[TowerTalk] AB-105 ratings

donovanf at starpower.net donovanf at starpower.net
Thu Oct 4 16:19:48 EDT 2007

Hi Carl,

AB-105C strength should be about midway between Rohn 55 and 65.  As a rough approximation, the relative strength of a well engineered tower is a mainly a function of face width and weight per unit distance of tower height.  

AB-105C is somewhat stronger than the earlier AB-105 versions.  You
can identify AB-105C by the part numbers stamped in every part.  
AB-105C part numbers always end in "A."   For example, the part number
of ten foot AB-105C legs is G-4A, and G-4 for older versions.

Below are the engineering specifications for AB-105C from the current
manufacturer, PennTech Tower.  I do not have similar engineering data
for Rohn 45, but be assured that AB-105 is much stronger. 

Regarding the vertical span between guys, although 35 feet is specified for maximum tower strength, 46 foot span provides only
slightly reduced strength for towers less than 150 feet tall. Vertical
spans greater than 46 feet begin to significantly reduce tower strength because of a property known as "slenderness ratio."

Maximum practical height with no additional loads:  280 feet
Maximum allowable bending moment at tower top: 20,000 foot-pounds
Maximum vertical guy span under maximum loading conditions: 35 feet
Width of tower face between CG of legs:   22.59 inches
Projected area of one face per lineal foot of tower:  0.5513 sq. feet
Wind pressure per lineal foot of tower:   27.99 pounds (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)

Good luck,


---- Original message ----
>Date: Thu, 4 Oct 2007 14:10:31 -0400
>From: "jeremy-ca" <km1h at jeremy.mv.com>  
>Subject: [TowerTalk] AB-105 ratings  
>To: <towertalk at contesting.com>
>I have a chance to pick some new old surplus at a great price. How does it 
>compare to 45G as far as wind loading, torque and guy spacing?
>These appear to have been assembled in 60' sections with guy brackets and 
>never left the ground.

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