[TowerTalk] Fall Zone

[jimlux]

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