Previous posts on the new Narrows Bridge:
- History of the Tacoma Narrows Bridges
- The Two Towers I: Intro
- The Two Towers II: Concrete Thinking
- The Two Towers III: Anchor Management Classes
- The Two Towers IV: Out & Down
- The Two Towers V: The Struts
- The Two Towers VI: To the Top
- The Two Towers VII: Stairway to Heaven
- The Two Towers VIII: Spinning Beginning
- The Two Towers IX: Wheels Over Water
- The New Bridge at Christmas
- The Two Towers X: Compacting the Cable
- The Two Towers XI: Cable Banding
- The Two Towers XII: The Cranes
- The Two Towers XIII: Life on the Bridge
- The Two Towers XIV: Heavy Lifting
- The Two Towers XV: The Flying Trapeze
- The Two Towers XVI: Squeeze Play
I have been blogging the construction of the new Tacoma Narrows Bridge. See the above posts for more information on the Narrows Bridges, the engineering challenges, and a first-hand tour taken of the construction site.
With the deck completed, there are still quite a few tasks to complete before the bridge is completed. The cables, comprised of over 19,000 miles of half-centimeter steel wire, joined end to end and woven back and forth as a single unit, have been spun and compacted, but remain unfinished.
To increase their resistance to corrosion, they are wrapped around their circumference with another layer of galvanized steel wire, leaving a smooth surface ready to be painted. The uncovered cables are first covered to minimize the risk of trapping moisture under the wire wrap,
and an impressive rotating spinner tightly winds the steel around the cable like a monstrous black widow spider preparing her prey for dinner.
The cable is first coated with a corrosion-inhibiting paste. For decades, cables were coated with red lead paste, which worked well, but has not been used since the mid-1990s, when the lead was recognized as an environmental hazard.
Bridge builders now use a urethane-zinc paste, about the consistency of mayonnaise. The idea is to apply it thickly, so that it oozes between the wrapping wires to form a solid anti-corrosion coating. The paste is manufactured in Italy, and 1,710 five-gallon buckets were required, each of which weighed 66 pounds.
The cable is wrapped in “bays” — 40-foot sections of cable between suspension bands, 270 in all. Each bay requires 3.3 miles of wrapping wire, a total of 948 miles. Three coats of rubberized paint then complete the finish, giving the cable a solid appearance.
The deck has been completed, welded together and secured with bolted plates, adjusted to exacting tolerances with the precision of a piano tuner. Or a guitar:
The similarity between tuning a guitar and welding is not something just anybody would pick up on.
But to Bill Madron the connection is obvious.
Madron, who \'s an accomplished country and blues musician in addition to being a welding supervisor on the new Tacoma Narrows bridge, says laying down a righteous weld is like making music.
â€œIf you \'re tuning the E string against the A string, you know it \'s right when you hear it,: he said recently. â€œA guitar is either in tune or it ain \'t.
â€œWelding is the same way. It \'s either on the money or it ain \'t.â€
Madron, now 66, grew up in the Appalachian Mountains of North Carolina, â€œa beautiful place to live,â€ he said, â€œbut you can \'t make no money.â€
When he left North Carolina, he took his slow, melodious Southern drawl with him. It helps establish an air of calm on the new bridge deck, where he oversees welding crews joining the 46 deck sections into a continuous mile-long sheet of steel.
Madron started welding when he was 20 and has been at it ever since. As a young man in the 1960s, he combined his work with his passion for music, traveling from town to town, welding by day and playing in clubs at night.
Welding now gets more of his energy than music, but he still finds time to play, wherever his work takes him.
â€œYou know how it is,â€ he said. â€œMusicians find each other. You start playing with somebody, then somebody else comes along.â€
Like music, Madron said, welding is work that takes constant attention and a commitment to quality, and pays off in satisfaction. And, like serious musicians, he said, good welders need to practice constantly to keep their chops.
â€œWelding is part science, part art,â€ he said. â€œIt \'s not entirely one or the other.â€
Normally, it takes young welders at least three years to bring their welding skills to a point high enough to qualify for an exacting industrial job like the bridge, but Madron said career development depends heavily on natural aptitude.
Some people are naturally cut out for welding and take to it immediately, he said. Others never get it.
â€œYou either are a welder or you aren \'t,â€ he said…
The deck itself, whose sections are now joined as a single unit, is still unattached to the anchors. Two giant expansion joints must be placed at either end, to accommodate length changes from changes in temperature, as well as horizontal motion from both traffic, load, and potential earthquake.
These huge joints, manufactured in Minnesota, provided a bit of local drama. The first joint was shipped across 5 states on a monstrous flatbed trailer, happily sailing along until it reached the Washington border — where it ground to a halt, courtesy of the State Patrol.
States have laws governing the maximum vehicle weight allowed on their roads, but vary in how this is determined. Washington determines weight allowances on a per-axle basis: if your load is too heavy, you may transport it legally by increasing the number of axles on the trailer bearing the weight. For huge loads such as this, reconfiguring the axles is no small feat; the original shipping company had to turn the project over to another company, who ultimately delivered the joints safely:
The money quote of this fiasco came from the original trucker: “What I’ve told them is, ‘We’ll do this anyway we can.’ If it’s impossible, then it’s real easy: Y’all can build the bridge in Idaho.”
I love a can-do attitude!