[TowerTalk] Adjustments to Tower Base Pier J-Bolts
w9ac at arrl.net
Sat Jul 22 20:06:23 EDT 2017
>"In the future, people using long rods should consider two templates with
one at the normal location and a second at the top of the bolts.":
Amen. After seeing the problem on the day after the pour, you could hear me
swearing at Pirod Engineering for not specifying two (2) templates: One just
above the concreate surface, and the other at the top of the J-bolts. Done
that way, it would be next to impossible to have a problem because the
entire 12-inches of exposed bolts above the concrete surface would stay
perfectly vertical. Double-nutting as specified by Pirod is not nearly good
enough to ensure that the bolts stay vertical during the pour. There can be
a tremendous amount of pressure applied to the bolts during the pour -- as I
found out the hard way.
Several folks want to know why there's 12" of exposed bolt above the
surface. That's Pirod's design spec., but also keep in mind that a
self-supporting tower base foot does not rest on concrete. It actually
rests on a nut as a leveling device. The nut under the foot is adjusted to
level a self-supporting tower. So, here's the actual length needed:
First, the nuts are all 2" in height and the bottom nut is spun to 1.5"
above the concrete surface -- again to allow for leveling. Next, add a high
strength flat washer, lock washer, followed by the height of the tower foot
which is 3.0". We then add more hardware and another nut to the top. All
the washers together are 0.5" in height. So we end up with:
1.5+0.25+2.0+0.25+3.0+0.25+2.0 = 9.0 inches, leaving 3 inches at the top.
Probably the most I'd ever cut is maybe 1 inch off the top and that means
cutting 1 inch off of four extra-high-strength steel bolts is almost
certainly not worth the effort.
I've received many interesting replies and will consider all of them.
Several folks seem to think my issue is just getting the template off.
That's the least of my trouble. I can cut it off tomorrow. I need to know
that it can come off *intact* so that the tower base will go on without
friction. Slight reaming of the tower base holes is also an option but
grinding four, 3-inch thick holes will be one helluva' job.
One common theme, especially coming from the registered PEs in the group is
to avoid any heating of the J-bolts due to weakening and burning of the
galvanized surface. So, that's out of the question.
Although not related, my second lesson relates to the blowing out of the
concrete form during the pour. Recall that the base pier is a 10 Ft. cube
and takes a LOT of concrete. Long story short: Use a separate frame about
6" in height, made from 2"x6" lumber, just above the earth surface. The
upper frame lays on top of the larger 10 cu. Ft. frame below the earth
surface. Hell, let the bottom frame blow out during the pour. Who cares as
long as the upper frame that shows above the earth surface remains perfectly
square. It's unfortunate, but I would have never learned this any other way
than to learn these mistakes once.
I'll provide an epilogue after the final fix. Many thanks for all the
The "lots of grease and use the bottom nuts to force the template up"
MIGHT work, but it might bugger up the threads.
73, Roger (K8RI)
On 7/22/2017 Saturday 11:49 AM, K7LXC--- via TowerTalk wrote:
>> Got a nasty situation here that needs some brain power to resolve.
> this year, I poured two base piers for a pair of Pirod self-supporting
> towers. The 140 ft. tower base has the problem. Unfortunately, the
> J-bolts on two of the three equilateral triangle points are bent
> inward, toward the base center by 1/8". That 1/8" may not seem like
> much, but it is. In fact, the template used during the pour cannot
> be removed. During the pour, the J-bolts were double-nutted, one on
> top and the other below the template. Still, the force of the
> concrete pour managed to push out the 6 ft. J-bolts. As that was
> settling, I quickly moved the crew to the other tower as sunset was
> minutes away. I did not go back and take a level to the bolts,
> thinking the template would keep them perfectly straight.
>> Each 6 ft. bolt is exactly 1-7/8" in diameter. Each protrudes 12"
> above the
> concrete surface. Moving these huge bolts even 1/8" will take a
> Herculean effort. The template holes are the exact same diameter and
> made that way to minimize shift of the type that occurred anyway.
> The tower base section has mounting holes that are exactly 2.0" in
> diameter. So, there's just a small amount of wiggle room. If we can
> get the template off, then I know that the tower base will absolutely
> go on without trouble.
>> Some options:
> 1) Use an oxy-acetylene torch and apply heat at the point where the
> J-bolts exit the base, then pound with a sledge hammer. Trying it
> now without heat is futile; we've tried and the bolts are going
> nowhere. I have no idea what heating will do to the strength of the
> 2) Use a telescoping hydraulic cylinder (a.k.a. hydraulic ram jack) to
> the two J-bolts against each other since they are both leaning in by
> the same amount. What I don't know is how much adjusting precision
> I'll have when expanding the cylinder. Do these things move in very
> small increments?
> What cannot occur is the cylinder "jerking" the bolts to anything
> beyond 1/8". These cylinders are capable of pushing 30,000 lbs. and
> are typically used on large earth-moving front loaders
> Heating the bolts should be okay. I don't think it'll
> appreciably cause a problem - but I'm not an engineer, just a tower
> builder. Use a 6' or so piece of pipe as a lever to help move them.
> The other thing you could do would be to enlarge the leg holes
> to accommodate the slight off-set. That'd be what I'd do.
> Cheers & GL,
> Steve K7LXC
> TOWER TECH -
> Professional tower services for amateurs
> TowerTalk mailing list
> TowerTalk at contesting.com
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