[TowerTalk] Tower Collapse in South Dakota

[Rob Atkinson]

>I believe that the reason it laid down full length is because it had a pier
>pin and the pin sheared when a guy let go.  If the base had been cemented in
>(all 3 legs) like the majority of ham towers, it would not have failed like
>that.  I would have crumpled in, twisted.

Professionally constructed guyed lattice towers are always on pier
pins even if a base insulator isn't needed.  No commercial guyed tower
is ever put in the ham way of sinking the legs in concrete because the
tower has to be able to turn without twisting, because twisting will
cause a failure.  Hams seem to think that if their 100 foot R25 tower
loses its guys, it will stay vertical because the base is sunk in
concrete.  You can't treat a uniform cross section guyed tower as if
it is free standing.  The only reason hams get away with that business
of sinking the legs in concrete is that the majority of guyed ham
towers aren't very tall relative to face width and aren't heavily
loaded.  Any guyed tower hundreds of feet tall will _never_ be sunk in
concrete; they have to be on a pin or they won't survive.  The pin
likely helped the tower stay up at least at first, because the added
wind loading caused by ice added to the turning force.  If it had been
twisting with ice it would have collapsed a lot sooner.

73
Rob
K5UJ