TACOMA – A problem with the wire being used to form cables on the new Tacoma Narrows bridge has some state officials breathing a sigh of relief that the cost overruns are the contractor’s problem under the “design-build” contract.
The state Department of Transportation said Tuesday that at least some of the 19,000 miles of steel wire being used to form the cables is so badly corroded it is unusable.
Tacoma Narrows Construction is being paid a fixed price to design and build the bridge, so any costs to replace the wire will be paid by the company. The state is concerned, however, about the possibility of delays in construction as the company waits for replacement wire.
“It is bad news,” Department of Transportation spokeswoman Claudia Cornish said. “How bad is yet to be seen.”
Inspectors from Tacoma Narrows Constructors and the state are going through the thousands of four-mile coils of wire stockpiled for use in the cable spinning, looking for signs of the “white rust” discovered on some coils last week.
Cornish said it is too early to estimate how much of the wire is unusable, although about half appears affected to some degree.
The state and Tacoma Narrows Constructors have sent samples of the wire to labs for analysis and are awaiting results. The wire already used in the cable-spinning operation does not appear to be damaged, officials said.
Secretary of Transportation Doug MacDonald said only wire meeting contract specifications can be used on the bridge cables.
“We expect the contractor to obtain additional wire, if necessary, to assure the timely and correct assembly of the suspension cables,” he said.
Getting new cable may be a problem, because the high-strength steel wire was made in Japan and South Korea. Thousands of strands of the wire, which is slightly smaller in diameter than a pencil, is wound into cables on the bridge.
The steel wire is coated with zinc for protection. When the zinc oxidizes as intended, it forms a durable coating that protects the steel. Under some circumstances, however, particularly when freshly galvanized products are stored wet or tightly packed, the zinc can form unstable oxides that eat at the coating.
“You want oxidation on zinc,” Cornish said. “This did not oxidize the way we wanted it to.”
Some of the wire has been stored outside near the new bridge’s Tacoma anchorage. The rest has been stored at covered facilities. Cornish said there might be some correlation between how the wire was wrapped and the amount of corrosion. Two types of wrapping were used, one all plastic and the other plastic with a paper lining. She said the coils wrapped with the plastic and paper seem to be affected the worst.
Spinning crews have been working on the main cables for six weeks. So far, they’ve gone through about a third of the 19,000 miles of wire.
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