Tower project - Phase 2 Complete
 

Dear Marv W5MTV:

Your antenna system is complex enough that you should have it analyzed by a
professional engineer who has experience with TIA 222G standard.
Understanding of what constitutes safe tower practice has evolved a great
deal over the past many years. An early version of 222 was much shorter
than the current 222G standard. Unfortunately, some antenna and tower
manufacturers are still using earlier standards.

Not to have the system evaluated could cause big problems if something
fails.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"MTV" wrote in message
...
For what it's worth - may be interesting to those contemplating a similar
project:

Phase 1 was finding 'such a deal' on a full sized 7-element Mosley Pro
57-B five band beam. Also researching towers that I wouldn't have to climb
and still reach above my trees of 30-45'. e.g. 50' tower.

My first choice was a Heights crank-up, but cost moved me to Glen Martin
Engineering's M-1350A package deal. (13" wide legs; 50' high w/guys) and
their "Hazer" system to raise and lower the beam (with one or two guys
temporarily disconnected at the ground).

Phase 2 was first digging the 36' x 36" x 45" hole for the base, then
securing the tower rod base and pouring the concrete.

It took almost two weeks of occasional digging with a handy small
"striker" shovel to dig the hole. That shovel holds just what I can lift
up to the wheel barrow, and is easy to maneuver in the hole. I used a wood
2 x 4 frame which is also used for the top of the concrete platform. Easy
then to keep sides vertical in line with the frame. The soil is a firm
clayish-dirt mix. A problem not explained is what to use in the hole to
support the metal tower rod base which only goes 28" into the hole. Why
don't the manufacturers just make available longer rod supports? I ended
up using concrete blocks under each of the 3 tower rods with a couple
bricks on top to just equal the requirement for the rods with nuts to
extend above the concrete the proper length. One handbook suggested a
rebar wire cage in the hole, but I had no way to bend or weld rebar. I did
try, driving around one morning to various shops with welding equipment,
but none could or would do it. So, I cut various lengths of rebar and
wired them at various angles and levels to the base and through the cinder
blocks without going into the dirt sides. It made lots of surface area for
concrete adherence.

The concrete: I'd checked some local concrete companies and had only two
that responded with any interest. Actually, the closest to my home quoted
me a price of $426 when I stopped by and asked, including a $125 delivery
charge. Yikes! And it was close by and my "hole" was accessible so the
truck could back right up and dump the load. As it turned out, when I was
ready for the delivery I stopped by to prepay, and they lowered their
price to $195 for 1.5 cu. yds., 3000+ spec, and no charge for delivery.
I'd expected delivery in a few days, but they said they'd be over in about
15 minutes. They were, made the delivery, cleaned up their chutes, and in
another 30 minutes I had it all smoothed out and finished!

I'll be letting it dry for at least a week. Now I'll be on to Phase 3,
driving guy anchors into the ground, assembling the tower pieces, and
preparing for the "several guys" walking up the tower into the air with
the hinge mount in the base secure.

To be continued

Marv W5MTV

Tower project - Phase 2 Complete
 

Jim Lux wrote:
MTV wrote:
Jim Lux wrote:
MTV wrote:
Allodoxaphobia wrote:
On Sat, 07 Mar 2009 15:03:33 -0600, MTV wrote:

Thanks Jim,

Since I'm in far NW Harris County I'm in the "35 psf" zone, whatever
that is. Right on the coast is "45 psf."

Yes, we have hurricane straps.

As far as the max wind speed I trust the actual we had w. Hurr. Ike and
Rita. When Ike came back from the north, we were on dead on the eye of
the storm and locally measured 87 mph at IAH. It was 'winding down' at
that time, but still toppled huge trees all around. Just lost one on our
property, but just missed demolitioning one home. Of course, it was one
of those "100 year storms" that we've had three of now in 20 yrs.

The max vertical weight on the tower per leg is 8750 lbs so I doubt one
more guy would matter. Good advice on not using house bracket. My
thought was that it would be a safety factor when guys would be down
when raising the antenna. Of course, I wouldn't do anything with a
strong wind blowing.

I have two engineer son-in-laws that should be able to calculate per
modern stds.

Marv


most residential roof construction is mostly designed to use gravity to
keep the roof on and to support down forces. They don't resist upforce
well (unless you're in an area where the code encourages straps..
hurricane areas, for instance), nor do they resist side loads. The house
itself can usually take a fairly good side load (after all, there's all
that surface area exposed to the wind), but the fascia boards on the
roof can't, so you have a problem of transferring the loads from the
antenna/guy to the structure of the house.

Different areas of the country have different construction practices to
accommodate the loads that are important (e.g. my house in southern
California is designed to resist shaking loads in shear from
earthquakes, but I doubt the roof could take many feet of wet snow)


Watch out with 4 guys rather than 3.. The limiting thing on a guyed
tower is the downforce on the tower under load. If you have 4 guys, you
have more static load on the tower than with 3 (assuming you've
tensioned them the same), so you're that much closer to the failure
point. Glen Martin doesn't have a whole lot of useful engineering data
on their web site, so it's hard to even do a back of the envelope
calculation of the buckling loads on the vertical tubes.

And you gotta love the picture of a bunch of guys standing underneath
the tower they're tilting up without any sort of safety precautions.

Marv