My university textbook, "Reinforced Concrete Fundamentals," by Phil M.
Ferguson (from University of Texas), (John wiley and Sons, Inc., 1958),
has excerpts form ACI 1956 Code. The Vancouver Public Library or the
UBC Library might still have a copy. Ferguson's was the textbook of
choice in those days; any engineer who's old enough may still have a
The following values for fs from this book might be useful:
20,000 psi for rail steel and hard axle grade.
18,000 psi for billet, structural, and axle grade.
50% of Fy for 3/8" or less diameter reinforcing in one-way slabs with
spans not more than 12 feet; but not to exceed 30,000 psi.
40% of Fy for compression, vertical reinforcement in columns but not to
exceed 30,000 psi.
16,000 psi for structural sections.
Don't forget that all designs at this time were based on working stress
method of analysis.
H. Daryl Richardson
John MacLean wrote:
> I'm reviewing an old paper machine frame. The existing design drawings show
> 1 1/4" square reinforcing bars for top steel in some of the beams. The steel
> strength is listed as fs = 20,000 psi.
> Does anyone know anything about square reinforcing bars. Were they always
> plain bars or were they deformed? Our old ACI code (1963) says to use 1/2
> the allowable bond stress for deformed bars when designing for plain bars.
> That seems generous. I notice that the later codes ruled out using plain
> bars altogether or required hooked ends. Any thoughts on what I should allow
> for development length or bond stress for these bars?
> The drawings list an allowable "fs" = 20,000 psi. What sort of yield
> strength would that be equivalent to?
> I've also heard of twisted square bars. Was that common for the larger bar
> sizes? Did it have any effect on development length or allowable bond
> One interesting thing I've found in an old copy of the CRSI Handbook (1962)
> was a comparison of "old" and "new" bars. The "old" bars larger in area than
> a #8 bar were all square. The equivalent of a #11 bar was a 1 1/4 inch
> square bar. That appears to be why a "new" #11 bar is 1.410" in diameter
> rather than 1.375". The 1.410" diameter gives a cross sectional area
> equivalent to a 1 1/4 inch square bar.
> Any assistance would be appreciated.
> John MacLean
> Vancouver, B.C.
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