Bridge in Washington State collapses 6

[bridgebuster]

Mike - I should have done it a few years earlier when the exchange rate was about $0.75 rather than the current $0.97. Anyway, I'll make it up in my fee. Funny thing, I just happen to have a set of plans for a bridge that size. ;-)

 

[dik]

from the Winnipeg Free Press:

SEATTLE - The chairman of the National Transportation Safety Board said Saturday the bridge collapse in Washington state is a wake-up call for the nation.

"This is a really significant event and we need to learn from it, not just in Washington but around the country," Debbie Hersman said after taking a boat ride on the Skagit River below the dramatic scene where a truck bumped against the steel framework, collapsing the bridge and sending two vehicles and three people falling into the chilly water.

Investigators need to find out what happened in Washington and if it could be repeated at similar bridges around the country, Hersman said.

 

[chicopee]

Was a bridge inspection conducted after the oversized vehicle hit the bridge? It would not be hard to buckle these bridge members and Washington DOT would have been called by the police for an inspection.

 

[msquared48]

As a correction to my earlier post, the clearance of the Skagit River bride was 15'6" and the truck oversized height was 15'9". So this bridge has more clearance than the Snohomish River Bridge.

And yes, I agree with the NTSB that this design could be a major flaw in the Interstate Highway System, a trigger just waiting to be pulled. Moreover, how much weakening to the structure had been done with earlier hits? The one that I am aware of was on the south side of the bridge, not the north, but I imagine there were many others, some documented, some not. The "straw that broke the camel's back" scenario here could be playing out too.

Mike McCann
MMC Engineering

 

[msquared48]

I just read a similar article to what dik posted, and it says further that:

"State officials approved Mullen Trucking in Alberta to carry a load as high as 15 feet, 9 inches, according to the permit released by the state. However, the southbound vertical clearance on the Skagit River bridge is as little as 14 feet, 5 inches, state records show. That lowest clearance is outside of the bridge's vehicle traveling lanes, Transportation Department communications director Lars Erickson said Friday. The bridge's curved overhead girders are higher in the center of the bridge but sweep lower toward a driver's right side.

The bridge has a maximum clearance of about 17 feet, but there is no signage to indicate how to safely navigate the bridge with a tall load.

At a news conference later Saturday, Hersman said Washington state does not require signage unless the clearance is 14 feet, 4 inches or less.

The permit specifically describes the route the truck would take, though it includes a qualification that the state "Does Not Guarantee Height Clearance.""

So, I am not really sure what the height clearance is or was as I have heard many different values here. In my opinion, but what do I know, what should be posted, or recorded. is the minimum height to the underside of the superstructure in the traveled roadway, whatever that was. The trucker must have moved to the left after he hit the initial portion of the bridge, as none of the other curved members, that all appear to be of the same geometry as the first from a Google Maps roadway view, appear to have been hit. Time will tell...

Mike McCann
MMC Engineering

 

[msquared48]

Here is a link to that article...

http://www.komonews.com/news/local/NTSB-Bridge-collapse-in-Wash-is-wake-up-call-208963011.html

Mike McCann
MMC Engineering

 

[TGS4]

chicopee - the collapse happened almost instantaneously after the collision. The truck driver reported looked in his side mirrors to see the bridge collapse immediately after he left the bridge.

 

[hokie66]

The msn.com article which M^2 referenced earlier talks about previous damage to this bridge. Apparently it was inspected 6 months ago for high load strikes...it didn't say whether repairs were completed.

 

[msquared48]

http://www.komonews.com/news/local/Temp-bridges-planned-for-fallen-I-5-209008501.html

Mike McCann
MMC Engineering

 

[briancpotter]

Looks like the narrative is shifting to "the danger of fracture critical bridges":

http://www.slate.com/blogs/the_slat...idges_across_u_s_are_at_risk_of_collapse.html

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[hokie66]

Murphy knocked it down, Bailey puts it back.

 

[msquared48]

...which is where it should go in my opinion.

Mike McCann
MMC Engineering

 

[msquared48]

I think I am going to sell ferry tickets online.

Mike McCann
MMC Engineering

 

[dik]

A humourous reply from a Winnipeg Free Press reader, "Doesn't anyone see the plants growing on the tops of the concrete pillars???? Right where the steel bridge rests? I think we all know that plants cause moisture and moisture causes RUST! Therefore, the bridge rusted and collapsed and it hit the semi-truck. The semi did not hit the bridge!!"

