concrete working stress in early 1900's building codes

[gte447f]

I have a small concrete repair project that involves a building originally constructed in 1901. I have been researching building codes from that era and have come across limits on working stresses for compression in concrete of around 230 psi, which seems very low to me. Is this the stress limit that would have been used for extreme fiber stress in compression for design for flexure using working stress design at the time? Or, might this be the limit for the average stress in compression for the triangular stress distribution of the working stress method, in which case the extreme fiber stress in compression could be 2 times the average?

I am questioning the 230 psi working stress limit because it seems very low compared to the more familiar 0.45*f'c limit that seems to have started to appear in codes a couple of decades or so later for exterme fiber stress in compression for flexure. Hopefully someone here who is more familiar with historical design of reinforced concrete than I am can offer some guidance.

 

[CANPRO]

gte447f, see attached. Might be helpful.

 

[dhengr]

Gte447f:
Since you are already going to be doing rehab. and repair on the bldg., why not take a few core samples at locations which can be patched during your repair work? Then, test these samples and you will really have some thing you can hang your hat on. Guessing at what the conc. strength is for 118 year old conc. seems like kinda a fools game. I’m seeing allowable compressive strengths for conc. double or triple your 230psi, in the early 1920’s. I would think that your conc. condition and durability after 118 years should be a good indicator that it can be incorporated into the repair, using fairly low f’c values, if you don’t want to test.

 

[gte447f]

CANPRO, thanks for the reference. The value of 750 psi equates to 0.375*f'c for 2000 psi concrete and the other value given is 0.325*f'c.

I think the value of 230 psi that I am seeing in some codes around 1900 must be be very conservative to address all concrete including lean mixes like the 1:3:6 mix in your reference's table and cinder aggregate mixes like the ones in your reference's table.

dhengr, at this stage, this particular project is pretty small scale, and coring and testing are not in the scope of work. After I make some recommendations to the owner, things may change. I am just trying to get an idea of the basis of the original design. Lacking any other information, I would have assumed f'c = 1500 psi and fy = 33 ksi per ACI 562-16 chapter 6. It turns out, the owner says they have some original construction drawings, which is shocking, but I am going to look at what they have.

The 230 psi working stress comes from a copy of the 1911 Atlanta building code. In looking through the document a little more thoroughly, I came across a section addressing reinforcing concrete where they give 800 psi for extreme fiber stress in compression due to flexure, which sounds a little more normal to me.