The rebar cage for my "shipping real soon now" tower came ahead of time
as I requested. It is mostly 1 1/4 inch (#10) rebar but has some cross
braces of 1/2 inch (#4.) I was offered my choice of two patterns, one
to be used with a 5 ft diameter hole 8 ft deep and the other (the one I
selected) is for a 4x4x8 ft hole. I got two bids on the 5 ft x 8 ft
round hole and both were over $1000 so I went for the rectangular hole
which has been quoted from $200 up and by one guy at $80/hr.
There is rebar made to be welded and then there is the common rebar
readily available at all the big box stores. The common rebar can be
welded but the results can be catastrophic when least expected.
I noted the 2 inch cover and that really caught my eye. Once upon a time
a long time ago I was told to have a minimum cover of 2 inches but
subsequent to that I think the recommended cover has been increased.
The Rohn documentation may be vintage material not updated to modern
thinking.
A quick Google and the first few hits had this to say: principal
structural members in which the concrete is deposited directly against
the ground, cover to the bottom reinforcement shall be 75 mm.
ACI 318-05 7.7.1:
Concrete cast against earth - 3" cover minimum,
*Minimum**Concrete**Cover*:*Concrete *cast against and permanently
exposed to earth: 3"
So there you have it: I would go at least 3 inches. More cover doesn't
violate Rohn specs it exceeds them which is OK.
Patrick NJ5G
On 10/20/2015 10:29 AM, StellarCAT wrote:
Rohn says to use 8 #7 rebar (SERIOUSLY! 7/8”!!) ... and then it shows ‘#4 circular ties 2 1/2” OC
with 2” cover with 24” laps’
huh?
I’ve always just dug a hole – usually around 3 x 3 x 3 ... put the tower section in (with temp guys) ... put in a
few pieces of 1/2” re bar and been done with it .... but now I have to follow the Rohn specifications which seem onerous
at best (I know, I know – guys that say “follow it to the letter”) ... and I’ve no clue what #4
circular tie is. SURELY its not #4 rebar BENT in a circle!?
Googling so far hasn’t shown me anything that helps.
Gary
K9RX
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