High-Wire Act | The Seattle Times (original) (raw)

Fifty stories above Puget Sound in the black midnight sky, a precious piece of steel dangles from a crane like the weight at the end of an angler's lure.

As the 36,000-pound part is reeled upward, four ironworkers coax it into place at the crown of a massive concrete tower. The men use both hands to spin large nuts clockwise, cinching the piece down. Floodlights form a halo around the summit of the new Tacoma Narrows Bridge, the longest suspension span built in this nation in four decades.

This steel part is called a "saddle" because thousands of miles of cable will ride on it and three others like it over the tower peak, as in the classic bridges of New York. Because an entire saddle would topple the crane, each one was molded in halves at Atlas Castings & Technology, just down the highway.

LATER THIS month, wire will be strung back and forth across these high-rise saddles — a once-in-a-lifetime spectacle called spinning. The sight of workers and wheels on catwalks should cause rear-enders on the old bridge. When the job is done, the pencil-width wires, long enough to wrap twice around the earth, will be bundled into one thick cable on either side, sagging in geometrically perfect, powerful repose between the towers.

So far, the $849 million bridge, to open in 2007, has been a successful feat for a state whose rutted freeways and runaway rail-transit costs have caused malaise.

From the saddles to the underwater foundations, this new bridge depends on both the ingenuity and the lessons learned from the mistakes of two centuries. Its bloodlines run from Scotland through the Brooklyn Bridge to the Golden Gate and earlier spans in Tacoma.

To the 90,000 people a day who drive across this finger of Puget Sound, Tacoma already is a city of destiny. But to generations of engineers, the phrase Tacoma Narrows has been a symbol of failure. The first attempted span, built in 1940, was nicknamed "Galloping Gertie" because it undulated so much that someone driving on it would lose sight of the car in front. Just 129 days after it opened, the deck twisted and collapsed like a strand of wet fettucine. Repeated on newsreels, the breakdown represented "the most ignominious event in engineering history," says Henry Petroski, a bridge expert and professor of civil engineering at Duke University.

That certainly was the image held by Manuel Rondon, a Venezuelan and former oil-rig builder who retrofitted a Portuguese bridge and is now project manager in Tacoma.

He says of the new span: "To a certain extent, it's the redemption of the Tacoma Narrows."

It might also be the last grand suspension bridge erected in America.

TACOMA NEWS reports credit a local rancher, John G. Shindler, with suggesting a span over the waterway in 1888 or 1889, while riding a steamboat. He pointed to the bluffs on either side and said to the boat's commander, "Captain, some day you will see a bridge over these Narrows." The first ferries plied the passage in 1926. A bridge would open up Gig Harbor and the Kitsap Peninsula to growth, and create a road link between the Bremerton naval shipyard and McChord Air Force Base.

An ordinary girder bridge, supported from below like a freeway overpass, would have been unsuitable, because it requires many underwater piers. Those would obstruct shipping and be tough to build in a fjord that reaches depths of more than 200 feet. Tacoma once considered a cantilever bridge, using an elaborate overhead truss that exerts pressure against foundation slabs on the shore. But such a bridge might not support itself over a mile of open water. Such a bridge, under construction, might literally get overextended as one did in Quebec in 1907, collapsing and killing 75 men. Four piers would have been needed at Tacoma.

Floating bridges are ideal for the gentle lake east of Seattle, but not the swirling Narrows.

So the winning concept was the suspension bridge. Its weight is borne mainly by a huge cable hanging like a hammock between a pair of hulking towers.

Each of the 510-foot bridge towers can support the entire weight of Tacoma's population, and each is taller than the Space Needle, if you add the submerged caissons that support them, through about 200 feet of water and soil.

THE WORD caisson is French for "large box." The first ones in the U.S. were used by self-taught designer James Eads for his 1874 St. Louis Bridge. Builders worked inside pressurized metal boxes, which settled into the muck as the soils were pumped away. Twelve men died from "caisson disease," now called the bends, caused by changes in pressure.

By 1939, Tacoma bridge-builders tried a new method, borrowed from a San Francisco Bay project, that kept workers outside the caissons. The same basic strategy was used in 2004, when workers sank the new Narrows caissons.

A shallow cross-section of each caisson is formed on land, then towed by tugboats from Commencement Bay to the Narrows. From above, it looks like a concrete honeycomb of hollow chambers. At the bottom of each chamber is an air-filled barrel, to help float the caisson during the tug ride and for a controlled sinking at the bridge site. At the Narrows, workers on the surface pour concrete in stages into the honeycomb form, each pour plunging the caisson deeper toward the floor of the Sound. After the caisson touches bottom, seawater is released into the honeycomb, where it helps the caisson resist the pressures of the deep. The barrels are sliced up and removed. Finally, mechanical shovels descend through the chambers and scoop up muck from the bottom of the Sound. As the muck is pulled out scoop by scoop, the caisson settles about 60 feet into its new niche.

