Thursday, May 23, 2013

Tonight's I-5 Bridge Collapse Reminds us to Preserve and Maintain First; Third Bridge Can Wait - Updated

This is terrible. Tonight multiple media are reporting that a section of the I-5 Bridge over the Skagit River has collapsed.

Some have suggested that it is the bridge on WSDOT's list of "structurally deficient" bridges.

The bridge seems to have been built in 1953.

As we consider a giant bridge and highway for $800 million, this is a reminder that the Marion Street Bridge is also rated "structurally deficient," and the Center Street Bridge just above the threshold for "deficient."

We need to focus on repairing, preserving, and maintaining before we think about building a new giant bridge and highway.  Really.

Update, Saturday, May 25th

So now we have some facts. From the Seattle Times:

Year built: 1955
Number of spans: 4
Materials: Concrete cast deck; steel trusses
Average daily traffic (2007): 70,526
Trucks: 12% of total traffic
Sufficiency rating: 57.4
Superstructure condition: Fair, 5 of 9
Substructure condition: Satisfactory, 6 of 9
Deck condition: Satisfactory 6 of 9
Source: National Bridge Inventory 2010

It was "functionally obsolete" rather than "structurally deficient."  By contrast, the Marion Street Bridge rates 6/5/4 and 29.7 - the Skagit was 5/6/6 and 57.4.  The Marion St. Bridge is rated "structurally deficient."  The particular design of the Skagit Bridge also meant that it was "fracture critical," and liable to failure at a single point - like a truck strike might create.

1 comment:

Salem Breakfast on Bikes said...

updated with info about bridge