Engineers blame gusset plate failure.

Gore blames mankind.

Media will run with ... ?

The "so-called" gusset plates?

I noticed the "so-called" as well. Bizarre.

While its fun to speculate (and it also helps to sell newspapers and advertizing), I again caution to wait for the final report.

Although, they do raise a good point...don't store 100 tonnes of gravel on bridge decks! Yes, yes, we should let everyone know about that...also, another good tip is not to fly jumbo jets into the substructure...oh and how about, don't detonate high explosives within 3 feet of a bridge.

Good grief! 100 tonnes!

I agree with eyeore, you wait for the final report, but this stuff gets released for a reason. The engineers clearly feel this was a factor and want to make sure precautions are taken before the final report.

100 tonnes of gravel on a bridge, we sure do trust previous builders.

eyeore said "...also, another good tip is not to fly jumbo jets into the substructure...oh and how about, don't detonate high explosives within 3 feet of a bridge."

Don't pee in wind, dont tug on Superman's cape.....maybe jim croce is the answer to everything....:->

The engineers will do their job and figure it out.

"So called" probably means that the part/plate in question has a proper technical name, but that its commonly known name is "gusset plate". Either that or the journalist was lazy with something.

Any thie I see public structures (built with public funds or subsidies) collapse I have 2 suspect causes I want cleared before I ascribe supernatural abilities to structural steel to either melt like butter by the sun or a short low intensity fire.....I need to know:

1) Where substandard materials used in construction by contractors skimming for profits

2) Was there regular maintenance and if so were sub standard replacement materials/methods used by contractors skimming for profits.

3) If it was sold to a private concern, who owns it now, what was the investment on the sale and what is it insured for?

If those 3 inquiries turn up no anomalies..then by all means check to see if steel melts like butter under low heat exposure

For those who don't know, one of the rituals that Canadian engineering students pass through at graduation is the "Iron Ring" ceremony. Each student is presented with a small iron ring to wear on the little finger of their working hand.

The purpose of this ring is to serve as a constant reminder that our work will be used by others, and it demands a certain humility from us. Errors in our profession can lead to the death of thousands; all of us thank God that the toll in Minnesota was far lower. I won't say that vain and boastful engineers don't exist; I will say they are a very small minority.

I'm not a civil engineer, so I can't comment on whether the tests or evaluations of the Minnesota bridge were adequate. But, as a telecom engineer, I know that our basic rule is: "Make sure it works". We always design in multiple backups and redundacies, and try to avoid "single points of failure" at all costs.

For example, if a new financial services firm was setting up in Calgary, I would not only recommend getting phone and data services from two companies but also that the physical routes employed by the two were distinct (so that one incompetent backhoe operator can't cut off all communications in a single stroke). And we can see this ethos in the design of Minnesota's I-35.

There were two distinct spans; if one failed, there was another to be used. Was service degraded? Yes. Was service denied? No. In the biz, we call this "graceful fallback".

However, graceful fallback seems both hollow and mocking to the people who suddenly felt the road beneath them give way, and experienced a sickening plunge towards death. The only solace I can find from this event is that the death toll was so low, and to that, I doff my cap to my civil engineering brethren who doubtless designed the bridges so that failures would result in minimal loss of life.

I post this to let all SDA readers know that engineers take our responsibilities seriously. I also frequently post here challenging the "AGW" hypothesis. As an engineer, where we live and die on cold hard facts, the AGW fiction doesn't cut wood.

As KevinB points out there is a ritual of calling for engineers in Canada. The ritual was developed by Kipling who also wrote several poems about engineering. My favourite is the Hymn of Breaking Strain. If I can quote my favourite verse:

We only of Creation
(Oh, luckier bridge and rail!)
Abide the twin-damnation -
To fail and know we fail.
Yet we - by which sole token
We know we once were Gods -
Take shame in being broken
However great the odds -
The burden or the Odds.

Ah, if I could write that well I wouldn't need to be an engineer!.

