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RE: Rebar Strengths

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At-place Load Test would be a prudent thing to do. This test may be done on a small representative panel of the slab per se only. 

By the way, you mentioned about vertical rebars extending, out of the top of the columns, for future lap splices. This is very unusual thing to do, in my opinion. Such rebars, for future lap splice, are always embedded in: either under the slab (if the roof is intended to be used, so have to be kept free of any protruding pedestals) or in a protruding pedestals, otherwise, to protect from corrosion.

If that is the case, described by you, I am afraid you must be having a serious corrosion problem by now. In this case, you have another important assignment to settle first; that is to to investigate the extent of corrosion in these vertical rebars. Best regards,

Syed Faiz Ahmad; MEngg, M.ASCE
Senior Structural Engineer
Saudi Oger Ltd
Riyadh, Saudi Arabia.

-----Original Message-----
From: Jason Kilgore [mailto:jkilgore(--nospam--at)]
Sent: Wednesday, October 22, 2003 10:45 PM
To: seaint(--nospam--at)
Subject: Rebar Strengths

I have a reinforced concrete building constructed in the "early 1920's".

The existing roof was obviously designed to carry future floor loads after
vertical expansion of the building (it's flat with a sloped wood overbuild
for drainage, vertical bars extend out of the top of the columns for future
lap splices, and the columns are relatively massive - 20" hexagonal columns
supporting less than 350 sq. ft. of roof).

Now, the owner wants to add some stuff to the roof.  What I need to to is
determine the capacity of the roof.

There was some testing done, and I have representative rebar information
(size, spacing, cover, etc.) throughout the building.  Also, cores were
taken (corrected f'c varied from 3640 to 4420 psi.  Unfortunately, no
testing was done on the rebar strength.  I know that some of the bars are
round and some are square.

Does anyone know what strength of rebar was used back then?  I have tons of
references concerning steel beams, but none concerning rebar.

Thanks for your help,

Jason Kilgore
Leigh & O'Kane, L.L.C.
816-444-9655 (FAX)

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