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Re: Fracture in concrete

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Yep, the magic bullet against brittle behaviour in concrete is the
reinforcement.  Just plain ol' concrete is a brittle material.

Keep in mind, however, that reinforced concrete can still behave in a
brittle fashion if not designed properly.  A reinforced concrete beam for
example is designed so that the reinforcing steel will yield in tension
before the concrete will crush in compression.  If it were the other ways
around, then the failure would be in an unexpected, brittle manner.  Thus,
in the ACI 318 code there is an upper limit to the amount of reinforcement
that can be used in both flexural and compression members.

HTH,

Scott
Ypsilanti, MI


On Tue, 26 Nov 2002, Christopher Wright wrote:

> >In reinforced concrete (not talking prestressed at the moment), concrete
> >is ALWAYS considered cracked for strength design.
> That's the way I learned about it. You figure the moment of inertia based
> only on the portion of concrete which carries compression. Equivalent
> sections and all that. From your note I gather that the magic bullet
> against brittle behavior is incorporating reinforcing or prestressing to
> carry loading that would otherwise be applied as tension in concrete.
> Without tension there's no brittle fracture. More accurately if you can
> insure that a crack won't open under service loading you won't get the
> kind of brittle behavior described by linear elastic fracture mechanics.
> In effect it seems like the built-in compression helps prevent cracking
> (surface cracking, at least, which is the most severe) with tempered
> glass and shot peening metals.
>
> Much obliged for your guidance. You're right--I've never gotten into
> concrete. I guess it shows.
>
> Christopher Wright P.E.    |"They couldn't hit an elephant at
> chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
> ___________________________| John Sedgwick, Spotsylvania 1864)
> http://www.skypoint.com/~chrisw
>
>
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