Plans to build a temporary replacement section to the collapsed I-5 Skagit River bridge in Washington State were nearing fruition this week, as safety investigators described the collapse as a “wake-up call”.
The truss bridge, which lies some 60 miles north of Seattle on Interstate 5, collapsed on 23 May when a truck carrying an oversized load hit a steel girder (NCE 24 May).
Ten truckloads of parts have arrived on site for construction of a temporary four-lane ‘Bailey Bridge’ to span the 54m chasm. Washington state governor Jay Inslee has promise to get the bridge running this month; and a permanent fix by autumn.
Inslee said: “Crews will put temporary piers into the river to support a platform adjacent to the collapsed span where the new section will be built.
“Once complete, the temporary span will be removed and the new permanent span will be moved into place. [We] hope to have the permanent bridge open to traffic in early fall.”
The 58-year-old bridge is among 18,000 classified by the Federal Highways Administration (FHA) as ‘fracture critical’ - meaning those that lack ‘redundant supports’.
Gordon Masterton, chairman of the UK’s Standing Committee on Structural Safety, explained: “Where you have a lack of redundant supporting elements if you take out one critical member there is no alternative path for the load, resulting in collapse.”
Masterton added of the Washington collapse: “It’s not a case of lack of maintenance; it could have happened a day after opening.”
The FHA says the 18,000 fracture- critical bridges account for about 3% of the US’s 600,000 bridges, which are an average of 42 years old.
Debbie Hersman, the chair of the National Transportation Safety Board, which is investigating the Washington collapse, admitted that the failure was a ‘wake up call’.
“This is a really significant event and we need to learn from it, not just in Washington but around the country,” she said.
In a televised press conference she confirmed that the company that owned the truck which caused the collapse had a license for an oversize load and that it had also used a pilot car; the driver of which they were yet to question.