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Square Reinforcing Bars

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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
stress?

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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