Builders battle the wind

TACOMA – Workers on the new Tacoma Narrows Bridge call it “crossing the tree line” the point where they step away from the protection of the shore and into the rush of air that blasts through the Narrows. On windy days, walking onto the new bridge deck can be like sticking your head out a car window on the freeway.

The wind is so strong it sets clusters of heavy steel lifting cables clattering into one another like castanets. Sleet and rain streak down sideways, stinging exposed skin.

Out past the tree line, workers have to wear chin straps on their hard hats to keep them from blowing away.

Tacoma Narrows Constructors is in its 52nd month of bridge construction, racing toward the end of its 58-month construction marathon.

Unfortunately, the bridge builder’s final push is coinciding with the worst weather the Northwest has to offer, making a demanding job more difficult and time-consuming.

November was the wettest month ever recorded in the South Sound, with 15.23 inches of rain falling at the nearby Tacoma Narrows Airport.

The Dec. 14-15 windstorm was the worst in more than a decade. It knocked out power to more than 1 million homes and businesses, including the bridge construction site for most of a workday.

The wind flung a moving van onto its side on the old bridge, prompting the state to shut down the entire span. It was the first time the bridge has ever been closed for wind in its 57-year history.

The wind ripped apart welders’ tents on the new bridge deck, tore away wooden safety railings and broke the lines on a barge, briefly setting one of the 450-ton deck sections adrift in Commencement Bay.

This month, four workers got stuck overnight on a deck section because of high winds. Half a foot of snow recently forced workers off the bridge.

This is not the way things were supposed to happen.

TNC originally planned to lift and join all 46 sections in the 5,800-foot-long steel deck last summer. That way, crews could have waterproofed and paved it in the fall, before the winter weather hit.

But an outbreak of corrosion in TNC’s stockpiled cable-spinning wire in 2005 set them back three months. Then, setting up lifting gantries and winch systems for delivery ships took two months longer than expected.

That meant they’ve had to wrestle the deck sections into the air in the worst imaginable conditions.

The bridge builder shuts down construction elevators when the wind speed reaches 40 mph and pulls workers off the job before that if conditions are unsafe. Darkness complicates things further. This time of the year, Washington gets only about 10 hours of light each day.

TNC has only six deck sections left to hang and expects to have them up this month.

Once the bridge sections are hanging in the right position on the suspension cables, their underlying trusses must be bolted together.

Every one of the 45 section joints requires more than 2,500 bolts, all of which need to be inserted, capped with a washer and a nut, and tightened to precisely the right tension.

Just providing access to all the places that need bolting is a major engineering feat.

For safety, no more than 10 people can be on a platform at the same time, and no one is allowed on them when the wind exceeds 50 mph.

Dangling 180 feet over the Narrows, workers essentially have no protection from the wind and cold. Bundled up in wool, polypropylene and rain gear, they have been managing to complete one joint about every five days, according to Tim Moore, the state Department of Transportation’s lead engineer on the project.

“For them, the cold is the main thing that determines how effective they can be,” Moore said. “When they’re cold, they’re basically just hunched down and looking out for themselves.

“When the wind’s blowing and you’re dripping wet, you don’t stuff a lot of bolts.”

When two deck sections are securely bolted together, the welding teams move in.

Workers at the Samsung Heavy Industries shipyard in South Korea built the sections so precisely that the five-eighths-inch-thick sheets of steel on their tops butt against each other with only a 4-millimeter gap between, too small a space to insert even a pencil.

But the steel on either side of the gaps needs to be welded together so the entire length of the bridge becomes a single mile-long sheet.

Even in clear, warm weather, the job would be technically difficult. The wind and rain complicate it enormously.

The techniques the welders use depend on keeping a layer of gas around the puddle of molten metal to protect it from atmospheric gases and to keep the electric arc stable.

If wind blows the shielding gas away, or if moisture works its way into the mix, the weld is compromised. When it hardens, it could be dotted with tiny craters, an unacceptable, weakened condition welders call “porosity,” or contaminated by trapped hydrogen, which can cause the weld to crack.

To shelter the welders from the winter weather, TNC engineers designed and built special tents that not only keep off the rain, but also withstand the heavy gusts of wind typical in the Narrows this time of year.

The design effort alone took months, said Bill Madron, a TNC welding supervisor.

“There was nothing to go by,” he said. “This is the first big suspension bridge built in the United States in 40 years. We’ve had to come from scratch on everything we’re doing.”

The tents are 80 feet long and about 10 feet high, frameworks of heavy steel pipes covered with 18-ounce black vinyl, the kind truckers use to cover loads on cross-country runs.

Because the steel on the deck is so cold and wet, the welders heat it to between 100 and 450 degrees Fahrenheit before they begin welding.

They also use torches to dry up puddles and divert rivers of rainwater threatening to flow into the tents.

Madron doesn’t even want to guess when the welding might be finished.

“That’s not one I want to touch,” he said. “We’re still figuring out some of the difficulties having to do with the wind.”

Even with the weather-related delays, TNC so far has stuck to its goal of having the bridge open to traffic by July 2, a date three months past its original April 2 deadline and one that lately has begun sounding overly optimistic.

For every day of delay after July 2, TNC will have to pay the state $125,000 in late penalties, up to a maximum of $45 million.