Design Has Helped to Protect Span, Expert Says

SOURCE: The Poughkeepsie Journal · POSTED: 08/10/08

Despite falling into disuse for more than 30 years, the Poughkeepsie Railroad Bridge has largely maintained itself, inspectors said.

On May 8, 1974, a fire broke out on the bridge. The blaze marked the end of the span as a train bridge. In the decades since, the design of the bridge has helped protect it from the environment.

"We determined that the condition has not changed much at all since 1969," said Peter Melewski, principal at the architecture, engineering and planning firm of Bergmann Associates, which oversaw the physical inspection of the structure.

The inspection process, subcontracted to the McLaren Engineering Group of West Nyack, took place in fall 2007. The previous significant inspection was in 1980, Melewski said, and not much had changed in the 27-year interim.

"The majority of the bridge ... has gotten a mild coating of rust, and that rust is protecting it from additional moisture getting to the steel," Melewski said. "It wasn't designed that way; it just happened to work out that way."

Melewski said the bridge design leaves relatively few places for snow and rainwater to accumulate, further reducing the opportunity for corrosion. Walkway Over the Hudson will soon begin a $4.1 million project to replace rivets and steel at points throughout the bridge.

Some Deficiencies Found

The most significant deficiencies inspectors found were in the outside chambers of two underwater wooden caissons, each of which had a void about 50 feet long. During the original construction, these chambers, known as weighting pockets, were filled with rocks to sink the caissons to the bottom of the river bed.

Sonar imaging was used to examine the interior of the caissons as part of a series of inspections.

"We could see the inner chamber wall was solid and intact, and just due to the massive size of the caissons, there's more than ample capacity left in those piers for its intended use," Melewski said.

He said the caissons will have to be repaired in the future, but are strong enough to support the bridge for deck work and public use.

The bridge was built to hold 11,350 pounds per foot for train engines and 6,000 pounds per foot for train cars.

When the caissons are repaired, Melewski said, all work will be done above the river's bed, meaning no soil will have to be disturbed. Because almost all the other necessary work would be to build the walkway itself on the deck and access points on both ends of the bridge, there will be virtually no environmental impact on the river, Melewski said.

"Ninety-nine percent of what's going on in this project is happening 200 feet in the air," Melewski said.