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Re: Steel Reinforcement Elongation Limit

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Jim,

If you can get some details on the composite material and the
steel/composite geometery you are proposing, I might be able to help. 
For FRP and similar composite materials, it is somewhat true the
material is "elastic until failure, with no plastic deformation." 
However, there is no hard and fast rule about how much the steel can
elongate safely since so much of the answer is "it depends."  I've run
across this in process equipment and related facility work, and have
seen failure where loads were well below yield yet either the composite
failed or the bond failed due to composite internal structure, localized
stresses/deformations, or significant differences in the rate of
elongation for a given load.  There aren't any easy "cookbook" codes on
the matter precisely because of the variables and continual changes in
technology involved.  

Clear as mud?  Short answer: as long as the steel doesn't elongate and
everything is below yield, there is no problem.  Usually.  If the steel
does flex or otherwise deform where the composite bonds with the
steel......it depends.  You can email me offlist (bkemper(--nospam--at)bigdogz.com)
if you'd like.

Bart Kemper, P.E.

Scott E Maxwell wrote:
> 
> Now that you supply additional relevant information, I can better
> understand your question.  Unfortunately, I will not be much help.  I
> haven't had the privaledge of working with some of the more advanced
> materials.
> 
> I assume when you say composites, you are referring to FRP.  If so there
> was an article in the Feb. 2000 issue of Structural Engineer magazine
> about using FRP to reinforce existing concrete members.  The article
> outlined a method for determining the design.  While you may not want to
> use their method (I have real knowledge in this area, so I don't know how
> useful it is), you could contact the authors for information.  The authors
> were William Gold and Gregg Blaszak.  They might be able to provide the
> answers to your questions.  I am sure that you could get in contact with
> them through the magazine (their company was not listed).
> 
> Hope this helps,
> 
> Scott Maxwell, PE, SE
> 
> On Tue, 25 Jul 2000, frp 2000 wrote:
> 
> > This is true....
> >
> > I am however trying to determine what would be an appropriate limiting
> > elongation when applying composite plates to the underside of beams for
> > flexural strengthening.
> >
> > Composites have no plasticity...they are elastic to failure....
> >
> > Plates can be manufactured to have the same modulus as steel (oops...is that
> > 29ksi or 30ksi ?).....However, they are elastic up to failure, so it would
> > be nice to have an understanding of the maximum elongation that will keep
> > the underlying concrete from separating from the existing steel
> > rebars....precisely to avoid catastrophic failures..
> >
> >
> > jim
> >
> >
> > ----- Original Message -----
> > From: "Scott E Maxwell" <smaxwell(--nospam--at)engin.umich.edu>
> > To: <seaint(--nospam--at)seaint.org>
> > Sent: Tuesday, July 25, 2000 8:28 PM
> > Subject: Re: Steel Reinforcement Elongation Limit
> >
> >
> > > As well, I believe the intent of the ACI code is that the development
> > > length provided in the code would fully develop the bar.  This would mean
> > > that the bar would reach yield stregth and "plateau" while elongating.
> > > That is to say that no matter the elongation, the "bond" between the steel
> > > and concrete would never "break" allowing the bar to pull loose.  Thus,
> > > the bar would either fracture or the concrete would crush before the bar
> > > would pull loose.  This is all predicated on proper developement of the
> > > bar.
> > >
> > > I could be wrong, so maybe someone more knowledgeable will chime in...
> > >
> > > Scott Maxwell, PE, SE
> > >
> > >
> > > On Tue, 25 Jul 2000, Roger Turk wrote:
> > >
> > > > ASTM requires 11 to 12 percent (min.) for Grade 40 steel, and 7 to 9
> > percent
> > > > for Grade 60 steel.
> > > >
> > > > Since this is much beyond the cracking strain of concrete, the concrete
> > will
> > > > crack and go along for the ride.  (Take a piece of paper and cut one
> > edge in
> > > > parallel strips and glue a rubber band across the strips.  Pull the
> > rubber
> > > > band and see if the glue comes loose.)
> > > >
> > > > At these strains, deflected shape becomes a part in determining the
> > capacity
> > > > of the structure with the structure behaving like a cable supported
> > structure
> > > > more than a flexural member.
> > > >
> > > > We (at least *I* do) want our structures to look like a sway-backed mule
> > > > before it collapses.  I do not want strains limited so that collapse
> > comes
> > > > suddenly and without warning.!
> > > >
> > > > A. Roger Turk, P.E.(Structural)
> > > > Tucson, Arizona
> > > >
> > > > Jim Korff wrote:
> > > >
> > > > >>The steel reinforcement "yield point" is at an elongation of .002
> > (0.2%)
> > > >
> > > > Does ACI Code give a maximum permitted elongation for internal
> > reinforcement
> > > > ??
> > > >
> > > > (For DIN it is 0.5% and for the Euro Standard it is 1.0% )
> > > >
> > > > Are there any papers or research on this subject -maximum elongation to
> > > > avoid steel/concrete bond failure ??<<
> > > >

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