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FRP reinforcement

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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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