In regards to the bridge failure, it is good to get the warning out, but I would need to see a lot more information before I could do any calculations. However Eeyore I think says it best: don't store 100 tonnes of gravel on bridge decks. ........ Good grief! 100 tonnes!

with the "failure" two things came to mind when read that there was "work going on

1) one was eguipment and material loads, and were they were placed, possibly focused and to close to one critical point, rather than spread out

2) was there vibration factor, such as "jack hammers",which there was

those two points, and trought in some degradation and/or design problems, mix properly and you have the recipe for disaster. The vibration effect is what is often forgotten or ignored

Kevin

I am not an engineer. I tend to disagree with you on the ratio of "arrogant jacka$$es" to reasonable engineers:-)))))

I know that 100 tonnes sounds like alot of mass. And it is if it's concentrated on a point. But let's remember it's gravel and being stored on an operating bridge. So it's foot print would be ridgidly constrained.

Based on this picture of the bridge (http://delivery.viewimages.com/xv/75930889.jpg?v=1&c=ViewImages&k=2&d=17A4AD9FDB9CF193C5C774F586F182D5CCE61346298DFA124C9A4FB5D0EE306D) it is a 4 lane bridge (2 each direction).

The typical lane width of a US bridge is 12 feet (3.66m)

Assuming they closed 1 lane for laydown, this would give them a max gravel pile width of 3.66m. A typical internal angle of friction for gravel is 30 degrees. So the pile could only be 1.06m high.

A typical unit mass for dry sand and gravel is 1680 kg/m^3. So 100 tonnes of gravel would have a loose volume of just under 60m^3.

Using the cross-sectional profile above, the length of the gravel pile would be 30.8m.

Now if you take the footprint of the gravel pile (30.8m x 3.66m) it has an area of 112.7m^2.

Taking the weight of the gravel pile (100 tonne = 981 kN) and spread it over the footprint, the gravel exerted a pressure of 8.7 kPa (1.2 psi).

This is a very non-extreme value for pressure. Now I don't have a copy of the Canadian Bridge Design Code but I do have the National Building Code. So just as a sniff test when designing a garage or parkade if it is to take loaded buses and trucks you would use a "use and occupancy" load of 12 kPa. And that's just 1 load of many that would be used in the design. Add to that things such as snow & rain, wind, etc and the actual design load is much greater. Considering that this was an Interstate Highway bridge I imagine it was designed for larger loads.

One of my favorite Sayings from the Old Days of Engineering School was this, from a great Engineer and Great Teacher and Soldier named James McFarland Brown...
In speaking about a BSing fool:
"That idiot does not know whether his ass was punched or bored!"

I think that would apply to most reporters and news writers and it certainly applies to the people who are trying to make this an environmental story!

What’s the big deal about 100 tons of gravel? That’s about 2 ½ semi trailers filled with Diet Coke.
No wonder Moore, Gore, Suzuki etc. find it so easy to stampede the voting public towards a cliff. They merely have to throw out some numbers about things that most people have never before put a serious thought to.

If it is a problem with the gussets, then they should take the spammers advice and make them longer and thicker.

Per Kevin's and Reid's comments, bridges have two types of loading at all times - the static (or dead) load of the structure itself as well as dynamic live loading. Dynamic loading comes not only from the traffic that travels over the bridge, but also through the ground (vibration due to traffic from areas adjacent to the bridge) and via wind loading. Add the disruptions (and vibrations) caused by construction, and it could be ventured that weakening due to stress cracks, rust, etc could be exacerbated. Not having the blueprints of this bridge handy, not access to detailed reports, I'm just taking some guesses here. An extra static load of 1.2 psi is immaterial, especially compared to the 2400 kg/m3 (average) for concrete.

