Windloading questions

[Rick, K7GM]

     I am starting to put up a real tower and antennas and a few questions
have come to mind which undoubtedly have answers somewhere among the
multitude of Reflector users.
     For various reasons, I will probably be putting up a 72' crankup
(US Tower or equiv) with a 3 ele 40 (probably) on the bottom and a
tribander (such as a KT34XA) up 10 feet or so.  The tower is rated
at 30 square feet in a 50 mph wind.  I'm sure that is 30 SF at the
top of the tower (or, maybe, 2 feet up).  Obviously, a KT34XA (9 SF)
which is mounted 10 feet above the top of the tower has a windload
in excess of 9 SF on the tower.
     My questions are as follows:

     - What is the windload of a 3 ele 40 by KLM?  What is the
       windload of their 2 ele version?  I can't find anything
       on this.
     - Is there a handy formula to determine the windload at the
       top of the tower for an antenna mounted X feet up?
     - Should I enlarge the concrete base if I do this?  I guess
       I'm really asking whether the weak point in such a setup
       is the base or some other tower part.  This question assumes,
       obviously, that my configuration would exceed the 30 SF
       limit.


                      Rick, K7GM/4
                      aoniswan at ecuvm.cis.ecu.edu