[Towertalk] General Questions about tower strength

[Rick Stoneking]

All,

Have a couple of questions that I was hoping one of the many learned people 
on this reflector could help me with, for my own understanding.

1.  I have a ham buddy who is putting up a 72' freestanding tower and as 
part of the permit process had to have the drawings reviewed and approved 
by a New Jersey PE.  One of the things the PE said was that the size of the 
base had to be increased from the 4x4x7 (or whatever the exact dimensions 
were per the mfg) to 5x5x8 (essentially one foot larger in each 
dimension).  So my question is, what does that do for the strength of the 
tower?  It seems to me that all it does is make it more difficult for the 
entire tower (including the base - intact) to tip over, which seems like a 
pretty unlikely failure anyway?

2. I have heard that the size of the base is such that it would support the 
tower and rated load, at the rated wind speed, even if the base was not in 
the ground (i.e. sitting on top of the ground).  Is that true - always, 
sometimes, never?

3. Does anyone know of a reference source that talks about the windload 
ratings of a crank up tower as a function of the height it is raised 
to?  In other words, if my tower is rated at 50mph winds with 9 sq feet of 
load, at its full height of 67', what is the rating if it is extended to 
half that height?  I believe the rating increases as the tower is lowered 
but I have not found anything authoratitive (or semi-authoritative) that 
discusses this - even at a generic level.

Thanks in advance,
Rick
W2RDS