Special Reports

New wire for bridge to replace corrosion

The builder of the new Tacoma Narrows bridge reaches deals with three international suppliers to replace at least 3,800 miles of damaged wire. The search for wire is over.

Tacoma Narrows Constructors has contracted with three wire manufacturers – in China, South Korea and England – to replace at least 3,800 miles of stockpiled cable wire ruined by corrosion.

Spokeswoman Erin Babbo said the builder of the new Tacoma Narrows bridge placed orders with three suppliers “to diversify our sources and secure delivery in the shortest time possible.”

The new wire will be produced and shipped on a rush basis, but even so, the first shipment will not arrive in Tacoma until late March, TNC says.

That puts a crimp in the bridge builder’s schedule.

TNC had planned to have the bridge’s two main cables completed last month, enabling crews to install the big gantry cranes that were to begin lifting sections of the steel deck into place in March.

Now it looks as if the north cable won’t be completed until April at the earliest.

When finished, each of the two mile-long main cables will contain 8,816 individual wires, each about the diameter of a pencil.

TNC officials acknowledged for the first time last week that they might miss a state deadline that calls for having the first of 46 steel deck sections in place by May 7.

TNC emphasized, however, that the date is an interim deadline only and that it intends to have the bridge finished as planned in April 2007, as previously predicted.

The $849 million bridge project is about 76 percent completed.

TNC will incur no financial penalties if it misses the May 7 deadline, but it will have to present a revised work plan that details how it will make up the lost time, said Linea Laird, the state Department of Transportation’s manager of the bridge project.

Also, because the bridge is being built under a “design-build” contract, the amount the state will pay for the bridge won’t increase because of the ruined wire.

TNC is being paid a flat fee of $615 million for designing and building the bridge, plus state change orders, and will have to take responsibility for the extra cost of buying more wire.

TNC does not reveal what it pays its subcontractors.

One of the wire manufacturers producing the replacement wire is Kiswire, the original South Korean supplier.

The quality of the steel wire and its zinc coating when it left the Kiswire plant is not in question, Laird said.

What caused the corrosion remains unknown.

The coating is meant to weather into a nonporous form of zinc carbonate that makes a hard, protective coat for the steel beneath it.

Instead, the zinc on some of the wire reacted differently, forming a porous form of zinc carbonate, a white fluffy substance sometimes referred to as “white rust.”

Unless that chemical process is interrupted, the zinc coating is destroyed, exposing the steel to the weather.

The corrosion problem initially was attributed to improper storage. Some believe the way the coils of wire were packaged was the critical factor.

Crews have been sorting through stockpiled wire near the Tacoma anchorage for the past month and a half.

Chemical labs hired by TNC and the state will continuing their tests on the remaining wire through this week at least, taking samples to assess how much zinc coating remains.

Wire that is only lightly corroded is being cleaned by pressure washing and brushing with stainless steel brushes.

The unusable 4-mile coils are being identified, tagged and separated from the rest.

TNC estimates that “at least 20 percent” of the wire is too corroded to use. State officials have said they are confident that none of wire already on the bridge is damaged.

Laird said she was not particularly concerned about how much bad wire is eventually discovered.

“That’s a TNC issue, and I don’t want to get in the middle of it,” she said. “My main concern is that no bad wire gets used on the bridge, and I’m completely confident there will not be.”

Rob Carson: 253-597-8693

rob.carson@thenewstribune.com

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