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Re: Coring concrete slab

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Tom,

If might want to check out Ground Penetrating Radar.  It is not not as
detailed as Pachometer survey or X-ray, but may be cheaper since it is
somewhat automated.  There are limitations.  A good GPR operator may be able
to answere this questions yes or no.

Arvel L. Williams, P.E.

Tom Castle wrote:

>  Help!
>
>         I am working on a seismic retrofit of a group of residential
> timber framed buildings over a mild reinforced concrete parking flat
> slabs.  We are adding a lot (over 1,000) hold down rods through the
> deck.  Our plans show drilling through the 12 inch slab and placing a
> square plate washer on the underside of the slab.  The project is
> located in the City of Los Angeles.  I mention this fact because I
> believe this precludes the option of using epoxy anchors into the slab
> due to the low allowable values in the City and the relatively high
> loads (as much as 25,000# tension).  I specified on the plans to verify
> by nondestructive means the rebar location before drilling.  I did not
> want to cut any rebar because the slab appeared to need all it could
> get, specially with the new loads that could be imposed on it.
>
>         The contractor "saved" the client $40,000.00 by deleting the
> pacometer tests to find the rebar.  He used a roto hammer to drill the
> holes and stopped if rebar was hit and moved the hole.  That was fun and
> it worked for the first couple hundred holes.  Then came a portion of
> the project located next to the electrical feed panels.  When the roto
> hamer hit them, the lights went out before the drilling could be
> stopped.  They tried the pacometer at this point but said that it would
> not detect the bottom bars or the bottom conduit.
>
>         Their current thought now is to X-ray the slab at $120.00 per
> location at night (because no workers are allowed within a certain
> radius while the X-ray is working).  I have asked repeatedly if there
> was another method of nondestructive testing that could be employed.
> They say no.  I can't help but think in this day that someone has
> developed some device that could be used for this purpose that does not
> require the expense and inconvenience of the X-ray.  Has any one seen
> any thing?  It's really the contractor's problem, but it would make the
> job go alot easier if we could figure something out.  Thank you for any
> thoughts.
>
>         Thomas Castle, S.E.
>