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Re: Slab-on-grade WWF or WWM oops (Now WWR)

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David,

Actually neither of these are correct anymore.  ACI has adopted the term Weld Wire Reinforcement (WWR) at the recommendation of the Wire Reinforcement Institute.

Thomas Hunt, S.E.
ABS Consulting




"David Merrick" <mrkgp(--nospam--at)winfirst.com>

04/02/2004 11:54 AM

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Slab-on-grade  WWF or WWM oops





Slab-on-grade and the welded wire fabric WWF...

** welded wire fabric WWF is structural. Sizes represent a heavier wire than
that of a similar size value for a mesh.

** welded wire mesh WWM is for fencing. Wire mesh is found too many times in
concrete.
     WWM is not structurally tested.
     WWM sizing values intended for WWF, results in less steel than that
required.
     WWM mistakes results in a light weight grid of wire that may not
support a man's weight between support chairs and is more likely to sag to
the bottom of poured concrete. Not even the imaginary sky-hook will fix all
problems from mistakenly using WWM.

The term "wire mesh" wrongly seems to represent a material that is stronger
than structural term Welded Wire Fabric (WWF).

Look for "welded wire fabric" in the ACI index. See ACI 3.5.3.5, ASTM A82,
and ASTM A185. Below are some cut and paste things from some old litigation
cases.

WWM (welded wire mesh) and WWF (welded wire fabric) are different products.
The UBC and ACI recognize and have material specifications for WWF, not for
WWM. The wire size for WWM is specified as wire gauge and the size for WWF
is specified by cross-sectional area. A "6" in WWM (6 gauge wire) has an
area of .029 in2. a "6" in WWF has an area of 0.060 in2 - a 50% reduction in
strength. Material properties such as ductility and strength are unknown for
WWM. Also note that 6 x 6 - w6 x w6 WWF comes in flat sheets and cannot be
rolled up.

Slabs on grade occur at the garages and at some interior locations. The XXX
plans call for 6X6 X 6X6 WWM (Welded Wire Mesh) reinforcement along with
control joints. This reinforcement is not adequate to control shrinkage
cracking but proper control joints should provide adequate crack control. In
units where excessive slab cracking is found, filling with epoxy and
grinding flat should repair the cracks. The plans for BV2 call for 6x6x6/6
WWF (Welded Wire Fabric) which should provide adequate reinforcement for
crack control.

Shrinkage reinforcement or control joints are not correctly specified. The
1985 Uniform Building Code requires crack control in section 2622(a). The
designer has attempted to utilize reinforcing steel for crack control by
specifying WWM (Welded Wire Mesh) as seen in detail 13/A29. The correct
reinforcement to specify is Welded Wire Fabric as described in Uniform
Building Code section 2603(f)2 and in The Uniform Building Code Standard
number 26-6. The 10-gauge wire mesh specified in the drawings provides an
inadequate amount of steel to control cracking as specified in section
2607(m).

The Uniform Building code requires that temperature and shrinkage stresses
be provided for in concrete by either reinforcement or joints (See 1988 &
1991 UBC Sec. 2622.a). The foundation plans do not call for joints in the
interior slab on grade. The foundation plans do call for "w/ 6x6 -10x10
W.W.F" at the interior slabs. WWF refers to "Welded Wire Fabric" and is
described in section 26-6 of the Uniform Building Code Standards. It is
extremely rare to find Welded Wire Fabric in residential construction. What
is typically found is "Welded Wire Mesh" (WWM) which is not an approved
concrete reinforcing steel. In WWF the 10 designation refers to the
cross-sectional area of the wire. Correctly designated, a "WWF6x6-W10x10
would be smooth wires with a cross-sectional area of 0.10 in2 at 6 inches
on-center each way, which is nearly equivalent to #3 bars at 6" each way.
This provides 0.20 in2 of steel per foot. WWM 6x6 10x10 refers to 10 gauge
wires at 6 inches on center or about 0.028 in2 per foot. Shrinkage control
minimum steel is about .086 in2 per foot. Further investigation and
destructive testing would be required to verify the size of the reinforcing
steel.




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