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deck collapse, part IX

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How did I know two sentences in to your response it was you Scott? You have
quite the distinctive style. Also when I know I cannot see your name without
scrolling down it must be you. Have you been on vacation? Perhaps a canoe
trip on a lovely Michigan river? If your engineering and teaching career
ever get boring there is definitely law school or politics. Just joking,
mostly :)

I think I may have been misunderstood, but I was basically assuming an
engineer was not at fault in the design. That may be jumping the gun,
because you brought up lateral loading, or sway bracing. Although even
without diagonal braces, a deck is usually braced through diaphragm action
via the deck to the ledger, and the stair, but this is one possibility. But
it seemed the mode of failure was not through what you would expect from
sway, it was more of a vertical, "pancake" type collapse. I still contend
there is no big hurry in getting such a disaster immediately cleaned up. I
would think you would want at least a few engineers each investigating, so
you get different opinions. It is hard to pick a failed connection out of a
pile of rubble. I am sure we have all done a bit of forensic or diagnostic
engineering, and that is usually the most difficult. I have never done
anything on a full scale collapse where all you are left with is a pile of
rubble, that has to be very difficult to figure out.

But you have a point Scott, we should not jump to conclusions. It is a
little sad about WTC victims' families not understanding the collapse being
cleaned up. It doesn't take a structural engineer to figure out that we do
not normally design buildings for jet airliner impact. Nor do the MEP guys
design sprinklers and ventilation systems for large amounts of jet fuel.
Think of how many lives would have been saved if all of the towers would
have been immediately evacuated. ( I don't know if the answer is airport
security, but it seems more logical then designing every building to be
jetliner proof.)

I think it must be a sign, but I am sitting down late last night for some
dinner and flipping through the TV I find ENGINEERING DISASTERS on History
Channel. (Timely scheduling?)  This is part of a series, so check your local
listings, it is GOOD. Also makes you a little uneasy as an engineer.

Mainly civil/structural failures, but also electrical and mechanical. THere
was a dam north of LA that originally supplied LA with water, which the day
after being inspected by the "architect/designer/builder" (this is in the
20s), who gave it a clean bill of health, collapsed killing 400+ people. The
guy lived the rest of his life in remorse and in recluse.

The lift slab technique of building slabs on the ground and jacking them up
into place- that led to a pancake type failure during construction in CT ,
killing 30+ workers. I think that was the worse single construction disaster
in US history. CT banned this type of construction and everyone else pretty
much dropped it. THere was a huge pile of rubble to sift through. Turns out
a small steel wedge slipped loose that held the slab to the jack. That just
shows you how one tiny detail can cause the whole structure to fail. One
little hanger connection could have failed the whole deck....

I may have mentioned this on the list already, but I highly reccomend the
book, "Why Buildings Fall Down". It actually highlights a lot of the
disasters on this show. It even discusses the aeronautical structural
failures of the first jetliners, the British Comet. It relates to us because
it is a material fatigue stress failure at a window, a natural weak spot on
any structure. Anyway, this book is light and easy reading for a structural
engineer as it is written for the lay person. Good reading for a friend or
family member who wonders what we do all day. (My dad actually bought it for
me. I have passed it to the other SE in the office and he really enjoyed it
too.) Since most of the structures discussed in the book were a bit more
then I will ever design (bridges, dams , stadiums), it was a good learning
experience for me. The main thing you learn is it is all about HUMAN ERROR.
Whether from a load perspective, code enforcement, miscalculation, poor
coordination, using unproven or the wrong materials, poor maintenance and
inspection, or poor construction, it does not matter how many computers we
have, it is still up to us. Also, connections and redundancy!!

(Then I also saw a special about Rome the other night and they showed a
stone bridge they built that is still being used- not just standing. They
did not pay the builder for 40 years to gurantee it had been done correctly.
Do you think the Romans had STAAD or AASHTO guidelines? They did not have
the wheelbarrow, compass, or level.)

Well, I guess that is enough speculation, and like Scott smartly suggests,
sit and wait for all the info. I will still bet someone it is a connection
failure...


I hope everyone has a safe 4th, keep the number of people on decks low, and
stay away from large trucks of fireworks (4 people died down here in FL
yesterday).

Andrew Kester, EI
Longwood, FL






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