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Re: RFP Reinforcing

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Fellow engineers

        I have replied privately to Roger Turk's submission which is copied
below.  The text of my reply follows; the attachments are not included because
they would have made it too long for posting on this list.

Regards,

H. Daryl Richardson

Roger,

        I have scanned four pages, 20, 21, 26, and 27 from my ancient
textbook, "Reinforced Concrete Fundamentals" by Ferguson, published by
Wiley, copyright 1958, fourth printing 1961 as backup for my earlier
statement "The reason that USD was developed in the first place is that
the shrinkage and creep characteristics of concrete made the existing
composite section theory inaccurate and unreliable, particularly for
columns and for beams with compression reinforcement."

        In making the statement I seem to have implied that it was the
only reason for changing to USD; clearly it was not the only reason but
it was an important reason as implied in the discussions on pager 20,
26, and 27.  At lease some of the limitations of USD, as discussed on
page 21, (which generally centred on lack of knowledge of materials and
procedures) will have disappeared over the 45 years since this book was
written.

        Regarding the bamboo reinforcing, I suggested it because there
seemed to be some similarities between FRP and bamboo, namely lower
strength, lower E value, and little or no marked yielding.  It seemed to
me that at least some of the experience with bamboo reinforcing might be
transferable; and there must be either some literature or some people to
make this experience available.  I have not personally had any
experience or read any literature on the subject.

        By the way, I like your contributions to the list.  All of
them!  It's a pleasure to read good responses to some of the interesting
questions asked.

Best regards, Roger,

H. Daryl Richardson

Roger Turk wrote:

> Daryl Richardson wrote:
>
> . > The reason that USD was developed in the first place is that the
> . > shrinkage and creep characteristics of concrete made the existing
> . > composite section theory inaccurate and unreliable, particularly for
> . > columns and for beams with compression reinforcement.
>
> I can't say that I ever heard anything close to this explanation before, but
> that will be another discussion at another time.
>
> . > I don't completely agree with your suggestion that ASD be used,
> . > however.
>
> . > I agree completely with your recommendation to lower the stresses
> . > significantly.
>
> . >         There is another source of experience that may be worth
> . > accessing: in China, (and in other countries, I expect) I am reliably
> . > informed, they have actually used a lot of bamboo for concrete
> . > reinforcing. It might be worth trying to tap into some of their
> . > experience; some of it might be very transferable.
>
> In mulling over my response to Daryl's post, I realized that my suggestion
> that 50% of ultimate stress be the limiting stresses for FRP concrete design
> was much too high.  WSD concrete already limits/limited the allowable stress
> in concrete to .45fc' and .6fy for reinforcing steel and these values are
> based on ductile response of reinforcing.  I would therefor modify my
> previous suggestion that the limiting stresses for both the reinforcing and
> concrete in FRP concrete be not more than 25% of ultimate.
>
> The reason that I stated that ASD be used is because,
>
> 1. Limiting stresses are used, not ultimate capacity.
>
> 2. The stress-strain curve for concrete is essentially linear up to about 50%
> of its ultimate strength and lends itself to the simplicity of WSD.
>
> 3. USD is based on the reinforcing yielding, something that FRP reinforcing
> does not do.
>
> I am aware of the stories about bamboo having historically been used for
> reinforcing in China, and I believe that I saw at least one published paper
> in the last 10-20 years on contemporary bamboo reinforced concrete tests.
> The fact of the matter is that *any* material that is capable of taking
> tension can be used to substitute for concrete's inability to resist
> tension.  How predictable, compatible and durable the two materials are will
> be is another story.  In time of need, any material will do.  I recall beer
> can houses in Korea during the Korean war which served a function (shelter)
> in the absence of more appropriate alternatives.
>
> A. Roger Turk, P.E.(Structural)
> Tucson, Arizona
>
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