[TowerTalk] AB-105 Diagonal

[Frank Donovan]

Hank,

There were three versions of the AB-105 tower, the most
recent production was AB-105C.

Diagonals for AB-105C were constructed from 1 1/2" by
3/32" steel strip, stamped into a 90 degree angle, except
at the ends where the diagonals attach to the tower.
AB-105C diagonals were marked G-8A and G-9A.
My micrometer measures 0.10 inches diagonal thickness,
because of additional galvanizing thickness.

Because the diagonals are critically important to AB-105
strength, all military contracts for AB-105C required
compressive load testing of the diagonals (on a random
sampling basis) to 1700 pounds compressive load.

The much older G-8 and G-9 diagonals used on 1950s
era AB-105 (not AB-105C) were fabricated of thinner steel
plate were not subject to contract requirements for
compressive load testing.  I always destroy any G-8 and
G-9 diagonals I might encounter.

Here are the performance specifications for AB-105C tower,
from the current manufacturer, Penntech International:

Max practical height with no additional loads:   280 ft
Max allowable bending momant at tower top:    20,000 ft-lb
Max vertical guy span under max loading conditions: 35 ft
Width of tower face between CG of legs:   22.59 inches
Projected area of one face per lineal foot of tower:  0.5513 sq ft
Wind pressure per lineal foot of tower:   27.99 lbs (RS-222A no ice)
Radius of gyration (least) of tower:   9.04 inches
Cross sectional area of one leg:  0.603 sq inches
Moment of inertia (least) of tower:   147.76 inches**4
Distance from center of tower to CG of leg:   13.04 inches
Section modulus (least) of tower:   11.33 inches**3
Section modulus of one leg:   0.171 inches**3 (least)
Radius of gyration of one leg:   0.560 inches (least)

Let me know if I can be of further assistance.

73!
Frank
W3LPL
donovanf at erols.com


----- Original Message -----
From: <kr7x at comcast.net>
To: <towertalk at contesting.com>
Sent: Thursday, August 05, 2004 5:41 PM
Subject: [TowerTalk] AB-105 Diagonal


> Hello TowerTalkians:
>
> I need a favor from the list:
>
> I'm in the process of determing the capacity of and AB-105 tower for a
building permit. I have a copy of the old TM for the AB-105 but the
cross-sectional shape and dimensions of the diagonal members is called out
2 different ways with different dimensions.
>
> I can determine that it is 13 ga. but the cross-sectional shape and
dimensions are in conflict. Could a owner of such a tower please measure the
diagonals for me. I need verification of the thickness and the dimensions.
Is the shape stamped into a V , or an L or a U or what? A sketch would be
appreciated.
>
> Thanks for the help.
>
> Regards
>
> Lonberg Design Group, Ltd.
>
> Hank Lonberg, P.E., S.E.
> President
>
>
> _______________________________________________
>
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>
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