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RE: 'Epoxy creep' factor in Big Dig death

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David,

	Did you look through the slides in the link that Drew sent? The
NTSB addressed installation problems in those slides. There were some
problems, but they didn't seem to be the root problem. As for your
comment why didn't more panels fall if creep was the issue, take a look
at some of the post accident inspection pictures. More of the epoxied
rods were pulling out. Time would likely have brought more panels down.
There is a very interesting graph on one of the slides that shows the
difference between the displacement over time of the fast set epoxy used
and the normal set epoxy. If the normal set epoxy had been used creep
maybe wouldn't have been an issue.

	I am not trying to blame the engineers. In their place I might
have done the very same thing. The problems associated with long term
loading do not appear to be well documented. If fact in the ICC report
there is a statement that the epoxy is suitable for supporting dead
loads. Nothing says that this applies only to normal set epoxy or only
to shear loading. 

	I would be very interested to hear what some of the engineers
who work for epoxy retailers have to say about the testing their
companies have done related to long term loading. Have they done long
term tests? Do their products fail over time? If there is problems with
creep does their product literature clearly state this?

Wesley C. Werner 




-----Original Message-----
From: David Fisher [mailto:dfisher(--nospam--at)fpse.com] 
Sent: Wednesday, July 11, 2007 10:00 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: 'Epoxy creep' factor in Big Dig death


This was certainly a terrible tragedy.

But, as I understand it, epoxy anchors typically have a safety factor of
at least 4:1.

If it were really "epoxy creep" then why didn't more panels fail?

I guess my point is that maybe the installation was faulty; perhaps the
hole was not cleaned out or the epoxy incorrectly applied, etc.


I think we can all look back at details we've done over the years and
wonder "what was I thinking?"

I think it could be classified as "seemed like a good idea at the time"

Obviously, some sort of redundancy should have been built into the
design; but say the panels were supported by four rods; at 4:1, the
panel should have only needed ONE rod to support its dead weight...at
least the panel would have come loose and repairs been able to be made
to stabilize it prior to failure.

It appears that there might be more to this story...


Still, an awful waste of human life.




David L. Fisher SE PE
Senior Director

Cape Cod Grand Cayman Holdings Ltd. - Cayman
Fisher+Partners Structural Engineers Ltd. - Cayman
372 West Ontario Chicago 60610
75 Fort Street Georgetown Grand Cayman BWI
319 A Street Boston 02210


312.573.1701
312.573.1726 facsimile
312.622.0409 mobile

www.ccgch.com
www.fpse.com







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