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Re: Radiographic inspection

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In my experience, we have used a pachometer to locate all of the reinforcing
in the area of the proposed hole.  The reinforcing found by the pachometer
is compared to the approximate location of the pt cables.  My first step
would be to move the hole away from any reinforcing found.  If this cannot
be done, then I would resort to X-rays which can usually differenciate
between PT cables and conventional reinforcing.

If the hole needs to penetrate the pt cable, then I have specified that the
area be chipped out and intermediate anchors are placed on either side of
the proposed hole.  One the anchors are installed, the PT cable can be
safely cut.  I beleive VSL has information about these anchors (as do some
of the other suppliers I'm sure.)

As far drilling through or into the cables.  I have been lucky enough to not
experince what happens when the cables are drilled, however, I have seen
them break during stressing and it is something to avoid.  The release of
25+ kips of load can result in a number of unwanted events, including, I am
told, the cables shooting ot of the slab!

John F. Jones
Winzler & Kelly Consulting Engineers


At 03:36 PM 3/28/98 -0700, you wrote:
>I am on a committee to answer questions asked in Structure Magazine
>published quarterly by the National Council of Structural Engineers
>Associations.  I am asking for responses to be sent to me at
>loveengr(--nospam--at)msn.com so I can summarize them and come up with a consensus of
>opinion.
>
>1.  Occasionally it is necessary to drill holes through post-tensioned slabs
>for anchor bolts and sometimes 6" diameter holes.  Can holes be drilled
>safely without  breaking a cable?  What happens if a cable is broken?  Are
>there other methods of detecting cables besides radiographic inspection?
>
>Sam Love
>Love Engineering
>Ogden, Utah
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