wwf vs rebar

huangyhg

wwf vs rebar
can anyone tell me which system you prefer and why?  i hear this thing go back and forth about wwf not being installed properly, however it cost much less.  i'm working on a design-build project where cost is very important but i'm not sure everyone will buy off with a cheaper solution should quality be effected.
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i always specify reinforcing bars instead of wwf.  the wwf takes less effort to lay it out, but always ends up in the bottom of the slab where it does absolutely no good.  i've tried to support the wwf on blocks, chairs and bolsters but all that accomplishes is creating a trip hazard for the laborers.  rebar at 16" o.c. each way allows plastic chairs to be used, everyone can put their feet between the bars to walk around.  most contractors i work with like it even tho the bars take longer to place.
wwf is a fine product if installed properly, and it does do something even at the bottom of the slab - unfortunately its not crack control.
just ask any demo contractor who has demo'd a slab without reinforcing and one with wwf.
rebar is however hands down better for crack control.
i use rebar, and reduce or eliminate the control joints.  when using rebar, does anyone see any point in adding fibers to the mix?
i think adding fibers to the mix is a waste of $$.  if the slab is for pedestrian use only, like a normal office, i've used fibermesh but put sawed joints (or a construction joint where it made sense) at 10 ft on center each way.  that seemed to help with cracking between the joints.  using fibermesh with sawjoints or construction joints at a greater spacing resulted in some cracking between the joints.  based on conversations with a contractor that i've worked with on several different projects where we used either fibermesh or rebar in a slab-on-grade, he prefers rebar to the extra sawcuts and fibermesh.
in my previous post, i meant using fibers with rebar is a waste of $$.
fiber and reinforcing do different things.
fibers are for plastic shrinkage crack control (shrinkage that happens when the concrete initially loses its water) and durability (impact resistance).
reinforcing is for crack width control.
its interesting that we structural engineers tend to do one or the other when they arn't for the same thing.
if i'm hard on a project for money, i use unreinforced slabs with a tighter control joint spacing.
i hardly ever use fibers on exposed concrete surfaces, unless they're the kind of fibers designed not to be seen.
i prefer rebar, but if you need to use wwf for cost control, here are several documents (free. pdf downloads) on how do use it correctly
my experience with wwf is disastrous.  the stuff never ends up where you want it. the contractor had to remove portions of some flat work that had gotten away from him during the finishing process.  during the removal of a 50' square portion of concrete, the wwf was at the bottom of the slab not doing a damn thing for which it was intended. i like the fibers for the micro cracks. i always mildly reinforce all slabs on grade even if it is #3 bars.  joint spacing is the most critical element taking special care around re-entrant cornerns.  there have been voluminous studies done about the spacing of control joints based on concrete thickness, etc.  you can check aci, and pca.
what about wwf used in elevated slabs with metal decking? has everyone had similarly disastrous results?
most metal floor decking product catalogues seem to give capacities based on wwf reinforcing.