In Gertie's day, sea pressures made caisson-setting a daredevil task, according to the book "Bridging the Narrows" by crane operator Joe Gotchy, who worked on both Gertie and its 1950 replacement. Divers wore steel helmets and suits that weighed 384 pounds. If the gear failed, "the terrific pressure of the water would most surely crush his body to a pulp," Gotchy noted. One diver, Chris Hansen, lost his air line while working on an anchor that kept the caisson from drifting. He popped to the surface 40 yards away, spread-eagled. "He had closed the exhaust valve on his helmet so that he had flotation. Coming up that fast with air at better than 60 pounds pressure, he was lucky his suit did not burst. He had to go into the decompression tank on the diving scow," Gotchy wrote.

Even today, much can go awry.

Last year, the divers who helped plant the anchors had to avoid tangling in Gertie's sunken beams, some of which were removed for safety. Tug crews had to sidestep the existing bridge towers. Sometimes, crews in skiffs would drift out of position, says Terry Maxwell, a pile-driver foreman. "Everything's under an extreme load when you're setting the anchor and pulling. You make sure you're in the right spot, so if something breaks, you won't get cut in half." During the job, one anchor chain ruptured underwater, forcing engineers to recalculate stresses and positions.

Still, the center of each caisson touched ground within a bull's-eye as small as a quarter, according to state Transportation Secretary Doug MacDonald, who called it the riskiest phase of the project.

"The project staff really breathed a big sigh of relief when the caissons sunk," he says.

BECAUSE THE cables of suspension bridges all obey the same laws of physics, the only way to create a distinctive shape is through tower design. In the Brooklyn Bridge, giant brick towers dominated the skyline and later formed a poignant old-world frame for the twin World Trade Center skyscrapers, says bridge expert Petroski.

In Tacoma, bridge-design firm Parsons, the state and a construction partnership of Bechtel and Kiewit chose concrete instead of steel that would have matched the 1950 towers.

Historic preservationists thought a steel replica would detract from the existing bridge, state officials say. The lower price of concrete sealed the decision.

The two new towers, each formed of two hollow concrete legs, are nearly the same height as the old ones, and have decorative X-shaped imprints to mimic X-shaped braces on the steel bridge.

"I think they wanted to split the difference, one that echoed thematic patterns of the bridge that was there, but enough difference to not appear like a twin," says Narrows historian Rick Hobbs.

As the legs of the towers rose, motorists noticed they slanted toward each other.

"We get asked all the time, 'Do you know that they're leaning?' We do," says field engineer Scott Ireland.

The space between the lower legs is wider than it is at the peak, forming an A shape. That is so the entire deck can hang between the towers without hitting them. On the existing bridge, there's no room for safety shoulders, and sidewalks bend awkwardly around the tower legs.

The tower concrete was poured inside plywood chambers that Tacoma workers nicknamed "birdcages." After each 17 ½-foot layer hardens, the cage is jacked up to the next level and bolted temporarily to the tower face. Inside, vertigo is forgotten and there is virtually no risk of falling. The only thrill is traversing an open-air walkway between the two tower legs. (Gotchy witnessed two men drown while building the 1950 bridge, but now, workers are under constant harness or enclosure.)

At a morning tower pour on the Gig Harbor side of the bridge, a boom box blasts Red Hot Chili Peppers and ZZ Top as workers hop in and out of floor hatches. Some carry a plastic tube across the walkway to aim fresh concrete into the plywood crannies. To control the spout, Kim Davies yanks on a bar that resembles the bar on a ski chairlift. The concrete aggregate is the consistency of oatmeal filled with frozen blueberries. "Aggregate jams up, and you've got to wiggle it once in a while," explains superintendent Ed Kellison. This particular load isn't spreading fast enough, so Kellison complains by cell phone to the batch plant. "Our mud was a little bit stiff," he says. The gray gelatin must be stirred and shaken right away, to pop any air pockets before the concrete hardens. Across the gangway, ironworkers on the other leg attach more steel reinforcing bar, so the next layer of the leg can be poured soon. The rebar clangs like horseshoes as the workers fight a 1:30 p.m. deadline, when an inspector will show up. There's also a competition to complete their tower before the Tacoma tower, for bragging rights.

