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Re: Old concrete

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Good idea.  I was planning on doing something similar at some of the extreme situations (4000# units); but, I may need to do the same at the smaller units.  Thanks.
----- Original Message -----
Sent: Tuesday, November 28, 2006 5:24 PM
Subject: Re: Old concrete

        I'm just doing the same thing as I write.
        As I see it you have three options.
1.)     I wouldn't rely on the slab to support new loading without a detailed evaluation including some cores and testing the rebar.  This is expensive and it might not pass; therefore, rule out option 1.
2.)     Build four posts from 4" or 6" pipe, c/w half inch (or so) base plates, of a height to clear any roofing material (a few inches?) and drill anchor them to the slab above the beams.  Build a structural steel framework supported on the posts and designed to carry the roof top units.  It might be prudent to check out the roof beams (it probably is) but I would be very surprised if they didn't pass.
3.)     Repeat of option 2.) but place the posts directly over building columns.  This will take a little more structural steel that option 2.) but will eliminate any need to check out slabs and beams.
        Hope this helps.
H. Daryl Richardson
----- Original Message -----
Sent: Tuesday, November 28, 2006 2:53 PM
Subject: Old concrete

    I am working on adding some roof top units to an existing building.  Date of original construction is unknown.  The roof framing consists of a 4.5" concrete slab on 8"x14" monolithic beams with square columns.  In a few areas, the slab was demo'd previously for added vents, etc.  The rebar is 1/2" square and twisted, 7"oc each way.  Anyone ever seen such?
Brian K. Smith, P.E.

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