Ballet on the Narrows
Rob Carson; The News Tribune
In the world of suspension bridges, Dave Climie is an international superstar.
Before he turned 40, the Scottish engineer masterminded the cable-and-deck systems on three of the five largest suspension bridges in the world.
When Bechtel Corp. headhunters went looking for him in 1999, hoping to convince him to come to work on the new Tacoma Narrows bridge, he was in China, stringing the world's fourth-longest main span across the Yangtze River.
Climie is the Lance Armstrong of bridge construction engineers. He was in charge of the cable-spinning operation, which included running 19,000 miles of wire back and forth on trolleys across the tops of the new bridge's 510-foot towers.
But the act soon to start at the Narrows will be Climie's pièce de résistance, as well as the grand finale of the five-year construction show.
Over the next five months, he and his team of engineers, technicians and ironworkers will lift the new bridge's mile-long deck - all 40 million pounds of it - more than 200 feet in the air and hang it on wire ropes dangling over the Narrows' fast-moving currents.
"This is when things start getting really interesting," Climie said. "It's a bit like a giant construction set."
The operation did not begin well. The ship carrying the first 16 of 46 deck sections would not fit under the existing bridge when Tacoma Narrows Constructors tried to move it into place Friday. That gave Climie and his fellow engineers a new problem to solve. (They figure more ballast on the ship will do the trick.) The first section is to be lifted within the next three weeks.
The big lift is a production Climie has spent five years preparing for, including 21 trips to South Korea's Koje Island, where the deck sections were manufactured. He crawled around on them with micrometers and millimeter rulers to make sure they fit together.
Back in Gig Harbor, he and his team spent thousands of hours planning and rehearsing every detail of the lifting sequence.
'ABSOLUTELY!'
In spite of his vaunted stature among engineers, Climie is a modest and unassuming man.
His natural charisma is enhanced by his Scottish accent and sometimes unusual word choice. In conversation, he comes up with words like "festooned." Describing the curve of the main cables, he says "ca-TEN-ary" instead of "CAT-enarry." His frequently punctuates his speech with an enthusiastic "Absolutely!"
Explaining how the deck-lifting process will work, Climie is part professor, talking about plate anchors and parabolic curves and dynamic positioning thruster systems. He's also part little boy, waving his arms and talking fast about how cool it's all going to be.
And it will be cool.
Aside from the fact that the operation will be performed in midair, what makes it especially interesting is that it combines such enormous scale with such exacting precision.
Even the smallest deck sections are bigger than houses and weigh more than railroad locomotives. The largest is 155.9 feet long and weighs more than 1 million pounds. Walking at a normal pace, it would take 35 seconds to get from one end to the other. Climbing from the bottom chord of any of the sections to the top would take a ladder with 80 rungs.
Still, when the deck sections are lifted into place and bolted together, the gaps between them will be no wider than a pencil.
A steel plate on top of each section will be welded to the adjoining ones, and Climie and his fellow engineers have gone so far as to work the shrinkage of these welds into their calculation of the total length of the finished deck.
"There are 45 joints and each will shrink 2 millimeters," Climie said.
That's a total of about 3.5 inches. The finished deck will be 5,400 feet long, he said, plus or minus one-eighth of an inch. That's when it's measured at 64 degrees Fahrenheit. The length changes by 4.25 inches for every 10 degrees of temperature change.
EXPERTS AT WORK
Climie is in charge of the lifting operation, but much of the technical expertise and equipment came from Japan. TNC's Japanese subcontractor, a partnership of Nippon Steel and Kawada Bridge, sent a team of six suspension bridge experts to Gig Harbor, where they've been living with their families since March 2005.
"This is all about having experts doing what they know," Climie said.
The NSKB team brought highly specialized construction equipment with them, an assortment of bright blue compactors, trolleys and spinning spools that at times have made the construction site look like a carnival.
The most obvious pieces of equipment on the job at the moment are the big gantry cranes perched on top of the main cables.
The cranes - rolling platforms that crawl along the cables like ultra-slow-moving trains on railroad rails - are the workhorses of the lift operation. Their powerful electric motors and hydraulic jacks run the winches that do the lifting.
The gantries work in pairs, one set on each of the side spans and two sets in the midspan. Inside control booths midway between the main cables, the crane operators will work the cables below them like puppet masters with marionettes.
From that height, nearly 500 feet, Seattle high-rise office buildings 25 miles away are clearly visible. Seals swimming in the water below are so small they look like flagellated protozoa on a microscope slide.
The gantry cranes will pluck 10 of the 46 deck sections directly off the ocean transport vessels anchored beneath the bridge's west- side span, about 300 feet from the Gig Harbor shore.
The rest will be transferred from the ship to a barge specially outfitted to maneuver in the Narrows' notorious currents. The barge then will haul them into position for lifting. The gantry cranes will handle those 36 sections three times each: once to take them off the vessel, again to load them onto the barge and finally to lift them into position at deck level.
In all, the cranes will do 118 lifts of the sections.
The sections will not be installed one after the other in a linear fashion. Instead, they'll be placed in strategically staggered positions along the bridge to balance the stress on the suspension cables.
Too much stress on any portion of the cables could cause them to slide out of position in their saddles on the tower tops.
Even with balanced loading, Climie said, the tower tops will move back and forth as much 2.5 feet as sections are added.
Safety regulations forbid workers from riding up with the loads, so one team of ironworkers on the barge will hook up the sections to the cables dropped from the gantries.
When a section is in position at the deck level, another team of ironworkers will be lowered onto them from the catwalks in hanging mesh cages called "man baskets."
Eight workers will descend to the sections and secure them to the suspender cables by slipping steel pins through holes in brackets on the deck sections and sockets on the suspenders.
The pins they'll use are about the size of a beer bottle and weigh 15 pounds each. Securing each section is expected to take about 30 minutes.
That would be spectacle enough, but Climie has a special flourish planned.
Because some sections will need to be suspended over land or within the legs of the towers, they can't be lifted straight into position. Those sections, 16 of them, need to be swung or "trapezed" into place.
'IT'S GOING TO HAVE A SAG IN IT'
To swing a section, crews will attach it not only with vertical cables but also to cables that extend in front of it. Using a combination of winches, they'll gradually take the weight off the vertical cables and transfer it to the angled cables, swinging the section forward.
The first section off the transport vessel and onto the barge will go straight to the middle of the bridge, most likely by mid-July.
When the main cables take the 925,000-pound weight of the first section, they will drop 12 vertical feet.
"When people see it, they're going to think something is horribly wrong," Climie said. "It's going to have a sag in it."
Do not fear, Climie said. "That's the way it's supposed to work."
Is he sure about that?
"Absolutely!"
Rob Carson: 253-597-8693
rob.carson@thenewstribune.com
