On 7/8/19 8:20 AM, Wilson Lamb wrote:
I wouldn't want a neighbor's tower/Yagi looming over my backyard...and I love
towers!
The fall zone idea seems like simple good manners.
Good manners, but impractical in a lot of cases, and not really
necessary - assuming most of the guys remain intact, it will tend to
drop in a heap.
I have been loosely involved in dropping 200' BC towers, dropped by cutting
the rods at one guy anchor, thus losing all guys on that side.
They fell absolutely full length, with a few sections not even bent!
I think a foundation failure (soil, bolt, gin pole) would drop a crankup to
full length.
Is there any experience available on this?
Full length failures are actually unusual. Most tall skinny structures
will tend to buckle in the middle as they fall - as it falls, the linear
acceleration of each small segment is determined by the force of gravity
on that segment, which is the same for all segments. But, if it's a
rigid body, the acceleration has to be greater at the free end than the
pivot end. So there's an overall bending force on the "rod", and that
force rapidly becomes larger than the buckle force.
Now, it could buckle, and then straighten out when it hits, sort of
folding and then unfolding, but apparently, that's unusual.
"La Mirada, CA- “On Sunday, December 19, 2004 at
9:45 a.m. PST Jim and Mary Ghosoph were killed when
their rented Cessna 182P single engine airplane,
travelling from the El Monte airport to Fullerton
Municipal, struck KFI's transmission tower. The solid
steel truss, originally built in 1948, collapsed upon itself,
falling primarily into a parking lot north of the site. The
crash occurred on a sunny, cloudless day.”
https://arxiv.org/pdf/physics/0210033.pdf has an analysis and some
examples using toy blocks.
from 1918, Scientific American, a picture showing the brick chimney
clearly bending as it collapses.
https://books.google.com/books?id=xbsxAQAAMAAJ&pg=PA83&lpg=PA83&dq=scientific+american+chimney+collapse&source=bl&ots=KlHL61oOWJ&sig=ACfU3U0WWk_RtAhiQVJmJ2LybBleULuNfg&hl=en&sa=X&ved=2ahUKEwjakI-t66XjAhWHsp4KHS2NBKMQ6AEwCnoECAgQAQ#v=onepage&q=scientific%20american%20chimney%20collapse&f=false
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