LOS ANGELES A permanent replacement for a collapsed Pacific Northwest bridge that was initially expected to be built with steel will instead be built with concrete, due in large part to deadline challenges.
The Skagit River bridge on Interstate 5 that connects Seattle with Vancouver, British Columbia, is going to be concrete primarily because "its our fastest option," a spokesman for the Washington State Department of Transportation told AMM.
He said the permanent bridge section must be installed by Oct. 1 and the highway cant be closed until after Labor Day.
A section of the 58-year-old bridge collapsed on May 23 when an overhead steel frame was struck by a truck with an oversized load (amm.com, May 29). A temporary replacement was installed in mid-June.
Initial reports indicated that the state favored a permanent replacement section with six 160-foot-long steel girders that would span from the shore to the initial pier. This led to early estimates that the bridge would need 500 to 1,000 tons of steel, primarily of ASTM A709 grade 50 or similar plate. These estimates were later revised to 200 to 250 tons.
The logistics of supplying the material on the tight deadline worked against steel, according to industry sources, noting that neither of two basic alternatives would have worked. If the steel were sent from the mill, rail transit time measured in weeks would probably have mandated a shipment by truck, which would have driven up the cost prohibitively, sources said. However, if it were decided to use plate out of local service centers, this material would probably have required splicing, again raising the cost.