On 3/25/18 11:41 AM, Fred Keen via TowerTalk wrote:
Methinks there is a mixture here of 'quickbolts' and 'anchor in when concrete
is poured bolts'.
Chemical anchors (the industry term for glued in bolts) and "poured/cast
in place" anchors are about the same strength. Some engineers actually
prefer the chemical anchor - the adhesive engages the threads since it's
more fluid and less viscous, so there's more "contact area" between the
body of the concrete and the bolt itself.
They also like it because you don't have to have as tight a tolerance on
the concrete work lateral position. If the concrete's a bit off in
position, it doesn't matter, because you lay the template (or the actual
base) down and use it to guide where the holes get drilled.
You also don't have to worry about the bolts moving (or getting out of
plumb) while you're pouring the concrete.
Of course, it costs more - the adhesive costs something, the drilling
costs something, and you DO have to make sure your drilling is straight
and plumb.
If you're inheriting a legacy design from 1950 (when reliable cheap
adhesives didn't exist), or you're concerned about reducing cost to the
absolute minimum, cast in place bolts are what you'd use. Or, if there's
some peculiarity of the location - maybe you're pouring the concrete
under water. (although I'll bet the chemical anchor folks have a
solution for that, too)
On Sunday, March 25, 2018, 1:11:19 PM CDT, Jim Thomson
<jim.thom@telus.net> wrote:
Date: Sat, 24 Mar 2018 11:51:44 -0700
From: "Steve Jones" <n6sj@earthlink.net>
To: "'Hans Hammarquist'" <hanslg@aol.com>
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Achor bolts?
Message-ID: <002701d3c3a1$27fd50a0$77f7f1e0$@earthlink.net>
Content-Type: text/plain; charset="us-ascii"
<My 89' US Tower crankup has 2 anchor bolts at each leg, a total of 6 bolts.
<Each bolt is 1 -1/8" diameter and 27" long of ASTM grade 36 steel.
<I think I'd trust US Tower's licensed PE wet-stamped drawing before
<Facebook!
<73,
<Steve
<N6SJ
## I have the 5000 lb, old style UST HDX-689 89’ tall tower. It uses 12 x anchor
bolts, 4 per corner.
Each group of 4 x rods are in a square config, aprx 5.25 inches C to C.
Each anchor rod is 1.125 inch diam x 60 inches long. Each rod has a 6 inch
thread on each end. Anchor rods
come in 3 x different astm strengths.... and each top is color coded. The 36 ksi are
blue. The 57 ksi are green,
and the 103 ksi are red. I used the red / 103 ksi versions. You require a full 6
inches of threaded rod sticking
out of the concrete for the mating 640 lb steel base..which is 1 inch thick.
The new version of the same 89 ft
tower uses W bracing, weighs less, at only 3250 lbs, but uses even bigger diam
anchors.... 1.25 inch diameter.
## UST specified 36 ksi rods that are only 36 inches long.... which leaves
only 30 inches embedded in the concrete.
The finished concrete top can be any where from flush to the lawn, to a max
of 8 inches above the lawn. If the finished
concrete is 8 inches above the lawn, the bottoms of each anchor rod are only
22 inches below the lawn.
## My base is 6.9 ft x 6.9 ft x 9 ft deep. Aprx 5.5 inches above the lawn, 17
yards in total.
5075 psi concrete used. Seems silly to me to have a base thats 9 ft deep, with anchor
rods that are only 22-30 in below
lawn level. So I had portland bolt custom make the anchor rods longer, 60
inches, and also had em turn a 6 inch thread on
each end of each rod. Then had them use the 103 ksi material. Then had the
local metal shop fabricate 3 x identical plates for me.
Each plate is 9 inches square by .375 inches thick, with 4 x holes punched
out. One plate at the bottom of each 4 x rod assy.
1 13/16 wrench + deep impact socket used to tighten the 8 x nuts that hold each plate
in place. The 9x9 plate increases the
pull out capacity through the roof, compared to using either nothing, or
perhaps a stack of washers.
## Per the engineers I talked to, if the rods are not embedded deep enough, and the
base lets go, you end up with whats called...
base blow out. Looks like a real shallow angled funnel, no deeper than the
embedded rod depth and aprx the same dimensions
as the top of the finished concrete.
## I also re-designed the rebar cage, used 50 % more vert rebars, 9 inches
inside to inside, around the perimeter. 24 x 1 inch rebars in total.
A lot more 15mm one piece horizontals used, since there is a horizontal for every 6 inchs
of embedded anchor rod, then its every 12 inches after that.
Also installed a horizontal grid of re-bars, one just below the lawn level..and a 2nd
grid, just below the three 9 x 9 plates.
## UST towers are not ICE rated, nor is the tower, nor the oem UST base, seismic
rated. Being in a residential area, typ postage stamp sized lot, 87 x 115, the concrete
base install is a one shot deal. You dont get a 2nd chance to do it right. With
the .375 thick chromolly mast on top, + ants, prop pitch, cabling, 2 x bearing plates,
mast steps,
etc, etc, the total weight is aprx 5500 lbs. The ONLY thing connecting the 5500 lb tower to
the 70,000 lb concrete base is the anchor rods !! And some idiot on face book
wants to use $3.00 home depot anchor rods, wtf? Anchor rods are the LAST
place you want to cut corners.....and...save money.
## IF you are on acreage, and the tower falls over..and knocks over a few
bails of hay, go for it.
Later.... Jim VE7RF
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