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RE: Crack control in slab

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Do you mean "expansion" joints or "contraction" joints?  Expansion joints
are usually only located every few hundred feet, and only where there are
temperature extremes (highways, etc.).

Contraction joint spacing depends on:
  Thickness of slab
  Type, amount, and location of reinforcement
  Quality of concrete and curing, and environmental factors (humidity, wind)
  Base friction
  Slab restraints and discontinuities

If it's a heavily reinforced slab, with the steel with 2" of the top
surface, you probably don't need contraction joints (rho > 0.005).

ACI's "Designing Floor Slabs on Grade" and 224R-01: "Control of Cracking in
Concrete Structures" might be of help.  They are available at the American
Concrete Institute's web site.


-----
Jason Kilgore
Leigh & O'Kane, L.L.C.
(816) 444-3144
jkilgore(--nospam--at)leok.com


-----Original Message-----
From: Samir Ghosn [mailto:sghosn(--nospam--at)harris-assoc.com]
Sent: Monday, March 11, 2002 11:15 AM
To: seaint(--nospam--at)seaint.org
Subject: Crack control in slab


Hi friends

I am interested in some feed back on spacing of expansion joints in a slab
on grade supporting 65,000 Lb Gross Vehicle Load, the slab is 8 inches
thick, reinforced to account for loading using beam on elastic foundation
theory, using K=180 pci.  My initial thought was to have a spacing about 10
t0 12 feet.  Am I on the right track here?.
The Slab will have a 4 inches  of class II aggregate per Caltrans
specification over an 18 inches of subgrade compacted to 95 percent.
Your input is greatly appreciated.
Samir Ghosn, P.E.
Harris & Associates
(800) 827-4901
fax( 949) 655-3995
e-mail " sghosn(--nospam--at)harris-assoc.com"



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