Fibre Mesh vs Welded Wire Mesh 1

[ansys54]

We are considering replacing 6x6 6-6 wwm with fibre mesh in an office slab on grade. We are concerned only with crack control. Does anyone have information on the performance of fibre mesh.

 

[JAE]

We have used it with success for some time. In fact, we do not ever specify WWF for slabs-on-grade unless the owner specifically requests it.

WWF ALWAYS ends up on the ground, exactly where it doesn't do any good.

Now on metal deck slabs, we do use it.

 

[structuresguy]

JAE: Do you ever use steel fiber instead of WWF for slabs on composite metal deck? I want to make the switch, as I have had several problems, both with my designs and others I have investigated, where the WWF ended up right on the deck and did little to control cracking. Obvisouly, you would have to add rebar in areas with negative moment, but the steel fiber should be better at controling cracking that WWF which is sitting on the deck.

 

[JAE]

Honestly, we haven't used steel fibers except for one project where we had a 5" thick slab supported by composite steel beams (no deck - just formed concrete slabs).

The problem was that the slab was used as the floor of a truck dock where large trucks would back into it and heavy forklifts would drive over it. The beams spanned about 26' and were spaced at 11' o.c. The problem was the forklifts created such large deflections in the beams that significant tensile stresses would develop in the slab. We couldn't thicken the slab due to other parameters.

The slab had really cracked up over the years and was replaced once. Our design included adding beams between the existing beams, adding cross support beams below those on new columns, and using a "strange brew" of fibermesh with steel fibers that our rep. had put together for us.

We had analyzed the slab with FEA to ensure that the maximum tensile stress was below fr. The fibers were added just as a second measure to minimize/avoid cracks.

Unbelievably, after all that, the slab still had a few cracks in it.

 

[dbuzz]

I have seen some very bad results, specifically widespread cracking, with steel-fibre reinforced slabs-on-ground and would be reluctant to specify it. In these cases the design was supplied directly to the Client/Contractor by a steel-fibre Supplier.

My main concern is the distribution of fibres through the concrete mix. They can tend to conglomerate and form balls. With mesh at least you can inspect the reinforcement size, spacing and height before the concrete pour.

However, I would consider specifying it to supplement conventional reinforcing where crack control was particularly important, for shotcreting or for non-critical concrete items such as pedestrian paths.