Tnx Mike. I have doubts if an epoxy bond will develop enough strength to hold a
large bolt to its tensile breaking strength. Would like to see some test data on
this. The strength of a bolt goes up as the square of its diameter (cross
sectional area) but the epoxy bonds to the surface which increases only
proportional to its diameter. As the bolts become larger and larger in diameter,
the epoxy bond faces increasing difficulty in holding it to its ultimate
breaking strength. In construction, I believe, bolts are seldom stressed
anywhere near their ultimate strength.
Zak, Mike wrote:
> I like your idea best.
>
> 73, Mike - K1MZ
>
> Mike Zak
>
> -----Original Message-----
> From: dan hearn [SMTP:dhearn@ix.netcom.com]
> Sent: Sunday, March 21, 1999 8:35 PM
> To: Jepilot@aol.com
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Rplacement stud bolt
>
> The original bolts in the base, of course have a J hook which is
> very secure in
> the cement. It seems that any straight bolt would be weaker though
> that is a guess
> on my part. If I had that problem, I would take the T base to a good
> welder and
> have him weld a short piece of rectangular bar to it with a hole in
> the proper
> place. The factory T bar for my TX472 is fabricated with a weld in
> it anyhow. The
> nuts on the present studs allow for any vertical misalignment and
> you can add some
> washers if needed. If the present stud is far enough out of
> alignment with the
> tower leg to worry you, the welder could even weld a small piece of
> vertically
> aligned bar to prevent twisting. 73, Dan, N5AR
>
> Jepilot@aol.com wrote:
>
> > Problem: How to install a stud bolt in an existing concrete base.
> >
> > Background: WD5FHG and I are in the process of
> installing/erecting a new 55
> > foot crankup, self supporting tower (US Tower, HDX555). This
> tower is
> > replacing an earlier HDX555 which was destroyed when the cable
> broke on the
> > fully extended tower. What a mess.
> >
> > The new HDX555 tower has the same type of base as the previous
> tower. Three
> > stud bolts are installed in the massive concrete base, a steel T
> frame base is
> > bolted to the three stud bolts, two legs of the tower are bolted
> to the base
> > frame, and the tower is pulled up with an erection fixture to the
> vertical
> > position. I imagine a few hundred readers have been through this
> process.
> >
> > However the problem arises because one of the mounting holes in
> the steel
> > frame does not match up with the stud bolt in the concrete base.
> The holes at
> > each end of the top of the T match perfectly but the hole for the
> bolt at the
> > bottom of the T is not even close. So we propse to install a new
> bolt in the
> > existing concrete base.
> >
> > Proposed Solution: We propose to have an all thread bolt
> fabricated by a
> > local machine shop using high quality steel (same specs used for
> the factory
> > furnished studs). The stud would be 1-1/8 inch diameter and about
> 18 inches
> > long, threaded its entire length. A 1-1/2 inch diameter hole
> would be
> > drilled in the concrete base about 12 inches deep which will allow
> the stud to
> > extend about 6 inches above the top of the concrete. The stud is
> to be
> > threaded it's entire length to allow a better grip for the epoxy
> > adhesive.Obviously there is 3/16 of an inch between the wall of
> the hole
> > drilled in the base and the stud.
> >
> > Issues: What is available to hold the stud in place? In the old
> days, hot,
> > liquid sulphur was used for this purpose, which when cooled held
> the stud
> > very well. I suppose there is now available some type of epoxy
> for this
> > purpose. Any thoughts on this?
> >
> > Is 12 inches deep enough for this application? The concern is, of
> course,
> > failure of the epoxy and/or this method of installation while the
> bolt is in
> > tension, allowing the bolt to be pulled out of the base.
> >
> > Is a 3/16 annulus too little, too much, just right, to allow
> adequate space
> > for the epoxy to bind the bolt threads to the side wall of the
> hole?
> >
> > Any other thoughts? Thanks for your comments, advice and
> suggestions.
> >
> > Jan Rehler, W5KNZ, Corpus Christi, Texas
> >
> > --
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