Wind an obstacle during installation of Milford footbridge
MILFORD – For a short time Friday morning, Milford had a 60,000-pound swinging bridge over the Souhegan River.
It happened about 10:30 a.m., as 30,000 pounds of steel, hanging from a crane at Keyes Field, and another 30,000 pounds of steel, hanging from a crane near the Boys & Girls Club on the north bank of the river, were about to get bolted together. Suddenly the wind struck.
“It got up to 40 (mph). That’s a little strong,” said Sean Coffin of Moore’s Crane Service of Dover, operating the monstrous crane at Keyes that held one of the 75-foot-long spans over the river.
The pedestrian bridge is part of a half-million-dollar, federally funded project to connect the banks of the river a half-mile west of the Oval. The two halves were built in Indiana and trucked to Milford for the Friday morning installation.
In theory, Friday’s installation was straightforward – pick up each half of the bridge with a crane and suspend them over the river, end to end; bolt the outer end of each span into concrete abutments; then bolt the inner ends together to create a 150-foot-long walkway.
The fact that each span weighs more than a dozen elephants didn’t seem much of a problem to the half-dozen men working for PRB Construction of Gilford, whose past experience included skyscrapers and automobile bridges.
“It’s not that heavy. It’s heavy, don’t get me wrong, but we’ve done more,” Ralph Bruce said of a span, as it dangled from steel cables and nylon straps.
Then the wind came, bringing midmorning bursts that downed a couple of power lines in town and peppered the river with tree debris.
Coffin knows how fast the wind blew because his crane’s high-tech controls – it is operated with a couple of joysticks, like a giant video game – include data from a wind-speed gauge at the tip of the boom, almost 80 feet above the Souhegan River at the time.
The gauge is there for a very good reason, said Coffin: “These things can tip over if it’s too windy.”
That seems hard to believe, considering that the $1.4 million crane weighs 150,000 pounds and had another 150,000 pounds of counter-weights on it. But Coffin, holding a thick book full of cautions from the manufacturer, pointed out that holding half a steel bridge above a river creates a lot of destabilizing leverage.
Despite the gusts, neither crane appeared to wobble. The suspended halves of the bridge were another story.
As riggers Jeff Morgan and Tim Goodheart tried to hook splice plates from one span into alignment holes on the other span, the two sides swung back and forth, moving six feet or more.
For a time, things looked almost alarming. On the riverbank, engineers Matthew Low and Josif Bicja, who designed the installation, watched carefully.
But after about 15 minutes, the two spans were connected and the laborious process of installing 64 bolts began.
“Nobody got seasick,” joked Paul Blandford, president of PRB Construction.
By noontime, the bridge was done – and suddenly going from Milford Lumber on Route 13 north to Elm Chiropractic Center on Elm Street was a three-minute stroll instead of a 20-minute hike.
“This has been a good job,” said Low, who works for Hoyle, Tanner & Associates of Manchester. “The town is really excited about this; that makes it a lot more fun for us.”
The biggest difficulty, he said, was fitting the installation between the tennis courts at Keyes Field and high-power lines running next to the new Boys & Girls Club on the north side of the river.
The bridge is rust-colored, and for a very good reason: It is already rusty. The spans are made of “weathering steel” that quickly oxidizes, creating a thin coat of stable rust that should prevent damaging rust from getting through without the use of paint.
“The only maintenance the town should have to do is on the pressure-treated wood deck,” said Low.
The bridge was bought as part of a $500,000 grant from the federal Department of Housing and Urban Development, which will also build a walking trail on the north side of the river, connecting the new bridge to Emerson Park and Route 13, as well as various improvements around the Oval.
Ironically for the workers who were swaying in the wind, they weren’t on Milford’s only swinging pedestrian bridge. On the east side of the Oval, the so-called Swing Bridge was first built in 1854 to help people get to jobs in local textile mills, and still links people on Amherst Street with the downtown.