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WWM vs WWF
2

WWM vs WWF

WWM vs WWF

(OP)
Sounds like pro wrestling, but my question is:  Is WWM the correct designation for welded wire fabric (mesh)?

Thanks.

RE: WWM vs WWF

No, it's WWF.

RE: WWM vs WWF

Actually I think it is changing to Weld Wire Reinforcement.

RE: WWM vs WWF

I usually use MIG.




"mashed into the ground"

RE: WWM vs WWF

JAE, I was thinking WWC, welded wire crap... for the same reason you describe!

RE: WWM vs WWF

lol WWC... I can't wait to use that one

RE: WWM vs WWF

mashed into the ground except for the part that gets pulled upward with a crowbar between the guy's feet.

RE: WWM vs WWF

....while the guy is standing on the WWC...ya...sure...it gets pulled up OK.

sure...

RE: WWM vs WWF

I always chuckle when they tell me they pull up the wire mesh...

RE: WWM vs WWF

WWF properly specified and installed on continuous chairs is cost effective when compared to reinforcement of deformed bars.  Poor engineers specifying 6"x6"-#10x#10 deserve the results they get.

RE: WWM vs WWF

After 28 years of harping on contractors, specifying chairs, etc. and not getting it....well....I don't deserve it - so WWF doesn't get specified by me for on-grade conditions.

RE: WWM vs WWF

Our office usually calls for the WWR to be tied to #4 @ 48" ea. way. When it is something substantial (like #4 bars), chairs are usually installed which places the reinforcement at the correct location.

RE: WWM vs WWF

WWC...that's a new one for me (and pretty funny at that).

i never understood why it's so hard to get the stuff up off the ground. in my contractor days, we supported the wwf at 4' o.c. and still had someone going around during the pour pulling up the areas in between. it wasn't rocket science and didn't take that much time/effort to do.

i like to see the heavier guage stuff specified if at all. at least the industry has moved away from that rolled up crap that would tear you up if the guy on the roll end let it go after rolling out about 20' of the stuff and you were on the other end (end that the stuff rolls up toward like a wound up spring). however, it did make for some comical scenes at times (thank goodness i never saw anyone seriously hurt).

RE: WWM vs WWF

msucog,
The problem with pulling up WWC (heh) is that there is NO way to provide quality assurance that you are getting what you ask for.

The wire fabric cannot be seen, it is being stood on by the workers who have no direct control over the height of the wire in the concrete, and then step over it again to get to the next area.  This is absurd and goes against everything recommended in ACI in terms of placing reinforcing in a secure fashion prior to placing concrete.

RE: WWM vs WWF

This has come up many times in this forum, but my 28 year structural engineering experience has taught me not to specify it, or detail it ever again.  It does not do what they purport because it NEVER ends up where the detail drawing shows it is supposed to be.

I know there are two distinctly divided schools of thought on this one, but I will never cross the line again with this welded wire crap.

welded wire crap is exactly right.

RE: WWM vs WWF

oh i agree completely. however, if supported at 4' o.c., i feel comfortable that it is "more or less" in the middle of the slab (more than if not supported that is). we core slabs all the time and 90% of the time, the wire is on the bottom (exposed on the bottom side of the core that is) because they're never supported. if the heavier guage stuff is required, at least it's too rigid to bend much under the weight of the workers when supported at close spacing. my concrete professor taught us that the wwf was just to help hold the cracks together to some degree...but absolutely shouldn't be counted on for anything else unless it is the heavy guage stuff. i definitely prefer to see reinforcing bar specified.

RE: WWM vs WWF

I've taken too many cores with the WWM/F/R located at the bottom of the slab.  I spec rebar to be located with 2" top cover... works fine as long as it is chaired properly...

Dik

RE: WWM vs WWF

Just to be contrary, as is my wont, the reinforcing in a slab on ground does more good in the bottom (but not in the dirt).  The applied force due to restraint is at the bottom, so that is where the crack starts.

