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RE: Steel Fibers Replacing Structural Reinforcing?

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Professor Bayasi in San Diego State University has done lots of research about SFRC (Steel Fiber Reinforced Concrete) and has valuable publications for that.
 
as far as design, it is really simple. (like a rectangular section of concrete with tensile capacity bellow N.A and compression at top)
tensile strength value you can get is a function of the type of fiber you use (length and shape of fiber are really important) 
 
In general:
the common percentage of fiber is btwn .5% to 2% and what they are providing in your case is about 1.5% (which is in range)
it improves impact ,toughness,tensile strength,cracking behavior and shear resistance of concrete. (advantages)
needing more cement in mix (more shrinkage), being usually more expensive (for equivalent design), and its workability are the major disadvantages of that.
my main concern in your case is adequacy of using only fiber instead of #7 @12. based on my rough calc I get half of moment strength. so I think their design should be something like 1.5% fiber in addition to #7 @24"o/c (or equivalent)
 
other concern would be where you have top reinforcing. because if you use SFRC, after you pour concrete most of fibers go to the bot of slab and you will get more tensile strength at bot. So I would probably like to keep up to 70% of top reinforcements.
 
AM
 
-----Original Message-----
From: Meyer, Jonathan [mailto:jmeyer(--nospam--at)webbersmith.com]
Sent: Thursday, June 17, 2004 3:52 AM
To: seaint(--nospam--at)seaint.org
Subject: Steel Fibers Replacing Structural Reinforcing?

I am currently designing an industrial facility a portion of which is a rack supported building. We designed the mat foundation to support this building and came up with an 18 thick slab with two layers of #7 bars @12 OCEW. One of the concrete contractors has asked a steel fiber manufacturer to value engineer the reinforcing to determine if they can do it with steel fibers instead of the reinforcing specified. There are also slab on grade and elevated composite slabs in this facility. Thats the background, here is my question Has anyone replaced structural reinforcing with steel fibers and are there any standards related to such a replacement?

The steel fiber representative called me and told me that they would have to increase the slab thickness to 19 and use 60# of fiber per cubic yard. He invited me to use their software to verify the design. I guess I am a bit skeptical about using someone elses software that has a vested interest in the outcome of the design to produce a design. I told the steel fiber manufacturer that they would have to take full responsibility for the design and produce sealed stamped plans if they wanted to change my designs to steel fiber for the mat slab of the rack supported building. As far as the slabs on grade are concerned, I feel that if the client wants to use steel fibers in those areas that would be fine as long as they understand any limitations of the fibers.

Any input would be greatly appreciated. Thanks for you assistance.

Jonathan Meyer

Webber Smith Associates