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RE: Subgrade Drag Equation

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Not sure how thick your slab is, but I agree that the proposed rebar and joint spacing "sounds like cracks waiting to happen".  I haven't seen it formally stated in the standards, but apparently the old subgrade drag formula is now in disfavor.
Section 6.4 of ACI 360R-06 recommends joint spacing per Figure 5.6 in that document.  If you want to eliminate such joints, Section 7.3 recommends 0.5% steel.  Section of ACI 302.1R-04 also recommends 0.5%reinforcing steel in order to reduce or eliminate contraction joints.  And Table of ACI 350 for liquid-containing structures recommends 0.5% to 0.6% reinforcing steel for movement joints exceeding 40-ft spacing.  Seems to be a pattern here...
Bill Sherman

From: Mark Puccio [mailto:mpuccio(--nospam--at)]
Sent: Monday, May 11, 2009 4:09 PM
To: seaint(--nospam--at)
Subject: Subgrade Drag Equation

We are working on an industrial farm project that has a large slab-on-ground. All joints need to have waterstop installed, so we have been told to minimize the number to as few as possible.  I was given, by our client, a reference for joint spacing using the subgrade drag equation.  This reference refers to ACI 360 of which I have the ACI360R-06 but do not find this equation in it.  It also shows joint spacing at 79-feet with #4 at 18. Wow this sounds like cracks waiting to happen.  Not wanting to get sued spurs some questions.


Does anyone know if this equation is acceptable with current ACI?

Has anyone used this type of spacing with good results?

Is this in the 360R-06 or where might if find it.

Besides good curing, low W/C ratio what other factors (besides shrinkage compensating concrete $) were used in your successful project?