Re: Any comments on Minneapolis Bridge collapse?

Thanks for the post, Glen. Your information fits with what I heard
while in the Minneapolis area on business just a week before the
collapse.

What troubles me is that there was great media attention initially
which suggested down-right crooked manipulation/misappropriation of
maintenance funds. It's suddenly been very quiet.

=========================

On Tue, 09 Oct 2007 15:41:06 GMT, Glen Walpert <gwalpert@xxxxxxxxxx>
wrote:


The definitive answer as posted to sci.engr.mech, in case anyone is
interested:

From: billkallman@xxxxxxxxxxx
Newsgroups: sci.engr,sci.engr.civil,sci.engr.mech,sci.physics
Subject: Re: Poor design led to I-35W bridge collapse?
Date: Sat, 29 Sep 2007 13:38:50 -0700

On Aug 3, 12:43 pm, Robert Clark <rgregorycl...@xxxxxxxxx> wrote:
"The bridge must have been near a state of collapse for some time, and
the construction might have contributed to its failure," said Zdenek
Bazant, a professor of civil and environmental engineering at
Northwestern University.

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
http://www.dot.state.mn.us/i35wbridge/history.html 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: billkallman@xxxxxxxxxxx
CT 16546 MI 41074 NY 40760

<www.myspace.com/billkallmanpe>


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