RE: WWM vs WWF

Hokie, I disagree. The steel is more for shrinkage and temperature changes. The top of the slab releases its moisture much faster than the bottom of the slab (usually against a vapor barrier). The release of the moisture causes shrinkage in the top. Since the bottom is restrained and the top tries to move, a crack forms at the top of the slab.

In addition, who cares if a crack forms in the bottom. Nobody will ever see it. You want to control the crack dimension where it is visible (on the top).   

RE: WWM vs WWF

Tngolfer, I acknowledge that your view is the majority one.  But the problem with it is that shrinkage and temperature change (both volume changes) do not cause concrete to crack, restraint does.  The restraint is at the bottom, so that is where the crack initiates.

If you are interested in thinking about this more, there is an excellent paper in the July 1997 issue of Concrete International, "A Structural Looks at Slabs on Grade" by Cesar Kiamco, which explains it in detail much better than I can.

RE: WWM vs WWF

But, as tngolfer says, if the bottom of the slab (with its mesh) restrains the top, couldn't cracks then form in the top without extending to the bottom?

I guess I'll stick with the traditional.

RE: WWM vs WWF

As the slab tries to shrink, you would get a "smiley face" deflection if the ground wasn't present and you would have tension in the bottom. Since the ground is present and won't allow the slab to deflect, the top still tries to shrink but the bottom will not allow it. This causes a crack to form in the top. One large crack would form at the weakest section unless you have steel to limit the crack width and create many small cracks. If the steel is in the bottom you would still get one large crack.  

RE: WWM vs WWF

I don't expect to convince many people, but if you can get access to Kiamco's paper, it is at least thought provoking.

RE: WWM vs WWF

The concrete work I've seen in Australia has the mesh pretty much where it is specified.  It seems to get properly chaired though.

RE: WWM vs WWF

I'm a Canadian Structural and did my intership in Ontario.  While there my experiences were pretty much the same as JAE's expression of "harping", however now that I work in New Zealand I never have problems with chairs anymore.  The finite attention paid to concrete detailing here (due to the very serious seismic considerations) means that contractors do not expect to get away with much, and don't really try.  Chairs are almost always in place, the chairs are securely tied and you can walk on the mesh without much deflection thanks to the normally quite generous number of chairs supplied.  And it's always chairs too, not small pieces of brick or other junk from around site! *sigh*  And in case you're curious, WWR is simply called "reinforcing Mesh" and abbreviated "Mesh" in a soft metric system... ie 6x6 6/6 becomes 665 MESH (only approx equal).

While I find that with concrete work the quality is in general much better here than in Canada, that's not to say that everything is better....

Most steel quality if comparable between the two countries, and falls into the classic (pretty much always good out of the shop, usually good on site), timber is again the same with good quality work being the norm, and the occasional horrifying nightmare job being the exception to the rule.

That said, Site Safety is no where near as good here in New Zealand as it was at home.  Also awareness is very different, and the guys here on site often chuckle and call me a "blouse"; Sort of a polite/teasing "You're a girl" when I wear safety gear.  Except for the once in a while someone gets hurt while I'm still there.  Always happy to help with the first aid when that happend... *evil smile*

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

RE: WWM vs WWF

The twists and turns of this thread.  From designation of reinforcing, which is apparently different in every country, to where it is best placed in a slab on ground, and to quality in different places.

We use a lot of reinforcement mesh in Australia, both in slabs on ground and in suspended slabs.  Probably because it is used so much in suspended slabs, our workers seem to give it as much respect as bars in terms of placing accuracy.  Our standard bars are now deformed, 500 MPa, and the standard sizes are 5, 6, 6.75, 7.6, 8.6, 9.5, 10.7, and 11.9.  Square meshes are usually at 200 centres each way.  Rectangular meshes with the main bars at 100 centres are readily available for one way slabs, and special orders are often done for large projects.

 

RE: WWM vs WWF

Hokie66, I appreciate your reference to the article by Kiamco.  I have noticed over several years and millions of dollars of construction that it doesn't seem to matter where the wwf is in the slab - it still seems to be effective.  At least, better than no wire or plastic fibers.  I understand the frustrations of those trying for an exact placement - still, it's a pretty forgiving product.  

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