"We've got to go out and beat those guys across the way. We're kind of racing a bit," says Dan Weed, a tall, 35-year-old union ironworker from Bonney Lake. "On our radio, we call over there, kind of razz them. We'll tell them, 'Look to the west, Bro!' " The Gig Harbor crew reached the pinnacle June 7, five weeks behind schedule — but ahead of the Tacoma gang.

"In a figurative sense," says secretary MacDonald, "the towers have leapt up."

FOR TWO CENTURIES, engineers have worked to craft suspension bridges that are rigid enough to hold their shape yet flexible enough to absorb forces.

As early as 1837, wind destroyed a suspension bridge in Scotland, and some New York bridges swayed excessively. But by the time the first Tacoma bridge was designed, engineers had forgotten history, and in their hubris were attempting longer and thinner spans, Petroski shows in his book, "Engineers of Dreams: Great Bridge Builders and the Spanning of America."

"Even before the Tacoma disaster, rumors were current regarding oscillations on several recently completed suspension bridges of a wide variety of proportions," said a report by UW professor F.B. Farquharson, who tried to solve its problems just before the collapse. With just two traffic lanes, Gertie was uniquely scrawny with a 72:1 ratio between length and width. That size, plus its flat, wind-catching girders below, doomed the bridge.

Farquharson was the last man on the deck, scrambling to shore as the bridge twisted at a 35-degree angle. The existing 1950 bridge is wider and stiffer, and now considered overbuilt.

The new bridge flexes in astounding ways.

Just before the main suspension cable is spun across the new span, the concrete towers will be pulled toward shore, temporarily bending each one up to 23 inches. That force will offset the weight of the huge cable and the steel bridge deck so that those parts pull the towers back into position. Even on a normal day, when the sun shines, the towers will move 4 to 6 inches as heat affects the cables.

To prevent another Gertie-style gyration, the deck is designed to sway sideways 15 feet in a 150-mile-an-hour windstorm.

When the Golden Gate Bridge celebrated its 50th anniversary in 1987, the weight of 300,000 people made the bridge sag grotesquely at midspan. To avoid that, Washington state transportation officials expect they'll close a few lanes to pedestrians during their new span's opening-day ceremonies in 2007.

THE WORD "pontiff," used to describe the Pope, is derived from a Latin word for bridge. A "pontifex" was a Roman priest who served as the spiritual bridge between man and the gods. In the New World, the chief engineer of a successful suspension bridge — usually a charismatic personality — could earn from his peers the appellation Pontifex Maximus, Petroski's book says.

Not in Tacoma, where only the bridge takes a high profile.

"Today we operate on the anthill theory of public-projects management," MacDonald says. "Every ant carries one grain of sand."

Still, suspension bridges can reflect a glint of the divine.

The Tacoma Narrows profile follows the "Golden Section," a rule of proportions favored by Leonardo DaVinci and correlated with beauty in the human face, or the shape of a tree. The ratio of its mainspan to a side span is the same as between the whole and the mainspan — a number known as phi, approximately 1.6.

Today's technologies could have allowed cheaper construction by setting the caissons on land, but designers put them in the water, for the sake of the Golden Section and symmetry with the old bridge, says Dave Climie, a Scotsman who is the project's superstructure manager.

The new towers, tapering but never joining at the top, look more like broken wishbones than classic spires. MacDonald admits the concrete diminishes their beauty.

"They don't soar the way the old Tacoma Narrows Bridge does. They're not as evocative as the Golden Gate Bridge. They lack the power of riveted steel. People are going to be struck that this bridge is not as graceful, but the elements are heavier and more and more ponderous."

Nonetheless, he says that by comparison, the nation's other new suspension bridge — the thinner Al Zampa Bridge across Carquinez Strait northeast of San Francisco — "is not nearly as fun."

The Carquinez span, he adds, is "totally devoid of architectural character, I think. The towers are too plain and inelegantly proportioned even to be called appealingly austere in their functionality." The Narrows also boasts a superior setting, he opines, amid Puget Sound whitecaps and Olympic mountain snowcaps.

Bart Ney, spokesman for the Carquinez bridge, passed up his chance to woof at Tacoma.

His span doesn't need heavy cross-members, he said, because its thin tower tops stand firmly on their solid piers, like a baseball player's stance in the batter's box.

"Much like the no-nonsense ironworker the Zampa bridge was named after, this bridge doesn't carry anything extra to get the job done, but does the job with a flair all its own."

MOST OF THE excitement in suspension bridges has shifted to Asia, where the world's longest one opened in Kobe, Japan, in 1998, and where the Chinese have built two gargantuan spans across the lower Yangtze River. The new Narrows span is the longest of its kind in North America since the Verrazano-Narrows Bridge opened in New York in 1964.

