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Square Reinforcing Bars

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John,

Square reinforcing was gone before I took concrete design in college (1958).  
The ACI code in effect then was the 1956 code.  But, you are right; #9, #10, 
#11, #14, and #18 bars have the equivalent areas of 1", 1-1/8", 1-1/4", 
1-1/2" and 2" square bars and were frequently shown on bar charts as a circle 
within a square.  #14 and #18 bars were frequently shown as #14S and #18S, as 
"Special Bars."

Reinforcing with an allowable working stress of 20,000 psi generally had a 
yield strength of 33,000 psi; the allowable stress being .6F(y).  However, 
don't try to compare the adequacy of the design by using USD.  For one thing, 
the bond stress was used to determine the embedment length or splice length 
of a bar based on the *stress* in the bar at that location under service 
loads, not to develop the strength of the bar as is done under USD.

If the specs/notes indicate that the reinforcing is to conform to ASTM A15 
*and* A305, the bars were supposed to be deformed.  A15 specified "plain and 
deformed" reinforcing requirements and A305 specified deformation 
requirements.

The only "plain" bars that I have spec'd under A15 were column spirals.

It seems that we have gone full circle with regard to specifying plain bars.  
A615, when it replaced A15 specified only deformed bars; now, the latest A615 
covers both plain and deformed bars.  Once again, if you want deformed bars, 
you have to specify "*deformed* bars conforming to A615."

HTH

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

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
. > 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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