Minneapolis I35W Bridge Collapse

It's being discussed ad nauseum on Fox News, but some interesting bits are coming out.  However, some of the questions at the press conference were just plain stupid.  The problem with bridges is a national one, not isolated to a few cases like this one.

My brother was at the Metrodome when it happened, less than a mile away.  He had an employee that was heading for the bridge and got cut-off by someone and had to take a different road.  He saw it collapse and thinks the car that cut him off was on the bridge.

Someone was looking out for him.  I told my brother to tell his employee to hurry up and buy a lottery ticket!

Ned said:

It's being discussed ad nauseum on Fox News, but some interesting bits are coming out.  However, some of the questions at the press conference were just plain stupid.  The problem with bridges is a national one, not isolated to a few cases like this one.

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My favorite question asked by news folk is whether jack hammers caused the collapse. ???   Designs to handle various load types (live, dead, weather, and impact) are computed, then safety factors added. Impact loads are those caused marching armies, for example. That is why they learned to break cadence when crossing the old bridges. If your RV hit a pot hole while crossing, the impact load would be "much" greater than the moving load your rig would cause otherwise. And the impact load caused by a hand held jack hammer would be a pin prick in comparison to the trucks and buses that used that bridge every day.

The chairman of the ASCE (Am Soc of Civil Eng) said today that 1/3 of the bridges in the US have structural problems. And that converts to 600,000 bridges. Not only the bridges -- but the freeway flyovers cause me various degrees of anxiety according to their height. Every time I drive over the really tall one taking me from the 5 freeway when driving South to the 14 freeway over to Palmdale I just take a deep breathe and pray. That's one that "did" come down from an earthquake - and no one will convince me that another quake will not topple it again.

Did you see the security camera film of the collapse? Amazing footage that will surely help a bunch to determine cause. The entire trussed span over the river came down together. The East end "did" come down first, appearing to rip the West end from it's abutments. I'm betting on fatigued steel members over the East abutments.

Maybe it is about time we start taking care of the US needs and slow the outflow of US dollars to other countries.  Looks like it is past time to start fixing things here.

Don't wish to appear political, but you're dead right there Ron. OTOH we've alienated so many folks outside our shores that we don't really have any choice any more. I recall the days when we could turn up at an airport and it was like a bus station. Those days are gone forever.

I wasn't trying to be political either just expressing what I believe would be common sense.

I know Ron. I was merely clarifying my position.

I was taught in my very young life that one cannot buy friends.  From what we see in the world today that is just being proven over and over.

Ah, they don't build them like they did in the old days/old country. A few photos of bridges near the village of Pontrhydyfen at the north end of the small valley where I grew up, known as the Afan Valley in South Wales. The first two photos are courtesy of the late Dave Mitchell, BIL of an old school friend and yours truly respectively. For the linguists, the Welsh equivalent of the WiKi is here.

• The stone aqueduct that leads across the valley to the birthplace of deceased actor Richard Burton.
• A brick railroad bridge less than a quarter mile away.
• How about the Pontcysyllte Aqueduct, designed by the legendary architect Thomas Telford. A 1,000 foot-long structure built in 1805 over the River Dee in North Wales.

Note, in each case, the arch structures in continual compression that Bob talked about. All structures are in use to this day.

You hit the nail right on the head there.  In Ecuador we seen some aqueducts still in use that were built before the Spaniards got there.

One of the subjects I studied in college second time around used the book The new science of strong materials "or, why you don't fall through the floor", as one of it's lighter texts. I never really bought into some of the concepts, which might explain why, when it came to structural model building, I flunked.

There is a reason many older structures such as bridges are still standing and newer ones fail. I recall the 1st few days of one of my Structural Design classes the professor brought up that very thought -- and used the Brooklyn Bridge as one example (now over 100 years old). Engineers of old had two advantages -- (1) concrete, rocks, steel, and labor were cheap and (2) the concept of the arch had been invented. As a result, they could throw as much concrete as needed around arched spans to make sure they would virtually last forever. Later engineers do not have that luxury. If the material used in the Brooklyn bridge were bid today -- they would lose the bid. As would the builders of the pyramids.

