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RE: Re: Minimum steel in slabs on ground==>>FRC is a great invention/discovery of the 20th Century!!

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Jordan,

While much of what you say is true, I will respond that fiber concrete
does have some advanages.  Like all materials, it just must be used
properly.

If nothing else, fiber concrete has a more ductile behaviour than plain
old concrete.  As "proof" have a cylinder test done on plain concrete vs.
one done with fibers in the concrete.  The decending leg of the
compression test will actually be present for the cylinder with the fibers
as the fibers will help the concrete achieve some confinment ability.

In addition, concrete with fibers can potentially be useful in seismic
uses as it helps increase the energy "absorption" characteristics of
concrete (i.e. ductility again).

But, it is important to note that it does require thoughtful, intelligent
use.  I will note that fibers are not in ACI 318 because they have really
yet to be proven (to the 318 committee at least) that they can be used in
place of traditional reinforcement for structural applications.  But, I
know that there has been interesting research done on using fiber concrete
in joints (in addition to rebar) that helped the connection perform in a
much more ductile manner for load reversals (i.e. seismic loading).  I
also know of research to use fiber concrete in "moment" style connections
for precast concrete (again in addition to rebars).

And I will note that most research that I am aware of use much higher
fiber contents than what you commonly see recommended by manufactures.  I
don't recall ever seeing any research that uses poly fibers as such low
dosages that you will see typically recommended for SOGs.

So, to me, fibers can be used, but still require the engineer to actually
learn about them and use their brain when they decided to use them
(imagine that).

Regards,

Scott
Adrian, MI


On Thu, 21 Oct 2004, Jordan Truesdell, PE wrote:

> I'm going take this one.  First, this is not directed at any professors
> who have worked in the industry, started a practice from scratch, and
> built their own firm into a profitable operation.  I don't know too many
> of those guys. It's also not directed specifically at Fyed, he just
> happens to be the one to have brought it up.
>
> In my experience, professors spend very little time designing and
> detailing production work and dealing with on-site problems, standard
> practices, change orders, and *gasp* client budget constraints.  This is
> particularly true of those who never see the outside of a classroom on
> their way to a PhD and an associate professorship.  There are few jobs as
> comfortable as a professor. I know, I have relatives who are professors.
> I also have worked in the Federal Government right out of college and
> know all about job security and benefits of a tenured position in a large
> institution. Show me several million square feet with a 20 year
> successful design history as EOR and we'll talk.
>
> As wonderful as some of these new materials are in a laboratory setting,
> there are far too many variables and far too few in-place installations
> to give them to a marketing group and tell them to make money.  Specs get
> hyped (never cut another control joint again!), dosages get cut (my local
> ready-mix's "standard" fiber add is half the producer's recommended), and
> errors occur on a daily basis.   It's one thing to have a bunch of grad
> students out there with calipers running a test. It's an entirely
> different matter to have a crew of twenty laborers, six of which don't
> speak the same language as the foreman, and four or five of them so
> hungover they might puke in the concrete mix if they smell one more bacon
> and sausage biscuit from Hardee's.
>
> Here's another suggestion: if your item of choice is so fantastic, make a
> generic version and get it into the code books with specs to match.  I
> don't want a four page glossy on your uber-idea, I want a section in the
> ACI or AISC code books that say "you can replace your standard <blah>
> with our uber<blah> one for one."  I want a document saying that if I use
> your product you've so carefully designed, that any dimwit can put it in,
> and if it breaks your lawyers will tell the client that I did the right
> thing, and you'll be footing the entire bill.
>
> I think that's it. Oh, except I'll want it to be 20% cheaper to install,
> so that when the contractor marks up his fee to account for the
> additional headaches of using a new material, and I add my extra hours of
> fee in for research and learning curve on your idea, it will still save
> the client a percent or two over the tried-and-true methods used for the
> last fifty years.
>
>
> At 11:13 AM 10/21/2004 +0300, Syed Fiaz wrote:
>       Gail:
>
>       I think you're being a little bit unfair to the learned
>       professors, especially to those who have contributions
>       towards research on "fiber-reinforced concrete".
>
>
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