I-5 Skagit River Bridge Collapses

[haha]

This bridge is just north of Mount Vernon, about 65 miles north of Seattle, and 45 miles S of the border at Blaine, WA/White Rock, BC. No word on any deaths or injuries. This water is very cold, and often pretty swift. The Skagit River originates from glacial feed in the North Cascades. Collapse happened at 7:00 pt.
-One clever guy sitting atop his car.

Ha

[Helen]

Look at that guy sitting on the top of his car. I really hope there were no injuries or deaths.

[DAYDREAMER]

possible oversize load semi hit the bridge girders

[Chuckanut]

When I first heard this news, they said "THE I-5 bridge collapsed!"

'THE I-5 bridge' - like there is only one. I thought it must be the big one that spans the Columbia river going into Oregon. What a mess that would have been. Fortunately, it was a minor bridge over a smaller river. It will still be a mess for quite some time. I-5 is the main highway going from Mexico to Canada. Truckers can't be happy with this problem.

[Meadbh]

Apparently the precipitating event was an oversize load of drilling equipment that hit a support girder. The driver was Canadian. We apologize!

I-5 bridge collapse caused by Edmonton trucker | World | News | National Post

[mn54]

Living in mpls. it immediately brought back terrible memories of the bridge collapse here. My thoughts and prayers for all those affected by this tragedy.

[Meadbh]

Was the bridge stable to begin with?

http://www.thecanadianpress.com/engl...4&languageid=1

Sounds like a single point failure with no redundancy:

http://www.usatoday.com/story/news/n...truck/2357389/

Hopefully some engineering lessons will come out of this.

[haha]

The economic losses will be huge. Cross border retail will suffer little, Whatcom County will gain at the expense of Skagit County (pronounced skajit).

But truck transport between the US and Canada will really be hurt. I-5 is the only interstate served border crossing for many miles to the east. I am not even sure what the next Interstate served crossing might be. Proably somewhere in Montana.

Going east from I-5, there is a mostly 2 lane SR9, and farther east a us highway, also 2 lane.

Vancouver is an even bigger port than Seattle/Tacoma, and very much cross border traffic. And, IRRC, roads trying to go east out of the Vancouver Basin are pretty low capacity.

Ha

[braumeister]

Quote:

Originally Posted by Meadbh The driver was Canadian.

I've heard about those Canadian drivers.

[HFWR]

Quote:

Originally Posted by braumeister I've heard about those Canadian drivers.

Or perhaps it was "weather related"...

[Ronstar]

Quote:

Originally Posted by Meadbh Was the bridge stable to begin with? http://www.thecanadianpress.com/engl...4&languageid=1 Sounds like a single point failure with no redundancy: State of emergency declared around collapsed bridge Hopefully some engineering lessons will come out of this.

Huh? The problem is lack of funding to replace a 58 year old bridge, not the bridge design. Here's a quote from your second link: "The Skagit River bridge, built in 1955, is classified as a "fracture critical" bridge by the Federal Highway Administration. That means it lacks redundant supports elements, not that the design is faulty."

[Htown Harry]

Quote:

Originally Posted by Meadbh Was the bridge stable to begin with? http://www.thecanadianpress.com/engl...4&languageid=1 Sounds like a single point failure with no redundancy: State of emergency declared around collapsed bridge Hopefully some engineering lessons will come out of this.

The strength of the bridge to handle vertical loads from vehicles and the structure's weight is primarily in those horizontal, vertical and diagonal members in the vertical plane along the outside of the bridge (forming a truss). The members in the horizontal plane forming a "roof" provide stability to keep the trusses in place and to provide resistance to horizontal wind loads.

This picture is may be telling. Areas with red primer showing are points where the steel twisted or bent, causing the outer paint coat to flake off. Note the damage to the arched steel member above the man shielding his eyes. It looks like the too-tall load may have taken a chunk out of it. Follow that member to the right, where the vertical piece above the car is kinked toward the inside of the bridge.



One theory that the investigators will explore: the impact to the arching member(s) was so severe that it damaged the vertical members they are attached to. The displacement of those vertical members redistributed the vertical loads carried by the various members forming the truss. One or more of the truss members then became overloaded or unstable as a result, initiating a critical failure in a load-bearing member and starting the collapse sequence.

Quote:

Originally Posted by Ronstar Huh? The problem is lack of funding to replace a 58 year old bridge, not the bridge design. Here's a quote from your second link: "The Skagit River bridge, built in 1955, is classified as a "fracture critical" bridge by the Federal Highway Administration. That means it lacks redundant supports elements, not that the design is faulty."

Bridge design criteria has changed in the 58 years since the bridge with constructed. My interpretation:

A faulty design is one which cannot handle the expected service loads, defined for a bridge superstructure primarily by vehicle weights, the structure weight and wind / ice loads. "Fracture critical" design is related to the redundancy and factor of safety in sizing members and connections for handling overloads and member damage outside normal service conditions.

Today's bridge designs are more forgiving of things like crappy paint jobs, bad welds and dumb truck drivers.

[scrabbler1]

These bridge collapses always give me a chill because they bring back memories of two big bridge collapses in the 1980s in the northeast. One was the Mianus River bridge collapse on I-95 near Greenwich, CT, in June of 1983 and the other was the Schoharie Creek bridge collapse on the New York State Thruway in April of 1987. In the latter, I was driving on the Thruway in the area that weekend in heavy rains (which contributed to the collapse) but did not actually cross that particular bridge. Still gave me the chills seeing pictures of the washed out bridge in the newspaper.

The Mianus collapse caused huge traffic headaches along that heavily traveled highway especially through the upper-class Greenwich community that summer.

[Chuckanut]

Washington state has a history of interesting bridge collapses:

https://www.youtube.com/watch?v=xox9BVSu7Ok