[TowerTalk] tower replacement wisdom

[Jeff DePolo]

> I have the following limitations:
> 1. I want to have minimal downtime - the tower has a couple 
> of heavily-used
> ham repeaters, a commercial repeater, and a wireless ISP on it.

Lacking any historical design data or details on what you have in the
ground, don't plan on re-using any foundations or anchors without testing.
Even with testing, it is doubtful that your AHJ would issue a permit that
allows for re-use of a foundation.  After all, you're going in telling them
that the structure needs to be replaced due to its age, being beyond its
service life, etc..  Any half-competent building inspector is going to
consider the foundations, anchors, guy wires, etc. part of the structure,
not just the vertical steel.

> 2. The county would never issue a permit for a tower like 
> this today... the
> property has a use permit for the tower, specified as "18 
> inch face" and a
> drawing of its approximate location on the property. 

This should be an easy issue to get around.  EIA/TIA-222 has been revised 5
or 6 times since that tower was built.  You didn't give too much detail on
the loads (including cables which are often a bigger load than the antenna
itself), but it's quite likely that your existing tower would not pass under
recent 222 revisions (do you know what rev your local building codes
require?).  Assuming you are entitled to a functionally-equivalent
replacement, the AHJ can't force you to build a structure that you can
demonstrate does not meet current codes and would not be safe.

> 3. I have no construction drawings for the guy anchors or the 
> tower base, and have no way of nondestructively testing the strength of 
> the guy anchor rods.

See #1 above.

> 4. I'd like to ensure that the tower can support the existing 
> and future
> microwave dish loads, and reduce the twist both for those and the fire
> detection cameras I have up top... so maybe should go to star guying?

Depends on what kind of tower you end up with, what the requirements are for
the microwave paths as far as twist and sway, etc..  Do the math and
engineering, then design/select the tower.

Most AHJ's tolerate, if not encourage, building new or replacement towers
with loading capacity beyond what is needed for the initial intended purpose
as it potentially means one (or more) additional towers would NOT need to be
built in that area to handle future tenants/loads.  Around here, it is
typical for zoning regulations to include such language as a requirement for
commercial towers.  Whether or not that applies to your "hobby" tower and
whatever non-commercial limitations are put on it as far as zoning or use, I
don't know.

					--- Jeff WN3A


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