The Interstate 5 bridge collapse in Skagit County, WA just showed a HUGE vulnerability for our transportation infrastructure.
The bridge, an overhead steel-truss type, of which there are 340 in Oregon alone, was taken down by an overheight semi-trailer hauling some sort of large steel cube structure, hitting one or two of the overhead truss girders. The energy delivered to the bridge was not very large, as the truck didn't wreck, but continued across the bridge, with the span falling after the truck was clear. There is some evidence that the bridge had been struck earlier by something, maybe a manufactured home, that left shreds of material on the same girders.
Assuming the truck wasn't overweight, and that hasn't been mentioned as a factor, this means that imparting a fraction of the truck's energy of motion at 50 mph or so to the bridge structure was sufficient to dislodge it from it's foundations and put the 165' span into the river.
Every wannabe terrorist now knows a surefire way to do great damage to transportation infrastructure.
The bridges have not been inspected for this vulnerability, either, so no one knows how many of the many thousands of the bridges around the country are at risk, but until proven otherwise, it must be assumed that all are at risk.
A simple idea can protect any bridge from this threat, and that is to install a massive steel arch at each bridge entrance to traffic, an arch just slightly lower than the overhead clearance, but an arch designed, when struck, to stop an overheight vehicle cold. There would have to be serious concrete design work done to anchor such arches, but that's what civil engineers do. This idea, or a better one, must be immediately retrofitted to every overhead-truss bridge deemed of national security interest. BTW, that means railroad bridges also.
This all seems to be of an immediate and necessary claim on available financial resources, but nooooo....
The local fishwrap says that building it's Taj Majal concept (the Columbia River Crossing) of a new Columbia River Interstate 5 bridge, a massive $3.7 Billion pork project, must have the highest priority. This calls for a slap upside the Editor's head with the proverbial Clue Bat, and I just delivered the same:
It's a twisted universe from which springs the idea that the I-5 bridge collapse in WA means we must hurry up and build the CRC.
The biggest lesson of the Skagit River Bridge collapse is that we must use all available money to strengthen our other at-risk bridges, not waste it building the Taj Mahal of all river crossings. If a glancing collision by one or two semi-trailers can put a bridge in the river, we must assure that all our other steel-truss bridges can't suffer the same fate, before we spend a dime on any new bridges. There are hundreds of these at-risk bridges in Oregon, and all must be immediately secured.
There is a national security aspect to this as well, since it has just been demonstrated that a quick, non-explosive way to destroy bridges has just been proven feasible.
It's like casting pearls before swine, however, isn't it?