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Re: Old rebar

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Coincidentally, I had today searched out a 1997 PCA "Engineered Concrete
Structures" article titled Reinforcing Bar Specifications 1911 through 1968.
Here's a quote of a paragraph that may be helpful:

"The first Standard Specification for Billet Steel Concrete Reinforcing was
adopted by ASTM in 1911, revised in 1914, designated A15.  The A15
Specification had three classes of bars: plain, deformed and cold-twisted.
The plain and deformed bars were specified in three grades: structural,
intermediate and hard.  Cold-twisted bars conformed to structural grade
only.  Section 2(a) of A15 stated, 'the basis of purchase shall be
structural grade unless otherwise noted.'"  [An accompanying table gives for
yield min, psi: structural 33000, intermediate 40000, hard 50000,
cold-twisted 44000; tensile, psi: structural 55000, intermediate 70000 hard
55000, cold-twisted n/a.] "Deformations were not standard, and in fact very
dissimilar compared to present markings.  Most were patented and particular
to the producing mill, and were labeled cup, corrugated, lug, herringbone,
or by the name of the inventor .   .   .   .  Bars sizes were also not
standard, with each manufacturer publishing a list of sizes available from
that mill.  Shapes were round, square, oval, flat with either raised lugs or
depressed dimples.  A conservative estimate of steel grade for the
reinforcing bars furnished for a concrete structure built between 1910 and
the mid 1920's would be structural grade. "


Nels Roselund
Structural Engineer
South San Gabriel, CA

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