Re: Application of algebra

In article
<443d301e-54f0-41bc-814b-fe68b3c0dd78@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Jim Wilkins <KB1DAL@xxxxxxxxx> wrote:

On Jun 5, 2:33 am, Bruce L. Bergman
<blnospamberg...@xxxxxxxxxxxxxxxxx> wrote:

  The original design had multiple hanger rods going to the roof, one
for supporting each layer separately from the rest, and a specifically
designed saddle to hang them from.

  The builder used one rod to hang the top bridge, then a second rod
from the top bridge down to the second, and then another from second
to third.  And he modified the mounting method so one set of rods and
nuts on the top level was carrying the entire load of all three
levels.  A disaster waiting to happen.

  --<< Bruce >>--

IIRC from his talk to our Mensa group a long time ago, the accident
investigator said that the designer specified one-piece rods running
through all levels with threaded sections for the walkway support nuts
and the rest turned down. The cross-section of the rod was large
enough for the entire load but the threads were sized to carry one
level only. The builder didn't have the floor space around his lathe
to turn rods that long so he divided them into sections with coupling
nuts.

I remember progressive thread failure caused by the bolt and nut
stretching unequally from somewhere, possibly this lecture, or an
article on Herreshoff the yacht designer who made his own turnbuckles
so carefully engineered that samples tested to failure were distorted
all over.

I have the accident report somewhere.

The architect's mistake was to specify a very long 1.25" (?) diameter
stainless steel rod with threads in the middle, in three places, where
the nut holding the three or four decks would be. The threads would
need to be larger than the rod, so a nut could be slid along the
unthreaded parts. However, one cannot buy such a rod.

The construction company's main mistake was to try to build it anyway,
with field adjustments to the design, rather than insisting that the
architect come up with a practical design.

The construction company's other mistake was to fabricate the box beams
underlying the decks from two channels welded flange to flange.

As Bruce described, the replacement design tripled the load on the nut
holding the the top deck, and the nut simply pulled through the
fabricated box beams, forcing the channel beams apart by ripping the
welds. Once one nut pulled through, the impact caused most of the
others to also pull through, and the whole thing just unzipped.

Joe Gwinn
.

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