Professor Petroski is unaware of any new suspension spans planned in the United States. Most suitable waterways in this country have already been bridged, he says, so about the only prospect for more suspension bridges would be to match or replace existing ones.

He also speculates that the style has been eclipsed by the cable-stayed bridge, where taut wires reach directly from the towers to the road deck. The first of these in the U.S. was the Ed Hendler Bridge over the Columbia River between Pasco and Kennewick, in 1978. Another is Tacoma's Highway 509 bridge over the Thea Foss Waterway.

Unlike a suspension bridge, whose physics determine a signature shape, a cable-stayed bridge lets designers play with spoke-and-hub patterns.

"It's a more modern form. People feel it's got more signature status," Petroski says.

Cable-stayed design wasn't considered in Tacoma because towers would have needed to be about 900 feet tall, which would overshadow the old bridge and disrupt an airfield.

As for the future, even if Gig Harbor becomes a metropolis, there won't necessarily be a third bridge. Instead, a lower deck can be hung from the second bridge by building a concrete cap and another set of saddles above the saddles. One long-range scenario would be adding light rail in about 25 years, says John Ladenburg, Pierce County executive and current board chairman of Sound Transit.

That's been done in Lisbon, Portugal, where Rondon — now the Tacoma boss — led the installation of a second suspension system and deck without stopping traffic on an existing bridge.

Years sooner, the Narrows crossing will be recognized worldwide, Ladenburg thinks. "Every time you see the twin bridges, it's Pierce County. It won't look like the Golden Gate or any other bridge."

While the bridge may be grand, Jennifer Kilmer of the Gig Harbor Historical Society discounts the notion that locals will become obsessed with tall towers and graceful cables as a sign of self-esteem. Looking into the archives, she noticed two themes the 2007 bridge shares with the sunken 1940 bridge:

"One is a fear of growth on the peninsula because of easy access; and the other was a dislike of the tolls."

Sometimes, a bridge is only a bridge.

Mike Lindblom is a Seattle Times staff reporter. Steve Ringman is a Times staff photographer.

One of two concrete towers for a second Tacoma Narrows Bridge rises alongside the old bridge this summer as workers on the two towers compete to finish first. When completed in 2007, the new suspension bridge might be the last of its breed built in America. (STEVE RINGMAN)

How the bridge was built
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A support cable on the Gig Harbor side of the new Tacoma Narrows suspension bridge literally pulls the new tower toward land before the main support cables are strung into place next month. (STEVE RINGMAN)

Gig Harbor school principal Jay Reifel fly fishes for salmon on the Gig Harbor side of the Tacoma Narrows at dawn. The towers of the new bridge will rise 510 feet above the caissons that support them near water level. (STEVE RINGMAN)

Working about 400 feet above the channel, Kim Davies pulls a load of fresh concrete into position before releasing it inside one of the birdcages used to form the massive towers. (STEVE RINGMAN)

Seen from a spot high on the old bridge, the two legs of a tower for the new span rise. Atop the legs are the birdcages used to form the tower legs. The old bridge towers are steel, but the new ones are concrete because it was cheaper. (STEVE RINGMAN)

Dennis Engel, project engineer for the new $849 million Narrows bridge, walks through an underground chamber where the main suspension cable of the old bridge is divided into smaller cables. Similar structures, called anchorages, are being used at each end of the new span. (STEVE RINGMAN)

The old suspension bridge relies on the strength of steel cables to hold up the deck across a mile of open water. About 19,000 miles of thin wire will be spun into a pair of huge cables, one for each side of the new bridge this fall. (STEVE RINGMAN)

Troy Bertch works his way around the interior of the birdcage, tying up the rebar that will support the next pour of concrete in shaping the towers. The legs of the towers lean toward each other, forming an A shape, wider at the bottom so the entire deck can hang between the legs without hitting them. (STEVE RINGMAN)

On a walkway between the legs of the west tower, Kim Davies of Tacoma takes the back of a pipe behind Quang Long of Port Orchard. The two are heading for one of the birdcages. (STEVE RINGMAN)

The graceful lines of the suspension bridge hint at the technical complexities of the design; such a bridge must be both rigid enough to hold its shape and flexible enough to absorb the shock of wind, waves and other pressures. (STEVE RINGMAN)

The 1950 Tacoma Narrows Bridge, on the north side of the new span, was built to replace the infamously unstable Galloping Gertie, which collapsed just 129 days after it opened. (STEVE RINGMAN)