View of the construction site on May 30, 2012. Photo courtesy of Checkeredhousebridge.com
RICHMOND, Vt. (AP) After more than a year of planning using computers, laser levels and measuring devices accurate to a fraction of a millimeter, it took engineers with tape measures and construction workers with sledgehammers to finally bring the 83-year-old Checkered House Bridge into the 21st century.
On June 18, workers cut the historic 350-ft. (106 m) U.S. Route 2 bridge in two lengthwise by unbolting the braces holding the trusses together and began the process of pushing the sides apart to widen the span by 12-1/2 ft. (3.8 m).
As far as anyone involved in the project has been able to determine, it’s the first time such a technique has been tried on such a large bridge. Officials say the wider bridge is needed to accommodate modern traffic that frequently includes bicyclists, pedestrians and farm equipment. The span is scheduled to reopen a year from now.
Despite the preparations, the hardest push was the first. After workers moved one 300,000-lb. (136,078 kg) truss about 2 in. (5 cm) downstream on the Winooski River, crews spent hours trying to free a single spot at the base of the bridge where, despite the specialized rollers it was laid on and pressure from hydraulic jacks, it remained stuck.
“I’m really not surprised. It’s such a large structure and such an old structure that there have to be points, friction points, that it hangs up on,” said Dale Gozalkowski, of the Albany, N.Y.-based engineer firm Clough Harbour & Associates, who helped design the project and watched June 18 as it was put into action.
The original 350-ft. Pennsylvania truss bridge was built in 1929, two years after an epic flood washed out a covered bridge in the same spot. The bridges are marked by the crisscrossing I-beams that form a latticework, creating a steel canopy above the road surface.
Vermont Transportation Agency officials have known for decades that the aging bridge about 10 mi. east of Burlington needed to be upgraded or replaced. The travel surface was 20 ft. (6.1 m) wide, barely wide enough for two vehicles to pass each other, and the aging steel and the road surface was deteriorating.
For years, Vermont officials debated the best course of action. They considered tearing it down and building a new one, leaving it alone or turning it into a one-lane bridge and building another alongside it. But the bridge is the last of its kind in Vermont on a major roadway and, as such, is historically significant, said Scott Newman, the historic preservation officer of the Vermont Agency of Transportation.
The total project cost for the bridge and the approaches on both sides is about $16 million. A new open bridge could have been built for about $7 million. But the federal law required that the historic bridge be preserved, if possible, Newman said.
“Folks are always looking at the bottom line and I don’t blame them. We are very conscious of the bottom line,” Newman said. “These are truly unique circumstances where you have a big structure that is highly significant where we need to be in compliance with federal regulations.”
But Vermont Transportation Secretary Brian Searles said June 18 that the price comparison didn’t take into account the design-build system used for the Checkered House Bridge.
“One cannot discount the engineering significance of what is being accomplished this week in Richmond,” Searles said. “It is a truly innovative undertaking that will preserve what is believed to be a valuable historic resource.”
Once the decision to preserve the bridge was made, it became an engineering challenge.
“This is not something you see in a textbook every day,” Jerry Pfunter, of the Tallahassee, Fla.,-based Finley Engineering Group, which was contracted for the actual widening of the bridge. “Typically, we start with a clean slate; we’ve got new members; we can build the traditional connections. Here we have a situation where we are partially taking apart connections.”
After the two sides were separated, workers used tape measures to note the progress.
At several points on the bridge, the workers reported by radio the progress of the separation in inches and fractions of inches. On one end of the bridge, an old-fashioned 4-ft. level was clamped onto the side of the bridge to provide an instant readout of whether the bridge truss was perfectly vertical.
Later, the truss had gotten stuck a second time, although the truss was completely separated, and it appeared doubtful that crews would be able to make the push in one day.