MAST STRENGTH

[Richard Thorne - WB5M]

How do you go about determining how much antenna (square foot wise)
you can safely put on a mast.  I know theres an article in NCJ a while
back explaining this but its in storage somewhere.

I have an 18' 2" x .25" wall aluminum mast.  I believe its rated at 
40,000 lbs psi.  Its a good mast but certainly not chrom-molly.

I'm thinking about rotatable dipoles for 40 and 80 at the 7.5' and
15' levels (3' of the mast inside the tower).

Thanks in advance.