It's starting to look like a bridge. Construction crews at the Tacoma Narrows this week began spinning a thread of wire, back-and-forth...
TACOMA — It’s starting to look like a bridge.
Construction crews at the Tacoma Narrows this week began spinning a thread of wire, back-and-forth, through the concrete towers and the shoreside foundations.
Travelers can now perceive the curve of the future suspension cables, because of safety catwalks that follow the path of the wires being strung. Eventually the team will lay 19,000 miles of wire. A safety notice at one of the Tacoma-side foundations explains some hazards: “Pinch Points. Stored Energy. Watch Hand Placement.”
The thin wires are unreeled from Tacoma to Gig Harbor and back. They are carried on what looks like a large wagon wheel, which rides on another set of cables. Eventually, the wheel will fly by at 11 mph, once everybody gets the hang of things. But yesterday the pace was closer to 1 mph.
Down inside a concrete foundation, Dave Hoffman and Richard Smith each loop a pair of wires around a couple of round anchors, before the wires can head back across the bridge.
“Watch your fingers!” co-worker Monte Gluck calls out, every minute or two. The wires have been slackened temporarily, so the pair can handle them. A timing mistake would easily put each wire under 330 pounds of pressure, near hands and heads.
While Gluck coaches the workers down under, he is taking advice from a Danish bridge expert. He’s also talking to the group onshore that feeds the wire through an elaborate grid of pulleys and spools. That group tightens or loosens the tension.
Every one of 8,816 wires is assigned a precise location. If the wires cross, they might shear each other when tons of roadway hang from them in 2007. If they’re not straight, tiny gaps might be created for water to seep in and cause corrosion. To prevent mix-ups, each wire receives periodic squirts of red, green, black or yellow paint as it leaves shore.
Hoffman and Smith pound the wires with rubber mallets, to make them shimmy into a tighter fit. The wires sound like maracas as they shake against each other.
Karsten Baltzer, a Danish bridge expert, notices a few wires askew. A half-dozen ironworkers huddle where the wires ride several feet away. They slip a rope between the wires and yank it, shaking the miscreants loose. Hoffman and Smith pick up steel lances, to poke and pry around the hangers.
The first few wires set a tone for the next thousand laps. The physics of the classic suspension bridge demand a perfect line.
Workers perched on the catwalks and towers check that each wire slips into its niche, as bridge workers did in Brooklyn, in the Straits of Mackinac in Michigan, in San Francisco, and two generations ago in Tacoma.
Mike Lindblom: 206-515-5631