Dik

 

[dik]

Mike... it's legal in Washington!

Dik

 

[dhengr]

“Fracture critical bridges,” b.s...., those talking and writing heads don’t have the vaguest idea what they are talking about, but using big words and phrases impresses the reader/listener. They are parroting something they have heard with little to no knowledge of the facts of the matter. I must confess, I’ve not seen either of these bridges, and didn’t witness the accidents either. But, I’ve inspected a few bridges after the fact, and been involved in HW&H shipments by truck and rail over the years. I am not trying to downplay the importance of redundancy in structures or the fracture critical nature of some structures. But, we have never designed highway bridges to have primary structural members hit/impacted/ripped out by a 30-40 ton tractor-trailer with a high load and not be seriously, maybe critically damaged. And, we don’t design multi-track railroad underpass bridges to withstand the impact of a fast moving train, or the derailment and collision of two trains, right under the bridge, and not be seriously damaged, maybe moving a pier top a few inches. If we don’t have enough money now to manage, maintain and renew our bridge infrastructure, just wait until we start designing and building for these slim possibilities; we won’t have enough material or money for one bridge.

The likelihood of the collision/derailment right under a highway bridge, as happened in MO, is really pretty slim when you consider ton/miles or track miles of railroad transport activity. This isn’t something we can practically or economically design against, we can’t afford to do that. We haul HW&H (high, wide and heavy) loads over the highways every day. It takes some clearance, structure load cap’y, and actual movement planning and study to do it right. Not just a car with blinking lights in front of the truck. Railroads and highway depts. have people who do this on a regular basis. If the state gave the trucking company a permit for 15.75', they would normally give some advice about critical clearance locations below that elev., but with no guarantees. That trucker should have had a route/trip plan which said stay in the middle lane at the Skagit River bridge, 17' clr. for a 15.75' load, is no biggy, and he should not have been going 40-60mph crossing the bridge either. That wasn’t even a particularly high or heavy load, was it? Someplace, I thought I saw a video, maybe only a recreation, showing the truck hitting the bridge, and continuing on, and the bridge falling seconds later. It seems that we would be wise to let these things develop a bit, before we pass final judgement. As knowledgeable engineers, we might do what we can to prevent (or correct) the talking heads from pushing the negative and spectacular for the sake of air time. And, we should use a bit of common sense about how we approach and analyze these situations, to help minimize the hysteria. And, I certainly don’t mean to downplay our need for infrastructure spending. ASCE has been harping on this for years to essentially no avail. But, we may need more spending on bridges, sewers and water mains, etc., not very glamorous, but essential to our economy and well being, and less on new stadiums and the like.

 

[a2mfk]

Makes one of those yellow PVC pipes that hang from chains at the entryway of most parking garages seem really cheap... And I have seen those before bridges and tunnels before.

 

[JAE]

I saw this and just had to post it here.

 

[MJB315]

JAE, I think your photo makes it clear. We should just be happy it wasn't a yellow egg-shooter-downer type of bird...could have been more catastrophic.

"We shape our buildings, thereafter they shape us." -WSC

 

[Archie264]

dhengr,

One quick point: of course ASCE is going to rate our infrastructure deficient; they are hardly a disinterested third party, it is in their interests to do so. That doesn't mean it couldn't be the case, but, rather, simply that they are not in a position to objectively grade such a thing. It's no different than an insurance salesman telling you you need additional insurance or a shoe salesman telling you you need new shoes. Or, to state it in the inverse, it would be akin to a fox rating the hen house security system overdone.

As for the fracture-critical issue, my understanding is that that was brought up by Berkeley professor Abolhassan Astaneh. Per his post on another site he described how this issue was brought up in the mid-1800's and at that time they decided to recommend that bridges be designed using pure trusses, which are statically determinate, but which therefore have no redundancy. This is what he referred to as fracture-critical. According to him the decision was made at that time so that the structure could be properly analyzed and it therefore be known whether the chords were in tension or compression -- and to what degree -- so that they could be properly designed. His argument is that since we now have modern computer techniques this no longer applies and the structures should be designed with some degree of redundancy. I guess that's analogous to the movement towards progressive collapse resistant designs. That is my understanding, at least, and any mistake in conveying his views in this paragraph are mine, not his.