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WSDOT: Bridge mishap not standard procedure
A 30-ton crane that toppled over on the Tacoma Narrows Bridge early Monday morning destroyed a large section of railing but caused no structural damage to the bridge itself, according to the Washington State Department of Transportation.
Spokeswoman Claudia Cornish said the crane fell because its boom (or arm) was turning after its outriggers had been retracted, which is not standard procedure.
Asked if the accident was caused by human error, Cornish said she asked that question of Tacoma Narrows Constructors (TNC).
What they are willing to say is that the action of (turning the boom) was the cause of the tipping, she said. But beyond that, they are not prepared to say.
Cornish said WSDOT engineers examined the bridge after the incident, which closed the bridge at least partially for more than 12 hours, and found no damage to its key structural components, but that the deck suffered some indents in the asphalt.
However, she said a 32-foot section of the pedestrian railing was struck by the falling boom and will have to be replaced. Currently, she said, a temporary cable railing is in place until a permanent one can be installed, which should be completed in about a month.
Cornish said the crane was being used to remove temporary enclosures on the existing bridge that allowed crews to make seismic upgrades, while keeping the bridge open to traffic.
While the crane was not involved specifically in building the new bridge, she said the seismic upgrades to the old bridge are part of the overall new TNB project because in addition to building the second span, it includes upgrades of portions of the existing bridge to meet current seismic codes.
Although WSDOT had planned to continue the strut enclosure removal work for the next several days, along with slowdowns and lane closures, Cornish said that work has been suspended until further notice.
She said while cranes and heavy equipment will be used in the future on the bridge, that particular crane will not be used to remove the remaining enclosures on the (bridge) strut.
Cornish said the removal of the crane was such a time-consuming process requiring a 6.5-hour total closure of the bridge because of the precarious position of the crane boom, which had nearly its entire length hanging off the side of the span.
Many preparatory steps needed to take place before the crane could be removed, she said, which included bringing several pieces of heavy equipment to the site, disassembling and removing the fallen cranes counterweights and boom, righting the crane body itself, then installing temporary railing after removing the damaged section.
She said TNC will be responsible for cost of the repairs, and it will not passed on to tollpayers.