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RE: Subgrade Drag Equation

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Is it true that shrinkage control reinforcement does not get mobilized until the concrete cracks?

It is worse than that. reinforcement in concrete actually induces tension stresses in the concrete, adding to the subgrade restraint stresses, increasing the likelihood of cracks. It only starts helping after the concrete cracks.

If they really want a large joint-less surface, would PT work? I imagine that a PT SOG would cost more than adding a few extra joints though.

PT is often used in Australia for crack free slabs on ground. But you have to put in enough PT to keep the stresses very low. Many of the PT SOG's in the US use too little PT and the slabs crack anyway.

From: Mark Puccio [ mailto:mpuccio(--nospam--at)]
Sent: Monday, May 11, 2009 12:09 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?

Regards  Gil Brock
Prestressed Concrete Design Consultants Pty. Ltd. (ABN 84 003 163 586)
5 Cameron Street Beenleigh Qld 4207 Australia
Ph +61 7 3807 8022               Fax +61 7 3807 8422
email:            gil(--nospam--at)
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