned a $350,000 bonus on its $8-million contract with the North Carolina Dept. of Transportation.

The residents of the island, a popular summer destination spot and national park, preferred the total closure of Highway 12 for a construction season rather than a more drawn-out reconstruction process, says Pablo Hernandez, NCDOT assistant resident engineer. The seven timber bridges, more than 50 years old, were functionally obsolete and needed widening from about 25 ft to 33 ft to provide for two lanes plus a shoulder, he says.

Although structurally sound, the creek crossings lacked curbs, barriers and other modern design elements, he says. Moreover, because timber is more flexible than concrete, the asphalt paving atop it “starts to pop up and peel off,” he says.

Carolina Bridge replaced the seven bridges with six precast bridges and one double-barrel aluminum culvert, says firm vice president Richard Nickel. The contract allowed for a 75-day road closure beginning Jan. 2, but six crews working non-stop replaced all the bridges in 45 days. The contractor received both the $250,000 bonus for finishing before March 15 and the maximum bonus of $10,000 a day up to 10 days before that. Liquidated damages would have been $10,000 a day after March 15.

Carolina Bridge Company Inc. Steel and concrete pilings replace timber to support precast concrete bridges.

The island is only accessible by water or air. All equipment, precast sections and materials were delivered on ferries and staged in three areas allowed by the National Park Service. With a three-mile work zone, crews functioned as if on an assembly line. “The pile-driving crew would use the existing bridge as a work platform,” says Hernandez. “The next crew installed the precast caps, and the next crew set the slabs.”

Florence Concrete Products Inc., Florence, S.C., precast pilings 20 ft long and 16 in. square, bolted onto 26.5-ft-long H-pile sections. Using a composite piling design eliminated the need to drive piles with high-pressure jets into dense sands, which would have been an environmental concern, says Hernandez.

Bayshore Concrete Products Corp., Cape Charles, Va., precast the superstructure slabs, each 3 ft wide, 21 in. deep and either 50 ft or 35 ft long, says Hernandez. Concrete barrier rail is cast directly onto the slabs as well. The new bridges range in length from 115 ft long to 250 ft.

Crews are finishing up paving, though the final wearing surface will probably have to wait for April and warmer weather, says Hernandez.