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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