A bridge to last 100 years

Carrara made the enormous beams in a giant 270-feet-long casting bed at its Addison County facility. The beams include spaces for the cabling ducts where high-strength cables-called post-tensioning cable-are eventually pulled through and then "stressed" to 44,000 pounds of tension with the aid of a jack-and-chuck system.

When completed, the individual beams will be "joined" together, at the joints, to simulate a much longer concrete structure. The bridge's approach spans measure 120 feet making the entire simulated structure 480 feet in length-quite a structure even by ancient Roman engineering standards.

When an 8-inch thick concrete overdeck is added, the project will be ready to support traffic sometime during September 2010.

"We'll perform the wire tensioning at the site before the winter sets in," Weigand said. "And when the tensioning process is completed, we will fill the ducts with grout over several days."

Regarding the sorry condition of the now doomed Lake Champlain Bridge, Weigand said a lot of the problems stem with non-reinforced concrete piers as well as neglect.

"There have been advancements in concrete production between the 1920s, when the closed lake bridge was built, and today. With non-reinforced concrete as you see in that bridge, loads and stresses cause serious cracks; the underwater environment takes its toll, too. The old structure can't hold itself together," he said. "But with a reinforced concrete structure, you have the same loads and stresses, but the material is bound together making it more durable, more flexible, if you will."

I wondered out loud about the April 2002 Champlain Valley Earthquake which seriously damaged portions of N.Y. Route 9N and cracked chimneys on both sides of the lake. Did the earthquake hasten the demise of the Lake Champlain Bridge?

"I can't say," said Weigand.

But I think he knows that the lake bridge had been neglected by its so-called stewards. Perhaps he was being too polite to call attention to the fact?

When I asked Weigand how long the Middlebury bridge will last, the engineer smiled. "There's no reason why the new bridge shouldn't last 100 years," he said. "Of course it will depend on wear and tear-and proper maintenance."

Let's hope that future stewards of the Cross Street Bridge will do a better job than the those who failed to keep an eye on the Lake Champlain Bridge.

And as an ancient Roman engineer might have said to wish a neighbor the best of health-Centum annus!

May you live 100 years.

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