When the Grand Coul?e Dam was built, concrete and steel were cheap -- so a "Gravity" dam came from the designers. The concept is if you pour a huge wall of concrete wide enough and tall enough -- no amount of water will make it turn over, and it for sure ain't gonna leak. That design has since been replaced with thin shell arched dams. Turn an arch on it's side and you have a dam. The concept is the same in that no matter where the load is applied across the span, it will be distributed into the abutments. An example is Hoover dam in Las Vegas. And if the canyon is too wide, Reclamation became the innovators of the earth fill dam. Those span the Trinity River, the Oroville Dam on the Feather River, and the long canyon of the San Luis reservoir. "No One" builds concrete gravity dams anymore -- but the ones that "were" built will outlast the pyramids.

That professor made the point that in today's world, the engineer that gets the bid must, thru better design, come up better structures such as bridges for far less monies. Governments cannot afford mass concrete and steel bridges anymore. However, he also gave some words of caution:

"When a doctor makes a mistake, they bury it. When a structural design engineer makes a mistake, they have a mass funeral."

Bob, I know you're an old civil engineer, so if it looks bad to me (it does), it must look awful to you because you actually know what to look for.  I wouldn't be surprised if we've gone across that bridge as I'm sure others in the group must have done.  Our interstate system is aging and a lot of the bridges are being replaced as we saw both last year and this year during our travels around the country.  Jerry and I often comment about various bridges in poor states of repair.  Doesn't make us feel very good about crossing them in a large vehicle.

Bet we will all think of this when we drive across bridges for some time.

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Ron, we went across a bridge this evening and commented on it.  These images stay in our brains for a very long time.

Following the 1989 Loma Prieta earthquake in the San Francisco Bay Area, I "think of this" every time I go under a freeway overpass. If traffic comes to a halt, I try not to be stuck under the overpass, but sometimes there's no alternative and I can't wait to get out from underneath.

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Tom, you're not alone.  And not just in California either.  There are earthquake faults in every state and I try to stay away from being under or on any bridge for very long.  I just can't help remembering our Bay Area bridge collapses.

ArdraF

Another element is not only the design but the actual construction.  What happens when the contractor buys off the inspectors to approve shoddy workmenship which may not show up till some time after completion.

Good points regarding the amount and prohibitive cost of materials Bob. Understood the arch on it's side from having viewed documentaries on Hoover Dam. A colossal amount of concrete went into that project.

When we've crossed some bridges or been in some buildings, even ones in good/new condition, Chris has often heard me say "I hope the engineer who designed this got his sums (math) right".

How many of those old bridges are carrying 8 lanes of heavy traffic?

Bob, the bridge runs north and south.  The south end apparently gave first, then the whole span dropped.

Also, see this article for some statistics on how many bridges in MN and the US are similarly rated.

One of my news aggrators today said that they saw the first signs of problems with that bridge as early as 1990, yet in 17 years nothing has been done, NOTHING.    Someone clearly needs to answer for this.

Alas, even if they do identify the responsible person and bring him/her to justice it won't be enough. It can never be enough.

Has anyone been in contact with Sarah?? I don't know that she even goes near that bridge but it would be nice to know she's OK. I'm sure someone has her number.

Looking at photos of the collapsed section in the river, I noticed that the lane closures for the repaving project were asymmetrical.  Instead of shutting down the two inside lanes on each side of the bridge, or the two outside lanes, the contractor funneled all traffic into two outside lanes on one side and two inside lanes on the other. 

Two of the open lanes overhung the width of the truss.  On the opposite side, the overhanging lanes were vacant, being repaved.  See the picture here

If the bumper to bumper commute traffic was on the side with the traffic lanes on the outside edge, you'd have high twisting forces on the span.
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We can blame ourselves, too. We want things cheap. We want low taxes. We don't want the inconvenience of highway lanes being shut down for repairs. We want more for less. And we want to blame someone, anyone, except 'us'.

JMO
Wendy