Date: Sun, 15 Apr 2012 22:19:35 -0700
From: "Mike Baker" <k7dd@cox.net>
Subject: Re: [TowerTalk] Anchor bolts for LM470
It is not necessary to coat the anchor bolts with anything.
When the steel is encased in concrete it cuts of the supply of Oxygen so it
doesn't rust. If steel rusted inside concrete you would have to galvanize
rebar.
Use of an extension type concrete vibrator while doing the pour will spread
it out and settle any air pockets out of it. If you just place the vibrator
on the side or top of the bolt when installed for a few seconds it will
settle the mix around the bolt quite nicely and keep out the air pockets.
That is a worse case scenario.
Mike Baker K7DD
"My thoughts!":
The bolt head, J, flag, or plate only needs to be big enough to prevent the
anchor from turning, pulling out, or over stressing that small area of
concrete. I think J-bolts are by far the cheapest and easiest to make if
you do-it-yourself.
As for "All Thread" which is plain old threaded rod, isn't it a bit soft to
use? I've never seen it except in ungraded strength. I've been planning on
using 1" or 1.25" bolts, 3 feet (give or take and boy are they heavy!) long
with a 1/4" X 6 X 6 or even 4 X 4 flat plate welded on the bottom and a
couple of 1/4" thick ears welded on the sides at the base for my projects.
The thing about hard bolts is they rust more easily so they have to be
protected. You can also tape the threaded portion that goes through the
base. I'll be using a separate base so the plans call for the bolts to be
installed in the base which will then be lowered over the hole. The base
needs to be leveled and secure before the concrete is poured and care used
to completely encase the bolt heads in concrete with no voids. Protect the
threads to allow for re leveling the base and removing the base after the
concrete has cured. Use Tape, Saran Wrap(TM) or what ever comes to mind.
Then warm them up to about 50C and liberally coat them with thinned tar. If
necessary recoat with tar about twice as thick as the original coat. If the
bolts are clean, dry, and fairly warm (or hot) the tar will uniformly adhere
and not come off. it stinks but it works. Also you can get the nuts off if
you ever need to. Just don't heat them enough to take the temper out which
is really hot.
Undoubtedly there are others on here who have alternate methods of
protecting the base hold down bolts.
73
Roger (K8RI)
>
## Roger + Mike. You folks are making a mountain out of a mole hill.
I bought 12 x anchor rods, each 1.125” x 5’ long from Portland Bolt,
in Portland Ore. They are heavily galvanized, and I had em made with
6 inchs of thread on each end. They are 105 ksi yield strength. You
can get anchor bolts in 36 ksi, 55 ksi and 105 ksi. They colour code
one end of em in blue-yellow-red. (36-55-105).
http://www.f1554anchorbolts.com/
## J bolts are now out of vogue..and are not allowed in most places. L bolts,
and C bolts are the new standard. Buying anchor bolts that have not been
heavily
galvanized is plane nuts. You then order the mating heavy duty matching
galvanized nuts,
plus heavy duty galvanized flat washers. Normal nuts are exactly 50% wider
than the bolt material.
The heavy duty versions are slightly bigger than this. Portland Bolt will
make anchor rods as long as
you want..like 20 feet long if you want. They can also make em up to 4 inch
diam. You can also get
em with cut threads or rolled threads. Normal washers have an oversized hole
in the middle, and
a huge OD. The heavy duty, HARDENED variety have holes that just fit the
rod, and slightly smaller
OD. There is a big diff between TQ and tightness. The threaded portions
have to be slopped with marine
grade never seize..like the type made by locktite.
## On the base for my HDX-689, the anchor rods are placed in 3 groups of 4.
A 9 inch square plate,
.375” thick is placed on the bottom of each group of 4 x rods, with 4 nuts on
each side, and cranked down
real tight with an impact wrench. That alone will increase the uplift
capacity by several hundred %.
## The anchor rod depth into the concrete should be one half of the depth of
the hole. My hole is
9 feet deep, so 4.5 ft into the cement..leaving 6 inchs of thread above the
concrete. That’s why I had em
cut 6 Inch threads on each end of all 12 rods..then its galvanized. Junk like
J bolts and washers welded to the ends of the rods
won’t get past city hall engineers here in a million years. By using a 9 inch
square plate ....which is galvanized,
on each group of 4 rods, the rods can not rotate on their axis, nor can the
pull out.
## BTW, rebar WILL rust inside concrete, it happens all the time. That’s why
the rebar cage cant sit on the dirt
at the bottom of the hole, it has to sit on small concrete dobe blocks. More
and more rebar is also being painted.
Use 60 ksi weldable re-bar and not the 40 ksi Un weldable crap. We have a
condo here in town that got water up from
below, and the rebar inside the concrete has vanished, eaten itself in way too
many places. The entire building is
starting to lean like the tower of pizza.
## roger , the all threaded rod you are thinking of, that is real weak is
called ready rod. That’s hardware store junk,
not anchor bolt material.
## UST on its diagram for the 689 tower,sez to use 36 inch long bolts with 6
inchs above the concrete. And 36 ksi
bolts to be used. There is no pint in having a 30 inchs of rod embedded in a
9 ft deep block of cement. UST’s new standard
of 55 ksi rods, but only 27 inch long is even worse. The ONLY thing that’s
holding the 5600 lb tower tot the 17 cubic yard
base is the 12 x anchor rods. 36 ksi rods with hardly and embedment depth is
fubar, and just asking for trbl.
## Building codes have changed several times over the last 20 years. J bolts
are history for the most part. Any anchor rod
not galvanized is history. 36 ksi is no longer acceptable, only 55 and 105
ksi rods. 3000 psi concrete doesn’t cut it anymore either.
4350-5075 psi range is more the norm. So forget the saran wrap and tar,
etc..and just engineer it right the 1st time. Take a close
look at the 100ft tall mono tubes used at cell sites and also used for
lighting at sports venues,and see how they do it. 2 inch
bolts, 4 inch nuts. Galvanized split ring lock washers are passe too. You
wont see their use on anchor bolts anywhere.
## Concrete vibrators HAVE to be used, esp in the area immediately below the
flat plates used on the bottoms of the anchor bolts.
rent one with a 15 ft hose on it. You can also hold em right up against the
cage itself..and vibrate the daylights out of the cage.
You only want to vibrate just enough to do the job and no more. Otherwise
your aggregate will sink. If using a line pump for the
cement, aggregate cant be bigger than ,375 inch.
later... Jim VE7RF
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