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RE: Rebar Strengths

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This is tricky.  You may have difficulty making that slab meet current
code requirements.  I've worked on a number of 1920-1930 industrial
buildings.  Typically I deal with the steel which is A7 or A9.(don't
weld to it)

For concrete structures of that vintage, the bars are typically smooth
and can be rectangular.  I have used 30 ksi as my yield stress, and
conservatively use 2,000 psi for concrete strength.  I found some
ancient reference manuals.  The designs typically were "off the shelf",
that is, designs came from tables as opposed to calculations.

Most of the "early" designs I have seen came out of New York and Salt
Lake city by a company called "The general engineering company
consulting engineers".  I've tried to track them down to see who now may
have possession of their in-house design procedures.  It would be an
interesting read.

I recall one slab where the reinforcing was not continuous over the
supports, it was essentially a series of hammocks. 80+ yrs of heavy

Sounds like an interesting project - enjoy.

As food for thought - depending on the use over the years, I would watch
for chemical attack on the rebar, splice lengths and would try to get a
test on some rebar.

Hans E. Boge, P. Eng.
Boge Boge (1980) Ltd.
268 Ellen St., Wpg. MB
R3A 1A7, Canada
ph: (204) 942-7276
fx: (204) 942-7288

-----Original Message-----
From: Jason Kilgore [mailto:jkilgore(--nospam--at)] 
Sent: Wednesday, October 22, 2003 2:45 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
vertical expansion of the building (it's flat with a sloped wood
for drainage, vertical bars extend out of the top of the columns for
lap splices, and the columns are relatively massive - 20" hexagonal
supporting less than 350 sq. ft. of roof).

Now, the owner wants to add some stuff to the roof.  What I need to to
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
round and some are square.

Does anyone know what strength of rebar was used back then?  I have tons
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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