The structural problem with monopoles is the effect of wind. Anything that adds
to the surface area exposed to wind, increases the wind load on the monopole and
As far as retrofitting monopoles, the biggest problem is with the foundation.
Most monopoles are made of pipe sections. The available pipe sections come in
discrete thicknesses. The minimum thickness for the original design loads
probably result in excess capacity that can be used by later additional loads.
However, the same excess capacity is rarely found in the monopole foundation.
These are usually designed using the "Pole Formula" found in the UBC. Embedment
depths are usually selected to the closest foot, with little excess capacity for
later additional loads.
If you absolutely must upgrade the capacity of a monopole foundation, you would
need access to a geotechnical investigation and a geotechnical engineer. The
geotechnical engineer can use the exact soil layer information with more precise
analytical methods to take out the conservatism often inherent in the UBC pole
Hope this helps.
Rick Drake, SE
Fluor Daniel, Aliso Viejo
JGPE1(--nospam--at)aol.com on 01/11/2000 07:50:15 PM
Please respond to seaint(--nospam--at)seaint.org
cc: (bcc: Rick Drake/AV/FD/FluorCorp)
Subject: Re: monopole antenae retrofit
I have a question about monopoles used for cellular antenna carriers. Has
anyone ever had to take an existing monoplole structure and camouflage it
with "branches" to make it look like a tree? Can such a retrofit be
accomplished when the existing monopole was originally designed without these
"branches"? A cell carrier has been asked by a municipality to do this if
they wish to increase the height of the existing monopole from 80 to 130 feet
however the cellular company has come back with "Structurally, it cannot be
accomplished". Is it a structural problem or more of an economical one? Is
anyone familiar with these monopole structures and can't they be modified to
support the additional loads? If so, how?
John G., PE