huangyhg

synthetic fiber reinforcement
a contractor would like to use synthetic fiber reinforcement in lieu of wire mesh for use in treads of a metal pan stair.
is there any way of comparing the reinforcement area between the two?
no, used for different purposes. synthetic fiber for micro cracking vs steel for tension in flexure or shear strength.
since the metal pan provides the structural support for the concrete wearing surface, the reinforcement serves to provide crack control. fiber is an excellent choice in my opinion. too often, wwf gets pushed down to the bottom of the typical slab.
i don't know how big your treads are. if they are 11" deep, then the wwf would only be effective in controlling the cracks in one direction.
the treads are only 2" to 2.5" thick. the metal pans serve as the structure. the synthetic fiber reinforcement would only be used to control cracking.
i never specify reinforcing in metal pan stairs unless the treads are quite long, in which case i would use a couple of reinforcing bars. the fiber would do no good.
how much shrinkage do you really get in a little metal pan stair? is the reinforcing even necessary? (i'm with hokie66 on this one).
first of all, grace's fiber, strux 90/40 is one of the few fibers rated to provide flexural capacity for slab on grade situations. it replaces wwf in slabs on grade. grace provides an equivalent dosage rate for a particular wwf replacement.
that being said, since you're elevated you cant use strux as anything for flexure. if you just want it for durability on the tread concrete, i dont think you would get good results with bars or wwf. for durability, i would use any fiber that finishes well....and make sure the metal tread pan can support the full load.
for stair landings with intermediate supports, i would resort to properly chaired bars or wwf to resist any negative moment. do not let them sub a fiber in the landings otherwise you risk getting cracks above supports.
in a metal pan stair, i would use the pan only as a concrete form, and rely on the tread embedded rebar to do the work for the tread.
the reason i say this is i ran into one system in an aprtment building a few years ago where the pan had rusted out at the stringer location and the only thing holding the stair tread was the rebar. this happened in several locations on the stair assembly. rusting can happen very quickly with salt on the exterior stairs of apartments and office buildings due to snow accumulation.
just a thought.
mike mccann
mccann engineering
i disagree with mike. a steel pan stair with steel channel stringers of course has to have a corrosion protection system appropriate to the environment just as any steel structure. but using the concrete in the pans structurally is not the answer. if you want a concrete stair, build one.
hokie66:
i guess we have to agree to disagree here. my experience tells me otherwise. no worries mate.
mike mccann
mccann engineering

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