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RE: ACI - Z cracking

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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 than durability.
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'.
Bill Sherman

From: Scott Maxwell [mailto:smaxwell(--nospam--at)]
Sent: Monday, May 19, 2008 12:09 PM
To: seaint(--nospam--at)
Subject: RE: ACI - Z cracking

Z 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 method).
Adrian, MI
-----Original Message-----
From: Andrew Kester, P.E. [mailto:akester(--nospam--at)]
Sent: Monday, May 19, 2008 1:13 PM
To: seaint
Subject: ACI - 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 shear.
Just checking...
Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Ave., Suite 301
Orlando, FL 32803