At 07:56 PM 3/14/2006, Bruce Ferratt wrote:
>Hello and thanks for letting me post a question.
>How strong is a solid aluminum mast compared with a walled/hollow mast?
almost all the strength for a round member comes from the outside.
Consider bending.. the maximum stress is at the edges
For torsion, the derivation is a bit trickier, but it's the same
So, to answer, for the same weight of tubing (which is how you buy it, by
the pound), the tube is stronger than the rod.
it goes as od^4-id^4
>I secured a solid, round 12' aluminum mast 6061-T6511 grade. What is the
>likelihood of bending when loaded with a TM-33A and VHF 2m/440 vertical at
>a rated 70mph wind load in Northern Virginia? 8ft of mast will be exposed
>above the point of the tower peak (Rohn 25G), with about 4 ft inside the
>tower to rotor plate.
That must weigh a bit!... You forgot an essential dimension: the diameter
of the mast, and the cross sectional area of the antennas. Ballparking, a
load of about 300-350 lbs at the end will bend a 2" solid bar 8ft long.
There is an old QST/QEX article around that goes through the calculations,
and I think there is a spreadsheet that accompanies it, either on the ARRL
site, or maybe K7LXC's site?
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