At least some of the 19,000 miles of steel wire being used to build the main suspension cables on the new Tacoma Narrows bridge is so badly corroded it is unusable, the state Department of Transportation said Tuesday.
The bad wire will have to be replaced, raising concerns about possible delays in the project.
“It is bad news,” said the DOT’s project spokeswoman, Claudia Cornish. “How bad is yet to be seen.”
The bridge is scheduled to open in April 2007. In its contract with Tacoma Narrows Constructors, the state has no specific deadlines with regard to completion of the cables. The contract specifies only that the first deck section must be lifted into place on the finished cables by May 7, 2006.
Inspectors from TNC and the state are going through the thousands of 4-mile coils of wire stockpiled for use in the cable spinning, checking for signs of the “white rust” found on some coils last week.
Inspectors are separating the wire into four categories, ranging from “unaffected” to “inappropriate for spinning.” Cornish said it is too early to estimate how much of the wire is unusable, though about half of the wire appears affected to some degree.
“I can’t give you a percentage right now because that’s what we’re in the process of trying to determine,” she said.
The state and TNC 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, the DOT says.
“We feel very confident that the wire spun so far has not been affected,” Cornish said.
Secretary of Transportation Doug MacDonald gave his assurance that only wire meeting contract specifications will 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.
That might be difficult.
The high-strength steel wire is a specialized product made to precise specifications set by bridge designers. Steel used in the wire was manufactured in Japan, then sent to a factory in South Korea where it was made into wire.
The bridge’s main cables are being assembled on the bridge out of thousands of strands of wire slightly smaller around than a pencil.
The wire is high-strength steel, 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 storage facilities TNC leased in the Tideflats area.
Cornish said there might be some correlation between how the wire was wrapped and the amount of corrosion present.
Two types of wrapping were used, one all plastic and the other plastic with a paper lining. Coils wrapped with the plastic and paper seem to be affected the worst, Cornish said.
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.
The wire problem again has given DOT officials cause for relief that the bridge is being built on a “design-build” contract. Under the terms of the contract, TNC is being paid a fixed price to design and build the bridge. Therefore, cost overruns are TNC’s problem, not the state’s.
In September, TNC’s Japanese and South Korean subcontractors – Nippon Steel, Kawada Bridge and Samsung – went to court in a dispute over the reasonable cost of construction of the steel bridge deck, being fabricated in Korea.
Samsung pulled its workers off the job but went back to work after an undisclosed out-of-court settlement by TNC.
Rob Carson: 253-597-8693