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FRP reinforcement

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Prakash,

We looked at FRP rebar for a client in the Middle East and I would agree
with Rogers comments below and would add two more.  The stuff we looked at
had a very low modulus of elasticity compared to steel so deflection can be
a real problem for elevated structures.  The biggest problem we had however
was the construction/installation.  You can not field or shop bend FRP
rebar.  If all you have are straight bars in a slab then this is not much
of a problem but if you have a lot of bends or unique corner/angle details
then you have to either custom make the joint splices or try to be make
their pre-made 90 degree products work.  It requires a lot of splice
pieces.

Thomas Hunt, S.E.
Duke/Fluor Daniel

----- Forwarded by Tom Hunt/DFD on 05/21/01 03:51 PM -----
                                                                                                                       
                    Roger Turk                                                                                         
                    <73527.1356@compu        To:     seaint(--nospam--at)seaint.org                                                 
                    serve.com>               cc:                                                                       
                                             Subject:     FRP reinforcement                                            
                    05/21/01 11:22 AM                                                                                  
                    Please respond to                                                                                  
                    seaint                                                                                             
                                                                                                                       
                                                                                                                       




One of the problems that I see with FRP reinforcement is that the
stress-strain curve is like glass, i.e., linear until failure.  There is
*no*
ductility or yielding of the material.  To get the structure to deflect
like
a sway-back mule just before failure (as we engineers want structures to
do)
will require designing to a working stress significantly below failure,
possibly 0.2Fult.

Another problem that I see with FRP reinforcement is that the coefficient
of
thermal expansion in comparison to concrete has just about been ignored.
One of the reasons the marriage of steel and concrete has been successful
is
that their coefficients of thermal expansion were very close.

When I was a graduate student, Professor Jim Kreigh was doing research on
epoxies.  In order to justify my pay check one summer, I was given the job
of
reviewing thermal expansion tests on epoxy specimens.  As the temperature
increased, the epoxy specimen's length increased --- up to a certain point,
then suddenly shortened, only to resume the expansion and subsequent
shortening in a saw-tooth manner as the temperature continued to increase.
I
spoke to a neighbor about this who was doing post-graduate work in polymer
chemistry under Dr. Carl Marvel.  He took the problem to Dr. Marvel and
came
back with the explanation that the expansion/contraction was due to the
polymers unlinking when the temperature reached a certain level and then
relinking.  How this action affects the concrete/FRP reinforcing interface,
I
do not know.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Prakash C. Chowdhury wrote:

. > We (in India) read about FRP reinforcement in conference/seminar
. > literature but wonder what are the ground realities. Is this really the
. > way to go simply because of corrosion? Will this, or any other
non-ferrous
. > rebar, be economically viable even over stainless steel in the
foreseeable
. > future? It will be interesting to have subjective opinions from list
. > members as to its real prospects (in terms of tonnages or percents)
over
. > the next decade or two. This period, I think, fairly reflects the gap
. > between developed and developing countries for construction technology.
. > Though there are exceptions e.g. high-yield strength rebars, in the
form
. > of TOR cold-worked bars, were licenced by Tor-Isteg Steel Corporation
. > (Luxembourg) in India a few years before it replaced square-twisted
bars
. > in U.K.

. > I would also appreciate being directed to references/websites that give
. > the state of the art for engineering information about properties and
. > methods of manufacture. There was a book published in U.K. in the 90's
but
. > this must be a fast developing area.



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