Bridge design options divide DOT, local panel

BUCKSPORT – The team of state engineers and the local public advisory committee, or PAC, may find themselves at opposite ends of the bridge as they try to select a preferred option for the design for a new span over the Penobscot River.

The Maine Department of Transportation has put the new bridge project on a fast track after discovering extensive deterioration in the main cables of the existing Waldo-Hancock bridge between Prospect and Verona.

Transportation officials announced last week that now they hope to open the new span by July 1, 2005, in time for the tourist season that year.

Earlier this summer, the PAC had identified two styles of bridge for further consideration – another suspension bridge similar to the existing bridge, and a modern cable-stayed bridge similar to the new bridge in Boston.

At a meeting Monday night, however, DOT Project Manager Tom Doe expressed concerns about any suspension design that would use the same type of cable design as the existing bridge; while some PAC members had reservations about a cable-stayed bridge, which engineers acknowledged have had problems with corrosion in some of the cables.

“We know this [suspension bridge] will last 75 years,” PAC Chairman David Milan said. “We don’t know what the cable-stayed bridge’s life is going to be.”

PAC members raised questions about problems at the Sunshine Skyway bridge and other cable-stayed bridges, specifically problems with corrosion that forced the Florida Department of Transportation to repair sections of the bridge, including one cable that failed.

Waldo County Commissioner John Hyk, a PAC member, pointed to reports from the Florida department noting that some of the cables are encased in concrete.

“They’re in the same situation we’re in here;” he said, “they can’t inspect that cable.”

There have been corrosion problems in cable-stayed bridges, especially in earlier designs, according to Denny Pate, an engineer with Figg Engineering Group, which has been hired to design the new bridge, and also designed the Skyway Bridge.

Although the design is an approved style of bridge, Pate said, it is “maintenance intensive.”

“It is difficult to inspect and difficult to assess with great accuracy with the cables buried in there,” Pate said.

He added, however, that new technology is being developed to monitor cables inside the concrete.

Figg also has developed new technology for cable stayed bridges including using external cables that are not buried in concrete, and a cable design that allows crews to remove and inspect individual wires in a cable and to replace them if necessary, without disrupting traffic on a bridge. The company has used that technology in one of its more recent bridges.

Committee members were not all convinced and requested more information about the cable-stayed bridges, including a life-cycle cost analysis on cable-stayed bridges and more information on monitoring systems. They also requested a copy of an owner’s manual for a cable-stayed bridge, which Figg President Linda Figg said their company provides with each of their bridges detailing maintenance and inspection procedures.

Some members showed interest in pursuing another suspension bridge, particularly after reading a report from HNTB Corp., an architectural engineering firm based in Kansas City, Mo., which indicated that such a bridge could be constructed within the timetable set by the department.

Project Manager Doe stressed that the report based its assumptions on using the same type of helically wound cable used in the existing bridge. That would put the DOT in the same position it is in with the existing bridge with “a cable that you can’t maintain,” he said.

Developing different technology would take time, Doe added, and could add as much as a year to the construction project.

Some committee members turned up their noses at the abundance of concrete bridges highlighted by Figg and asked the company for more information about steel structures or hybrid, concrete and steel bridges similar to the Zakim Bunker Hill Bridge in Boston, on which Figg worked.

Doe and the Figg team will field other questions from committee members during the week, and the committee is scheduled to meet again next Monday. At that time, they may be ready to make a recommendation on a style of bridge and the fate of the existing bridge, and also may discuss possible names for the new bridge.