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I was under the impression that the limiting crack width for crack control 
*was* taken at the surface, not at the reinforcing steel.  But, regardless, 
if grade 40 reinforcing will work with *much less* reinforcing than crack 
control would require for Grade 60, then *something* is wrong.  If you put 
the same amount of Grade 60 reinforcing in as would be required for Grade 40, 
then the stress in both (and the strain) would be the same for the same 
load.  Therefore, the cracks should be the same width, both at the 
reinforcing level and at the surface.  Remember, for crack control, we are 
talking about *service* loads, not ultimate loads.

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

Bill Allen wrote:

. > I believe the provision is to limit the width of the crack. At a given
. > strain level in the reinforcing, the crack width at the surface of the
. > concrete will be wider if there is more cover.
. > 
. > Regards,
. > Bill Allen
. >