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RE: FRP rebar in concrete design

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In January of last year I attended at short course called "Design and
Retrofit of Structures with Fiber Composites."  This course was part of the
Second International Conference on Composites in Infrastructure (ICCI '98)
and was put on by the University of Arizona and the National Science
Foundation.  The conference chariman was Hamid Saadatmanesh of the
University of Arizona (tel 520-621-2148.)  They had listed an internet
address at that time of http://engr.arizona.edu/~ICCI.  (I'm not sure if is
still valid.)  There was a rather larger binder of course notes and examples
that were given out as part of the course.

Glass rebar is an interesting material.  As Roger Turk pointed out, it does
not have the same coefficient of thermal expansion as steel.  In addition,
it has a relatively low resistance to moisture, is sensitive to alkaline
environments, and is easily damaged in handling.  Its elastic modulus is
less than half that of steel (if I remember correctly), and it exhibits the
scary phenomen of creep failure.  In other words, if the stress in the glass
fibers is maintained above some minimum value indefinitely, the glass will
rupture, even though the original stress was less than ultimate.  The
ultimate elongation of glass is greater than steel.  Therefore, deflections
will be greater for a glass rebar reinforced beam than for a steel
reinforced beam (due to lower modulus), but the beam will also be able to
take more deflection.  Ductility is not inherent, but they say you should be
able to see noticeable deflection before ultimate failure.  Bond failure of
composite rebar is through the deformation in the material, not in the
concrete.  Since different rebar manufacturers have different deformation
patterns, bond characteristics vary (ouch.)  It sounds like there's a good
deal of things to consider when designing with glass rebar.  However, I
talked to two gentlemen from Saudi Arabia who use glass rebar in concrete
buildings fairly regularly due to corrosion resistance.  Is there any
personal experience out there?

Mark H. Larsen, P.E.
Phoenix, Arizona