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Re: RFP Reinforcing

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While I agree with much of what you said, I will take at least a very
small issue with the statement below.  I think that such a statement
should be qualified as such...

"USD for use with conventional reinforcing is based on the reinforcing
yielding, something..."

You are certainly correct the USD methodoloy for conventional reinforced
concrete is based upon the idea that the steel reinforcing will yield
before the concrete crushes.  I would offer, however, that there can still
be a "ultimate strength design" method created for use with FRP bars.  It
will obviously not work exactly like the method for conventional R/C.  To
me, the one of the primary philosophical differences between USD/LRFD and
WSD/ASD has been the "failure" point (from a structural point of view not
a lay point of view) used as the basis of establishing the factor of
safety and used in the calculations.  USD/LRFD is based off of a failure
load (i.e. the ultimate load...something that is fairly well defined in
structural engineering) rather than some imaginary "allowable load" that
is determined with some "bugger" factor.  While in theory, both should
come up with nominally the same design (in reality too since the
structure does not care at all that you designed it in LRFD/USD or
ASD/WSD), USD/LRFD is to me a more "rational" method, especially when
dealing with seismic related issues.

The end result is that it is certainly possible to develop a ultimate
strength method for R/C with FRP reinforcing.  This is entirely
independent of whether or not FRP reinforced concrete is a good thing or
not (considering the we as structural engineers tend to like materials
that will have some sort of ductile failure mechanish...i.e. we like that
sway-backed mule stuff).


Ypsilanti, MI

On Sat, 21 Jun 2003, Roger Turk wrote:

> 3. USD is based on the reinforcing yielding, something that FRP reinforcing
> does not do.

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