[TowerTalk] The last aluminum mast comment

[Ed Jensen]

Hi Steve,

You wrote:

>  I think that you forgot to multiply by the wind pressure. At 70.7 MPH,
it's 20 psf, 80 > MPH is about 25 psf. Your analysis doesn't allow for the
load
> distribution up the mast. (Sorry, I'm not an engineer.)

I wrote:

>>  Antenna                             area (sq ft)    load (#) (@ 80mph
using  25#/sq ft)
>>  TH7                                         9.4                  235
>>  Disc1 (40m 1 el)                    2.7                  68
>>  214FM (2m 14el)                   1.7                  43
>>  WARC 2/2 (12/17m yagi)     3.1                  78
>>  mast                                        .1/ft                 2.5/ft

As you can see Steve, I did multiply by the wind pressure (25 psf).

My distribution again was:

>  Antenna      area (sq ft)      Hgt above tower(ft)    bending moment
(ft#)
>  TH7               9.4                .5
118
>  WARC 2/2     3.1               5                                   390
>  Disc1          2.7                 10
270
>  214FM        1.7                 12
516
> mast             1.2                  6 (avg)
180

Note that bending moment is calculated from areaXwind pressureXHgt above
tower.  So I did allow for load distribution up the mast.

The load WILL be supported.  Try the MARC program (I don't have it) with the
antenna distribution I posted and let me know the results.  Placing the high
area antennas close to the tower makes a big difference.

73, Ed

Ed Jensen, K5ED, El Paso, TX, k5ed@dzn.com




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