Rebar Yield Strength in 1956

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thread507-391764
This is for CRSI/US but might help for Canada.

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I believe that it most likely was 50 ksi by 1956 in Ontario, but if there is no one who can confirm one way or the other, then we would have to do some tests of the steel...either that or assume 40 ksi for now. Thanks for the comments. Much appreciated.

I believe in Toronto, Ontario, we specified intermediate grade (40 ksi) in 1956 but it may have tested higher than that.

See thread507-256115

BA

Hi BARetired;

Are you quite sure of that? After posting my question, I did some research and found that the 1956 Toronto Building Code (we have copies of various years of Toronto Building Code in our office) says that for an allowable steel stress of 20000 psi, the steel grade was hard grade. Hard grade has always been 50,000 psi yield. The 1945 Toronto Building Code also said this, as did the 1956, 1957, 1958 Toronto Building Codes. However, sometime in the 1960's the Toronto Building Code was changed to say 20,000 psi working stress was ok for intermediate grade (which would be 40000 psi yield). Since we know from our microfilm archives that this building was designed in 1956 and at least the first phase of it was built in 1957 (although we do not yet know when the later phases were built)it seems most likely that it was hard grade (50000 psi yield) steel at least in the first phase. However, to be safe, I am checking it as though it were 40,000 psi unless some tests are done. It might also be of interest to see what the NBC said around 1956...I will see if I can find that.

Thanks for your response. I always look forward to hearing from you. Your one of the people on this system who always stays on topic and has wise advice.

Hi ajk1,

Thank you for your kind comment. I cannot say what others did at that time, but I am quite certain that, as a junior engineer in my first job in a structural design firm, I specified intermediate grade steel in 1956 in the belief that a higher strength steel was too brittle to be used as reinforcement.

BA

It's not a clean parallel by any means, but I happen to know an interchange in Montreal in 1965 used intermediate grade.

ok, than you both for this information. Very much appreciated.

Attached are the cover page and the page giving the allowable rebar stresses, from the 1956 Toronto Building Bylaws.
This says that:
if hard grade (50,000 psi yield) steel is used, then the allowable stress was 20,000 psi;
if intermediate grade (40,000 psi) steel is used, then the allowable stress is 18,000 psi;
if rail steel bars are used, then the allowable stress is 20,000 psi.

For those who remember working strength design, the area of steel required was
M / 1.44 d for 20,000 psi allowable
and
M / 1.29 d for 18,000 psi allowable.

where M is foot kips and d is in inches.

Some years later, the Toronto by-law was changed to say that the allowable stress was 20,000 psi for intermediate grade steel.

I do not yet know what the yield strength was for rail steel.

Further to my above posting, I see that the same provisions applied in the Toronto Building by-laws up until and including 1962. In 1963 it was changed to say the allowable steel stress was 20,000 psi for billet steel bars of intermediate and hard grade (as well as for rail-steel bars).