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Re: RFP Reinforcing

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If stress is the limiting design factor, I cannot see complicating something 
or developing something new because of a current fad (LRFD).

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

Scott Maxwell wrote:

. > Roger,

. > 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).

. > HTH,

. > Scott
. > Ypsilanti, MI

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