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Re: RFP Reinforcing

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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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