Don,
"proper" is a poor choice of words. Towers can be engineered either
way, and there are pros and cons for each approach. How the tower is
loaded with antennas sometimes affects the base choice as well. As long
as the design is within the allowable limits for the tower sections,
there is no reason to expect the failures you cite. You should know
that there aren't "hole in the base plate" pier pin bases made for 65
and that Rohn supplies buried bases for 25, 45, 55, and 65 at a fraction
of the cost of pier pin solutions.
From what I've seen and heard about tower failures, guyed towers almost
always come down when a guy fails in some manner (turnbuckle, insulator,
termination, guy corrosion, tree fall, vehicle contact, etc etc), not
sheared bolts or fatigue failures.
I'm confident the PE did a great job for my buried base 65 tower, it is
a trivial structure compared to his day job. It was erected and plumbed
in about 5 hours, 142' and there wasn't a tapered section in the prior
install.
see http://www.publicsurplus.com/sms/auction/view?auc=1537335 for a
commercial 160' tower for sale, not pier pin.
Grant KZ1W
On 2/8/2016 11:19 AM, Donald Chester wrote:
I can't understand why so many hams build towers this way, especially a former
AM BCB tower. The proper way to erect a guyed tower, particularly one more than
about
50' tall, is to attach a flat base plate to the bottom of the tower. The base plate has
a hole at the centre of the triangle formed by the tower legs. A galvanised steel pier
pin is embedded in the concrete base pier, and extends up 4" to 6" above the
surface of the concrete. The first tower section is merely set on top of the concrete,
with the pier pin sticking up through the hole, held vertical with a set of temporary
guys that remain in place until the first permanent set of guys is attached That way,
the tower is free to rock and sway back and forth on the concrete, and maybe even rotate,
in heavy wind gusts. This puts far less stress on the structure of tower sections. With
a rigidly attached bottom section buried in the concrete, any motion caused by winds
causes bending and twisting of the tower structure. This unnecessary stress can
eventually cause weld failures and even shear bolts.
Another plus, the base plate alleviates the necessity to absolutely perfectly
plumb the bottom section before stacking the rest of the tower. After the job
is finished, the tower can be fine-plumbed by adjusting the guy wires, without
permanently stressing the tower.
Temporarily guying the bottom section and plumbing it to the best of one's
ability before stacking the rest of the tower sections is certainly easier and
less critical that trying to get the bottom section PERFECTLY plumb in the
concrete (temporary guys still required) before proceeding.
With a substantial communications or broadcast tower, the bottom section was
probably tapered to a point to begin with, making it unnecessary to even
purchase or construct a base plate, and the pointed end allows even more
freedom of movement with winds and guy wire adjustments.
How many large commercial towers have you even seen with the bottom section
buried in concrete?
Don k4kyv
Mon Feb 1 10:54:50 EST 2016
Grant Saviers grants2 at pacbell.net wrote:
Interesting. My R65 is 15+ years old, former AM BCB
tower, 20 foot
sections.
Grant KZ1W
On 1/30/2016 19:46 PM, john at kk9a.com wrote:
There are no weep holes in my Rohn 65G.
John KK9A
To: Dan Cisson<n4gnr at windstream.net>, 'Patrick Greenlee'
<patrick_g at windstream.net>,towertalk at contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: Tower buried section legs --
Buried in Concrete orBelow the Concrete?
From: Grant Saviers<grants2 at pacbell.net>
Date: Fri, 29 Jan 2016 11:12:06 -0800
FYI, Rohn 65 with 4 bolt 5/8" thick flanges on each leg has one 1/4" weep
hole on each leg, at both ends right next to the flange. The flanges are
drilled to the leg od and welded outside and inside to the tube before
galvanizing. So there are redundant paths for water to escape. My PE
specified 1 foot of 3/4 gravel for the legs to be set into before the 4x4x2'
base pad was poured.
Grant KZ1W
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|