Poor design led to I-35W bridge collapse?

Say what?!? Unless you're keeping liquid nitrogen under pressure or in a flask, it's going to turn to gas quite readily and quickly. It is doubtful that cement will do its chemical reaction with nitrogen and the aggregate to form concrete.

Perhaps the story is a bit garbled and the aggregate and cement were cooled with liquid nitrogen before the water was added to the mix. Adding liquid nitrogen in any substantial quantity after the water has been added will result in one big ice cube (which won't mix well).

Reply to
Everett M. Greene
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It's what they did. And it worked. It is becoming more common and not shockingly is promoted by the companies generating the liquid nitrogen.

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Reply to
Mike H

That is correct, in that you don't have to seal concrete, as you can just as easily let it all go to hell, or to bird poop (which ever comes first).

If they cut any corners on steel and of the proper servicing of whatever steel, you can bet they cut every possible concrete corner as well. In other words, there wasn't anything in surplus for making that bridge any more so robust than absolutely necessary, if even that much.

Obviously there were significant errors upon errors beyond bird poop.

A good computer simulation of that entire bridge and of its interactive loading should be interesting.

- Brad Guth -

Reply to
BradGuth

And so the combination was an unhappy compromise ? ..in effect resulting in a design that is neither a good vertical support nor a good arch ?

Are not well designed pure steel vertical supports made and in service?

Narasimham

Reply to
Narasimham

In this same newsgroup

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Narsimham

Reply to
Narasimham

No, that method of construction requires more material, and is in fact more expensive to make. But it was:

  • designed conservatively for 4 total lanes of traffic, not 8;
  • to have four operable bearings, not three;
  • to have all of its vertical supports be vertical, not one of them tilted; and
  • to have areas of corrosion repaired, not inspected-to-death.

In the toothpick bridge competition some of us take in our first year engineering class, it is one of the ones that wins.

Arches are simply conservative on material, using the Earth to supply a combined / complex loading. A truss structure simply uses the Earth for vertical support, having handled all the various torques internally (requiring larger cross sections and more members).

True for both truss and arch designs. But they are maintained most places.

Keep in mind this bridge is in an area that (apparently) gets a good deal of mist, generating "black ice", that has had at least two different types of deicers used in its service life. A good candidate for corrosion, and corrosion cracking.

David A. Smith

Reply to
N:dlzc D:aol T:com (dlzc)

Reply to
Narasimham

I 35W over Mississippi River Bridge 9340 August 15, 2007 Bill Kallman, PE

Investigation of Collapse by Kallman Engineering On August 1, 2007 at 6:05 pm the subject bridge completely collapsed, from abutment to abutment. The bridge consists of approach spans consisting of stringers, and a 3-span deck truss over the river. Completed in 1967, this bridge has had major repairs since then, and in-depth inspections since 1997. Two engineering reports, one by University of Minnesota Civil Engineering Department in 2001, and the other by the URS Corporation in 2006 attempted to explain faults discovered in the field inspections made by Mn-Dot for over 30 years. The complete file is found on the Mn-Dot website

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and we have read all of this material and visited the actual bridge site in Minneapolis.

We conclude that the approach pavements on-grade shoved the bridge during the replacement of the transverse joints on the trussed section, hard enough to destabilize the upper chord members, detach the deck, and drop the center span at the points of contraflexure. Less than a second later all the other spans fell towards the river. The very warm weather preceding August 1, 2007 and the deck joint removal defined the timing of the collapse. The "frozen" bearings, cracked and misaligned approach span members, early deck repairs, the tilted north pier, distressed condition of the on-grade highway pavement joints leading to the bridge, all point to severe pavement shove as the cause of collapse.

Quite often, and erroneously so, the phenomena of joint widening in P.C. concrete pavement is associated with traffic loads, age, and water infiltration. NOT SO. As the concrete slabs expand and contract with temperature change, sub-grade material forced up into the joints ejects the joint filler and gradually widens the joint. This causes a general movement of the pavement slabs (downhill usually), often relieving the pressure by "blowing up" at a joint during hot weather. An asphalt repair is then made by a highway maintenance crew to be permanently replaced by concrete at a later date, which in turn increases the shove forces. Any bridge in the way of this pressure will have its bearings displaced. Later the abutment backwalls are sheared off at the bridge seats, decks rotated, and other signs of distress appear.

During my 35-year career with the New York State DOT, a pavement detail was implemented prior to the 1964 Worlds Fair in Queens, NY, where a 5- foot expansion joint was introduced into the at-grade concrete pavement. This joint was ordinarily asphalt on the sub-grade and served well, but required removal the resultant "bump", annually. I recall later lengthening it to 25 feet for ease of construction and maintenance. These joints were called Stress Relief Joints. I know of no experimental work on this phenomena, however measurements of compression within pavement slabs have approached 8,000 p.s.i.. I believe this pavement shove affects many, if not most, bridges and should be eliminated by appropriate details in highway pavement design.

With great respect for the responsibility to our clients - the highway travelers

- who in this case have been killed by our ignorance, I consider it our duty to inform the public of the cause of the collapse, our regret for the lives lost, and our program to see that this doesn't happen again.

Bill Kallman Structural Engineer

310 Mesnard Street Hancock, MI 49930 Phone: (906) 482-5202 Fax: (906) 482-5202 (call first) E-mail: snipped-for-privacy@charter.net CT 16546 MI 41074 NY 40760
Reply to
billkallman

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