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RE: Concrete and rebar strength

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> -----Original Message-----
> From: Kestner, James W.
> I am adding loads to a building built in 1930. Amazingly, we have
> found the existing drawings and specs!
> There is no compressive strength specified for the concrete.
> However, it specifies a concrete with 1 part cement, 2 parts sand
> and 4 parts aggregate. Can I tell from this info., what the 28
> day compressive strength may be?
> Also, the rebar is Federal spec. 350A, type B, any grade or class
> except structural grade. Can I tell from this info. what the
> particular yield strength is?
> Jim K.

Concrete was traditionally specified this way in the UK. My only reference
is the 1969 edition of CP114, from which I've extracted the following:

A 1:2:4 mix would give a 28 day cube strength of 3000 lb/in²

The allowable stresses for this mix would be:

Bending compression	1000 lb/in²
Direct compression	775 lb/in²
Shear				100 lb/in²

(all in accordance with UK allowable stress design practices)

There is no direct relationship between cube strength and cylinder strength,
but from various sources a factor of 0.8 is valid (the factor varies with
cube size, concrete strength, etc.)

which implies a cylinder strength of 2400 lb/in²

For reinforcement there is an article:

Reinforcing Bar Specifications 1911 through 1968

that was published in:

Engineered Concrete Structures, Vol. 10, No. 3 (PCA PL279, 1997)

that gives a lot of history, but only references ASTM standards. It
summarizes as follows:

In conclusion, it is reasonable to assume that a reinforced concrete
structure built in the period 1910 through 1927 was reinforced with
structural grade (Gr 33 or 228 MPa yield strength) deformed reinforcing
bars, and from 1928 through 1963 with intermediate grade (Gr 40 or 276 MPa
yield strength) deformed reinforcing bars.

Peter James

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