[TowerTalk] Base bolt depth in existing concrete

Hank Lonberg kr7x at comcast.net
Thu Aug 2 12:52:46 EDT 2007

Chris and others-

Google "Hilti" or "Powers Fasteners" you will find all the
information you need on epoxy adhesive bolts or anchors.

Epoxy bolts are the worst thing you can use in a situation
where there is vibration, cyclical or pure tension loading.
All Epoxy's creep over time with load and will quickly fail.
For these types of situations where you need to use post
installed anchors you need to use mechanical undercut styles
not epoxy. The above sites will discuss this in detail.

For a guyed tower base where the base is in compression and
shear, post-installed epoxy adhesive anchor rods are
perfectly fine.

Lonberg Design Group, Ltd.
H.S. Lonberg, P.E.,S.E.


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Chris
Sent: Thursday, August 02, 2007 7:04 AM
To: wb4slm at cox.net; towertalk at contesting.com
Subject: [TowerTalk] Base bolt depth in existing concrete

  Check out the epoxy's at Marine Tek. I've used them, and
they are very  good, especially for outdoor applications
with lots of moisture.
  As far as bolt depth, go as deep as you practically can.
When a bolt  pulls free from being embeded in concrete, it
can pull a cone of  concrete with it. Assuming bolt diameter
between 1/2 and 1",  I  would go a foot deep, because you
really don't know the tensile  strength of the concrete.
  Fortunately, for tower bases, the loads are usually more
shear than  tensile on the bolts.(Do NOT overtighten upon
assembly.) The location  of the holes, relative to the edges
of the "pad" also plays into the  equation. Err on the safe
side, and drill as deep as your patience or  drill bit will
allow, but I would make it at leat a foot deep in  "unknown"
concrete. Rent a BIG hammer drill, and wait for a cool day.
Keep the hole clean as you drill. Also,
  epoxy embedding can actually be better than direct casting
of the stud  in concrete when poured, especially in high
shear/vibration loads,  which can chip away at the high
stress points at the surface of the  concrete where the stud
enters. The epoxy can stabilize that interface.

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