[Marxism] Bridge Neglect

Les Schaffer schaffer at optonline.net
Thu Aug 2 08:23:49 MDT 2007


Joseph Callahan wrote:
>     Does anybody on the list have suggestions for locating reports
> or other info on the neglect of infrastructure, particularly bridges?

The NY Times is running an interesting blog on the bridge collapse:

      
http://thelede.blogs.nytimes.com/2007/08/02/following-the-minneapolis-bridge-collapse/#comment-83454

there is a link to a spreadsheet that lists "Structurally Deficient"
bridges in the US:

         http://www.fhwa.dot.gov/bridge/defbr06.htm

  c.f.  http://www.fhwa.dot.gov/policy/2006cpr/index.htm

There is a 2001 structural engineering report from the U of Minnesota on
the Minn. bridge:

       
http://media.startribune.com/smedia/2007/08/01/21/bridges200110.source.prod_affiliate.2.pdf

the first paragraph of its Executive Summary reads:

    Bridge 9340 is a deck truss with steel multi-girder approach spans
    built in 1967 across the Miss. River ... The approach spans have
    exhibited several fatigue problems; primarily due to unanticipated
    out-of-plane distortion of the girders. Although fatigue cracking
    has not occured in the deck truss, it has many poor fatigue details
    on the main truss and floor truss systems. Concern about fatigue
    cracking in the deck truss is heightened by lack of redundancy in
    the main truss system. The detailed fatigue assessment in this
    report shows that fatigue cracking of the deck truss is not likely.
    Therefore, replacement of this bridge, and the associated very high
    cost, may be deferred.

there was resurfacing of the road, which means small but perhaps
significant changes to *its* structural parameters, a train passing
underneath which yields low frequency forcing possibly matching resonant
frequencies of the bridge, reports of pile driving or jack hammering
(again, low frequency vibrations), and the problems of these fatigue
cracks.

i am holding my tongue on further speculation till i see more
engineering reports. but i heard on TV last nite that the 2005 followup
engineering report warned that the bridge needed to be more closely
monitored for fatigue cracking.

for those interested: "fatigue cracking": take a paper clip, straighten
it out, and start bending it back and forth a number of times.
eventually, the clip will fracture at the spot where you are bending it.
no one bend caused the fracture: the stress stayed below fracture
limits. but the accumulations of bending cycles, often over many years,
allows small micro-cracks to grow into big ones, and eventually cause
catastrophic failure.

    http://en.wikipedia.org/wiki/Metal_fatigue

shall we call for a return of the soldiers from Iraq so we can do the
needed bridge examinations?????

Les






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