Consider that the bridge itself was constructed in 1967. Traffic profiles were vastly different then. Most heavy cargo was still being transported by rail, while transport trucks were both smaller and carried lighter loads. Cars were heavier, but there were also fewer of them because the population of MSP was smaller and fewer people had as many cars as members in their households. It all adds up - trust me, I've done the math - very quickly. In the end, there are too many factors that need to be taken into account to come to a snap conclusion. They will likely find that it was a combination of factors that contributed to this collapse.

Very interesting thread. First and foremost, I agree with Sylia, it was likely a series of combined factors that caused failure.

None the less I will still make an argument for this pile of gravel to be significant. In regards to the weight, taking Cal's weight equivalent of 2 1/2 semis, we need to look at the length of a semi. A typical semi is about 53 feet (about 16 meters) so 2 1/2 would have a combined length of over 40 meters. However as Reid said, the pile was spread over 30.8 meters. So it does seem to be on the high side. In addition if the pile was in a cone, the maximum weight would be in the centre of the pile.

Would these cause high enough stress to cause failure by itself, of course not, but I think it could be a contributing factor.

Regards,

John Cross:

A further picture I found (http://newsimg.bbc.co.uk/media/images/44034000/jpg/_44034283_slope220ap.jpg) shows that 2 lanes out of 8 (the first picture I looked at lead me to believe that it was less lanes) were closed and under construction. However, my assumptions of the gravel pile dimensions are still valid. If 2 lanes were closed only 1 would be used as laydown as the other would be needed to allow equipment and people to move around.

the problem with your hypothesis of a "cone" is that it doesn't take into acount the geometric constraints. To have a "cone" and maintain a slope angle of 30 degrees the diameter of the pile at the base would be 9.3m. Or 2.5 lane widths.

The gravel would have to have been placed in a long, triangular, narrow, low pile. And thus the effects of concentrating the load at the centre are minimized.

I actually think the semi analogy is a very appropriate one.

Half of the bridge was shut down for maintenance.

Construction machines and materials on one side,
Stalled traffic on the other.

Could have been loaded near capacity.

Lotsa variables to look at and weed out.

Materials testing on failed gussets, beams, concrete.
Design load factors vs. actual load at failure
Did a pier shift?

Glad they don't make up like that anymore.

Reid: Good point about the cone. In regards to the two lanes, that brings the load down, but it is still significant.

John

Was it not Paul Anka who wrote, "Gusset doesn't matter any more"?

I doubt they used "45 lb jack hammers" to remove two inchs of decking.

Those are small hammers that can be used by one man horizontally.
They are on site to expose the rusted rebar in the concrete handrail and other hard to get at places.

More likely they used jack hammers on bobcats or front end loaders to break up the decking.
Or more likly had a resurfacer grind it off.
45 lb hammers would'nt vibrate the bridge much at all in comparison.

Most hand held jack hammers used to break concrete on road/bridge jobs are 100 or 120 lbers.

Those gussett plates are found in places that inspectors can't or won't always climb to and inspect.
I have seen those plates corroded and warped with 2 inches of hard rust and no rivet heads.

Two maintenance cycles of blasting and painting those plates without the proper inspection and replacement and boom.

See this latest from teh reference frame. Scientific fraud by the warmenizers - holy cow.

http://motls.blogspot.com/

john & ried

first off, I doubt that they would loose pile gravel in a work area such as a bridge

second, the load, no matter how distributed, is carried through the support points in it's entirety, thus if it is placed closer to one point than the other, that point will carry more of the load

having worked in construction I'v been privileged to see how everyday workers often have NO concept of how and what they effect with their actions

One thing I've learned in my Flight Safety Accident Investigation days was to let the evidence do the talking and don't investigate based on any preconceived theories.

For my personal two cents worth, I agree with several of the commentors here that it is more than likely a series of events/reasons that contributed to the eventual collapse.

> Not having the blueprints of this bridge handy, not access to detailed reports, I'm just taking some guesses here.

Please, all of you: Stop guessing. Go educate yourself.

http://www.dot.state.mn.us/i35wbridge/history.html

Becarful of LIQUID LIGHT it san desolve anything but a few elements and SUPERMAN