[TowerTalk] How much concrete to set a pole?
Frank N. Haas
kb4t at arrl.net
Mon Nov 7 13:57:50 EST 2005
Dear TTer's:
I am about to set 3 poles to secure elevated guys for my 40 foot Rohn 25
tower. I am trying to determine how much concrete to use (and how big/deep
a hole) to set the poles.
The 40 foot Rohn 25 tower was originally erected as a free standing tower
atop one (1) cubic yard of high strength Sakrete. After the first hurricane
blew through Florida in 2004 it became apparent that guying the tower is
necessary.
Due to the tower's placement on the lot and its proximity to the house,
elevated guys are required.
Three 21 foot long, 2.5" OD galvanized steel pipes are ready to go into the
ground approximately 22 feet from the tower. The limits of the lot force
this shorter than preferred distance.
The pipes have been drilled at 2 feet and 3.5 feet from the bottom to allow
four 1/2 inch x 2 foot rebar to be put through the pipe to minimize twist.
The current plan is the sink the pipes 5 feet deep into square holes dug 2
feet by 2 feet. The holes will be filled to the 4 foot level with High
Strength Sakrete mixed onsite. Dual eyebolts will be installed at the top
of each pipe to accept the guy wire from the tower and allow guying the
"back side" of the pipe to 2 earth anchors.
Each of the 3 pipes will be guyed to a pair of 5 foot long, 6 inch diameter
earth anchors 120 degrees offset from the guy wire that comes from the top
of the 40 foot tower. The earth anchors will only be 3 or 4 feet out from
the pole.
To fill the holes (2 x 2 x 5 feet) most concrete calculations dictate 30 80
lb bags of concrete. (2400 lb of concrete)
To fill the holes to the 4 foot level (2 x 2 x 4 feet) most concrete
calculations dictate 24 80 lb bags of concrete. (1920 lb of concrete)
A suggestion has been made to use only 15 bags of concrete (1200 lb) to
secure the base of the pipes.
Question 1: Given the size and type of pipe being used, what would be the
ideal dimensions of the hole (and thus the amount of concrete required)?
Are there any published guidelines for elevated tower guys? If so, where
can I find them?
The tower will not be heavily loaded. It is hope that a 3 element SteppIR
yagi and a single dual band VHF/UHF base station antenna will be installed
at the top. A pipe for a pulley to support the center of a 135 foot wire
antenna will also be installed at the top of the tower.
Any help appreciated. Thanks.
73,
Frank N. Haas KB4T
Florida
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