Towers and ice.

Tue, 20 Aug 96 10:53:22 cst

Ice adds wind area and weight to a tower. Towers with smaller members are 
more affected than towers with larger members from a percentage stand 
point. Ice is generally not good for the health of any tower.

                w/o ice         w/ 1/2" radial ice
Rohn 25
+ 3/4 hardline on each face

Effective Area  1.61            3.70    ft^2/section
Weight          41.20           97.44   lb. / section

Rohn 55
+ 3/4 hardline on each face

Effective Area  2.10            4.40    ft^2/section
Weight          95.0            192.40  lb. / section

Other than the weight of the tower section, 45 looks like 55.

These are per EIA-222 Rev E. from some calcs I did for a guy trying to make a 
choice. The standard specifies that the wind pressure can be reduced to 75% of 
the normal wind pressure. 

Some local meterological data may indicate that a lower percentage may be 
applicable in your area. Check with your state climatologist or meterological 

I usually use 25 pounds per square foot to keep the math simple and most towers 
I deal with for amateurs are in an 80 MPH wind district and under a 100 ft so it
gives me a good ball park number when asked for an informal opinion.

Anyway the ice load on Rohn 25 increases the wind area by (3.70/1.61) = 2.29.

I generally find ice loading to be the most severe case when evaluating a tower.

Of course if you live in Florida, then ice is not much of a concern, just 

de n0yvy steve

______________________________ Reply Separator _________________________________
Subject: Towers and ice.
Author:  Gene Smith <> at ccmgw1
Date:    8/19/96 2:39 PM

I have been trying to determine the effect of ice on a tower such as Rohn 25G.  
Rohn gives antenna wind loading sizes with and 
without ice for their freestanding 25G but not for 
bracketed or guyed.

I emailed Rohn about obtaining the max antenna 
size with ice for their 25G and 45G towers for 
a bracketed installation.

The next day I received a phone call from a 
gentleman from Rohn explaining that ice is not 
really a problem with high wind speed because 
the wind blows the ice off the tower.  He went 
on to say that Rohn installed a tower in
my area (Cleveland/Medina, OH) for a utility 
company and that they used the non-ice wind loading
numbers for the installation.  He said that the 
reason the ice numbers do exist in the 
documentation for the freestanding tower 
versions is because marketing wanted it.

Is this really true?  What are the real 
effects of ice on a tower?