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RE: ACI - Z cracking
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: ACI - Z cracking
- From: "Scott Maxwell" <smaxwell(--nospam--at)umich.edu>
- Date: Mon, 19 May 2008 14:24:23 -0400
for correcting me on ACI 350. Since I am not a "tank" guy, I don't keep up
with it. I only knew about it because I was staff liaison to the 350
committee when work for ACI many, many moon ago.
I believe that ACI 318 replaced the z-factor in the
1999 code. There is still a requirement related to spacing of bars to
control cracking, but it is less stringent and is based on aesthetics rather
The ACI 350-01 code retained the z-factor equations
to control cracking for durability. The ACI 350-06 code modified the
crack control equations, replacing the z-factor equations. The modified
equations are based on research by "Frosch" rather than the previous
research by "Gergely-Lutz". The equations in ACI 350-06, Section
10.6.4, were reformatted to calculate an allowable steel stress based on bar
size and spacing in lieu of the quantity 'z'.
CH2M HILL /
cracking in ACI 318 went "bye-bye" quite a while ago (I want to say in the
1999 or 2002 edition, but I would have to look it up to be sure). It
has remained in the ACI 350 code document to my knowledge (it is a "variant"
of 318 for environmental structures...aka tanks...they are now independent
of ACI 318, but they still tend to use 318 as a basis, but have choosen not
to follow on something...such as dropping the Z cracking
2005 ACI revised 10.6.4 to give max spacing
versus the old Z cracking formula? Sounds like this was based on a lot of
recent research. My ole 95 version from college still has the Z cracking
formula and Enercalcs older versions use it in the beam design under
Andrew Kester, P.E.
ADK Structural Engineering, PLLC
1510 E. Colonial Ave.,