Rebar grade in 1920s? 1

[WWTEng]

I have a small renovation project from 1928. I can't find the material properties in the existing drawings. Would it be reasobale to assume f'c= 3000 psi, fy= 40,000 psi?

 

[CANPRO]

seems like this has been covered before. The link in the other thread covers the era you're looking for.

http://www.eng-tips.com/viewthread.cfm?qid=252569

 

[briancpotter]

Can you give more information on the building? Layout, structural members, etc?

References from that era give material information as working (allowable stresses). For steel, the minimum acceptable stress was fs = 16,000. Steel varieties varied quite a bit, so it's difficult to be more precise than that.

For concrete, there also appears to be quite a bit of variation. I'm seeing numbers in the range of fc = 600-650, which is quite low. It might be worthwhile to perform a swiss hammer test instead of trying to guess at capacity.

This is from this book:

http://books.google.com/books?id=ui...ed=0CEYQ6AEwAjgU#v=onepage&q=concrete&f=false

. Do a google book search on "concrete" or "reinforced concrete" between 1920 and 1930 for more (free!) references from that period.

Brian C Potter, PE

http://simplesupports.wordpress.com

 

[UcfSE]

Try this, maybe it will help.

 

[WWTEng]

Thanks all.

I guess it would make sense to do some testing to figure out the existing capacities. I know they can do core samples for concrete, but is there a way to test the existing rebar?

 

[bridgebuster]

You could test a piece of rebar. AASHTO allows 18,000 psi for unknown steel. If you look in old text books as pointed out above you can get a feel for what our ancestors did.

I agree with the core. I've done some building renovation and learned concrete strength is over the place. Plans back then usually didn't specify f'c, they just went with a mix proportion. Same thing with old bridges.

 

[WWTEng]

UcfSE, the link is very informative, thanks. It appears that for the era in question (1928) rebar could be anywhere from 16, 18, 33 or 40. I think testing might be the only option, so again my question: can they do testing on existing rebar to figure out the yeild?

Thanks.

 

[UcfSE]

They can do tests, but you may be better off assuming grade 33 to be safe. Note the 16 and 18 are allowable stresses based on the rebar grade, not the actual rebar grade itself. 16 is structural grade (33), and 18 is intermediate (40) and hard (50).

Note also that if you do tests, you can't use the direct results of the test. The test will only help you ascertain which spec or grade you meet, or what ASTM spec you meet (if you use astm). Once you can evaluate the astm spec you meet, you can use that spec's minimum yield.

 

[BAretired]

It appears that for the era in question (1928) rebar could be anywhere from 16, 18, 33 or 40.

You are mixing allowable stress with yield stress. The yield is likely to be 33ksi. The bars are probably plain (undeformed) and may be square or round.

Tests can be done by removing a sample. I don't believe there is any test to determine yield for steel in place.

BA

 

[WWTEng]

BA, UsfSE: Yup, made a mistake there. Thanks for correcting me.