On 4/26/2014 10:00 PM, David Gilbert wrote:
I would agree with everything in that post except for the part about
drilling holes. I own an AN Wireless heavy duty 70 foot tower, and
every factory brace on it is held fastened to the legs with 5/16 inch
bolts/holes. In addition, when I purchased the tower I specifically
asked Dan (who was then the owner of AN Wireless) what the constraints
might be for drilling holes in the tower legs, and his answer was that
holes of the size normally used to receive bolts would not materially
weaken the legs at all. It's pretty much the same physics that allow
us to drill moderately sized holes in floor joints and roof trusses
without decreasing their load rating.
You have a tower that was designed to allow for drilling the legs for
braces, most tower are not and particularly towers constructed of
galvanized tubing.
These towers are designed to use a minimum of material and depend on
shape for strength.
Drilling holes on thin, galvanized tubing invites corrosion. Yours is
an exception. I would suggest that anyone who plans on drilling, or
welding to a tower leg, first contact the manufacturer before proceeding.
ROHN specifically tells users not to drill out bolt holes, let alone,
drill new ones.
Although I have solid copper ground wires cadwelded to the base
section buried in the concrete foundation, I was reluctant to risk the
annealing action that MIGHT occur on the tower legs above the
foundation, so the additional ground wires that I fastened to those
legs (I wanted to be able to demonstrate after the fact ... if needed
... that the tower was grounded)
As long as the ground wires do not leave the concrete below grade. That
is often specified in code and/or tower specs.
73
Roger (K8RI)
were done mechanically. I used half of a galvanized pipe ground clamp
and bolted it to the tower leg, attached the ground wire to the wire
lug, and then spray painted the entire connection with galvanizing
spray. No hassles, no worries.
73,
Dave AB7E
On 4/26/2014 2:05 PM, Roger (K8RI) on TT wrote:
On 4/26/2014 1:00 PM, Warren Wolff via TowerTalk wrote:
My Tower guy wants to CadWeld my copper to the
legs of my AN Wireless tower. This worries me.
I'd pass on CadWelding directly to tower legs. CadWelding melts a
goof portion of the base metal and alloys it with the copper and the
Aluminum in the CadWeldinf material. It makes a very good electrical
joint, but would severely weeked the portion to the legs that is
melted. It also heats quie ab=n area areound the weld to red hot,
which slowly cools.
I don't know the temper of the legs, but any present temper is likely
reduced. I would neither heat the legs to a temper reducing dull
red, or hotter, nor would I allow holes to be drilled the the legs
and particularly no holes in galvanizing. ROHN specifically warns
against drilling out tight fitting bolt holes, or using the bolt to
thread its way in. To enlarge the holes, use a long taper pin with a
gradual taper. This will open the hole enough to allow "sliding" the
bolt in and leaves the galvanizing in tact! You may have to drive the
taper pin in from both directions.
As a general rule, for tower legs, don't heat, don't weld, and don't
drill.
73
Roger (K8RI)
Warren
W7WY
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