Slab on grade with steel fiber reinforcement

[SilverBeam75]

Hi,

I have a slab on grade 8'' thick and it will carry heavy vehicle loads, I have specified 15M rebar @ 12'' c/c in each direction. My client is asking me to provide an alternative using fiber steel reinforcement. My question is, how do you calculate it ? what would be the equivalent to 15M ?

 

[Ron]

Fiber is an enhancement to the concrete, not a replacement for reinforcement. There are advantages to using fiber, particularly steel fiber; however, the advantage is an increase in the compressive strength of the concrete, a good increase in the flexural strength of the concrete and some crack control, depending on the fiber type and orientation.

I'm not sure why you have the rebar in the slab, other than for thermal movement, as slabs on grade are quite capable of carrying heavy traffic loads without reinforcement.

 

[PicoStruc]

You can't ! As simple as that !

Fiber reinforcement help for shear behaviour and cracking only Not bending.

Thus in Canada, i don't know any code (right now) that allow to consider fiber reinforcement to reduce stirrup or increase rebar spacing for cracking (less than 500mm)

A lot of research is done in beam shear reinforcement reduction by adding fiber.

This, if your rebar are required for bending you can't do nothing about it !.

If i am mistaken tell me !

 

[hawkaz]

Agree with Ron and Picostruc- You are comparing apples and oranges.

As Ron stated- you might be able to eliminate the reinforcing all together- watch your joint conditions however. I call out dowel baskets and plate dowels at all joints in slabs like this. These help limit curling (which is the cause of a significant amount of slab cracks in heavily loaded slabs)

 

[bridgebuster]

We had a presentation on steel fibers by rep from Bekaert. He said it's possible to get a degree of flexural reinforcement from fibers. Why don'y you give them a call (800 372 6940)? Their services are free.

 

[MiketheEngineer]

Steel fiber is most often used in very heavily loaded floors - esp when using steel wheeled carts.

While I am sure it does provide "some" reinforcement - it's primary use is to temper the surface and protect against these nasty loads.

 

[spats]

Years ago I designed a Vehicle Assembly Building at Cape Canaveral, where we used steel fibers to enhance slab bending. The fibers were manufactured by Trefil Arbed (a European Company), and they had software to calculate the allowable bending based on dosage and the specific type of fiber. I believe Trefil Arbed was bought out by anoither company since, and I think the product is still around. However, this is probably way to specialized for what you're trying to do. I mention it mostly because steel fibers DO enhance bending strength, and it has been proven by testing.

 

[PicoStruc]

1) Question for spats

The fiber I talk about loollike hairpin for steel one and exploded fiber for plastic one.

What amount of bending resistance improvement does these fiber add ?

2)

Note to the original poster : Proven by testing is the key here. As generally prescribe by code, if you specify a different solution than the code requirements, you need to prove the solution by testing (or done by the fiber manifacturer !)

 

[spats]

I dug through my archives, and found the attached load tables, and forms to send to TrefilARBED (at the time) where they would evaluate your slab for you using their software. You can make your own determination as to how much bending is improved. From what I can remember, it wasn't just a matter of increased strength, but the fibers contol the cracking patterns and crack widths, and provide ductile behavior after failure of the concrete matrix. The fiber reinforcement allows plastic moment redistribution in the slab which also enhances load resistance.

The other significant enhancement is that we were able to construct the entire rocket assembly floor area without a single joint!