A little wiggle room for bridge

Arrival of 100-ton deck expansion joint could mean delays for drivers

March 17, 2007 

A truck more than twice as long as a typical tractor-trailer is expected to deliver the first of two enormous expansion joints for the new Tacoma Narrows bridge Monday.

The 100-ton steel-and-neoprene joint, designed to fill the adjustable gap between the new bridge deck and the land, will be delivered to the bridge’s Gig Harbor anchorage on a 165-foot long semitrailer supported by 21 axles.

Tim Moore, senior bridge engineer at the State Department of Transportation, said the big truck – which has been on the road from Minnesota since March 1 – will take Interstate 90 across the Cascades, head south on Interstate 5 and lay over Sunday night at the Federal Way weigh station.

After Monday’s afternoon traffic rush, the truck will continue to Tacoma and head across the existing Narrows bridge, probably sometime between 8 and 10 p.m., Moore said.

Claudia Cornish, spokeswoman for the state’s Tacoma Narrows project office, warned that getting the 70-foot long expansion joint to the Gig Harbor anchorage might test the patience of drivers.

The truck and its load are 15 feet wide and will take up both westbound lanes while crossing the existing bridge.

Once it reaches the Gig Harbor side, the truck will leave Highway 16 at the 24th Street exit and make a left turn onto the 24th Street overpass, a tight maneuver that Cornish said could take as much as an hour to accomplish.

Traffic flaggers will help drivers get through the area during that turn, Cornish said.

The joints will help the steel bridge deck grow or shrink with changes in temperature. Combined, the two devices will be able to accommodate up to 56 inches of movement. There will be one at each end of the bridge.

The new bridge deck is 5,400 feet long at 65 degrees, according to Dave Climie, the Tacoma Narrows Constructors engineer who directed deck construction. With every 10 degrees of temperature change, the deck shrinks or expands about 4.25 inches, he said.

Because the bridge deck is suspended, it also will move in the wind and during earthquakes.

Even traffic will move the bridge slightly, Climie said. A single large vehicle applying its brakes could move the entire bridge an inch or so, he said.

The expansion joints for the new bridge will work like accordions, opening and closing as needed while maintaining an even driving surface.

The joints were manufactured in Minnesota by the D.S. Brown Company.

When the first joint has been off-loaded at the Gig Harbor anchorage, the specially outfitted truck will return to the D.S. Brown plant to pick up the second one.

When the second joint will arrive will depend on the weather, Cornish said, but it is expected to be here in a few weeks.

The deck on the old bridge – completed in 1950 – does not have similar joints. Its deck is made of concrete slabs separated by 44 small expansion joints spaced about 120 feet apart.

Rob Carson: 253-597-8693

rob.carson@thenewstribune.com

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