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RE: Minimum Temperature Reinforcement

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Walter,

The thought by Joe Otto also came to my mind when I read your post --- Will 
the quality of construction be the same in the field as it was in the full 
scale models that you tested?

I would suggest that you research the basis for the minimum amount of 
reinforcing required by the code.  IIRC, tests performed in the early 1930's 
showed that long term creep and shrinkage placed an incredible strain on 
reinforcing, bringing it almost to yield.  These effects would not 
necessarily affect the results of short term testing but sure would have 
affect the performance of the structure ten or twenty years down the road.

For many years, the ACI Code had a requirement for minimum size and 
reinforcing of columns because of creep and shrinkage effects.  The minimum 
reinforcing was 6 #5 bars, and the minimum column area was 120 in^2; minimum 
diameter of round columns: 12"; minimum dimension of rectangular columns: 8", 
but posts not continuous from story to story could have a minimum dimension 
of 6".  Somehow these important requirements got dropped from the codes after 
USD became the dominate method of design.

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

Joe Otto wrote:

>>Walter,

I could be way off base; But, (IMHO) the following questions come to mind
when I consider this post.

A.      Are the walls which will become part of the structure also going to be
built in the laboratory by engineers or are they going to be built by the
lowest bidder who may not be able to achieve the same quality of wall in the
field as was achieved in the lab?

B.      Is it ethical to skimp on materials.  The recipients of these homes 
would probably be grateful for any king of housing. But, if you're going to do
them a favor, aren't you obligated to do them a favor.

Joseph M. Otto<<

and Walter Sheen wrote:

>>Dear Fellows:

We have been working developing a small house for poor people. This one is
made out of four inch reinforced concrete walls. We have been able to prove
that a 1400 psi concrete is enough for the expected lateral forces and also
for dead and live load. We have used the minimum specified steel
reinforcement for temperature and tested a natural scale module in a
laboratory. We have found that it resists 8 times the expected lateral
force. Now since we made the cement contents as low as we could, now we
want (if possible) to put less steel reinforcement. Now I'd like to ask:

1.- Temperatures between summer and winter have a 25 Celsius degrees, which
is not a lot. How is this minimum steel reinforcement determined ?
2.- In your opinion, for cracking control, would it be bad to use less
steel?
3.- We are planning to use welded wire reinforcement. If we specify small
distance between wires, would it be possible to use less amount of steel ?

Thanks for your help.




Walter E. Sheen<<