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RE: Bending Embedded Reinforcing Steel

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I have seen some Gawd-awful field bends and will prohibit rebending of 
reinforcing in the field.

While the requirements that would permit field bending require that the 
reinforcing be bent around the same diameter pin as is it would be in the 
field, that is rarely done.  And rarely is there enough room to get the 
proper diameter pin between the top of pour and where the horizontal leg 
needs to be.  Straightening of bent bars (for forming convenience) will 
result in the bar looking thusly:

   |
   |
   |
    \
     |
     |

If they are not straightened, then they are twisted and if the bond is not 
broken, the bar is torqued beyond its shear (diagonal tension) yield point.  
Then the bar is re-twisted again to bring it back to, or near, its original 
position.  Some bars are straightened and twisted at the same time and lord 
knows what condition they are in after that.

The research that was done indicating that one reversing field bend is 
satisfactory was done under laboratory conditions, which do not come close to 
field conditions.

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

Bill Cain wrote:

Thor-
Doesn't the shop bend in the Z count as one?  Would not the field bend then
be the second bend at the "same" location?  I concur with Fountain.
Regards,
Bill Cain, S.E.
Oakland CA

-----Original Message-----
From: vicpeng [mailto:vicpeng(--nospam--at)sprint.ca]
Sent: Saturday, July 07, 2001 11:34 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Bending Embedded Reinforcing Steel


I interpreted the report to mean a second, third, etc bend at the same
location.  I'll try to find it and sent it to you.  Shall I post it to the
list?

Thor A Tandy P.Eng
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)sprint.ca <mailto:vicpeng(--nospam--at)sprint.ca> 

----- Original Message ----- 
From: Fountain Conner <mailto:fconner(--nospam--at)pcola.gulf.net>  
To: seaint(--nospam--at)seaint.org <mailto:seaint(--nospam--at)seaint.org>  
Sent: Saturday, July 07, 2001 10:56 AM
Subject: Re: Bending Embedded Reinforcing Steel

I'm not familiar with the report, but...

If it's correct the magic "one" bend would occur when the shop made the "Z"
bend.  Straightening the bar in the field would be the second bend.

After all these years, I can count to two.

Fountain

----------
From: vicpeng < vicpeng(--nospam--at)sprint.ca <mailto:vicpeng(--nospam--at)sprint.ca> >
To: seaint(--nospam--at)seaint.org <mailto:seaint(--nospam--at)seaint.org> 
Subject: Re: Bending Embedded Reinforcing Steel
Date: Saturday, July 07, 2001 12:14 PM

There was report issued about 11 years ago in New Zealand following some
research on the bending of rebar.  It found that one (1) cold bend of rebar
resulted in minimal loss of strength, however, on two (2) or bends there
was a drastic loss of strength.  I therefore only allow one cold bend,
however, what I don't see ....  Heating and bending is definitely out!

Hence you need to exercise caution with on-site bending.

Thor A Tandy P.Eng
Victoria BC
Canada
e-mail: vicpeng(--nospam--at)sprint.ca <mailto:vicpeng(--nospam--at)sprint.ca> 
  ----- Original Message ----- 
  From: Jim Persing 
  To: SEAINT 
  Sent: Friday, July 06, 2001 11:30 PM
  Subject: Bending Embedded Reinforcing Steel


  I have a detail on my plans with #4 bars bent 90 degrees from vertical in
a
  concrete stem wall to horizontal into a slab on grade.  Nothing unusual.
  The contractor wants to install embedded bars in the stem wall with the
90
  degree bend to horizontal and then another 90 degree bend back to the
  vertical just outside of the stem wall to make kind of a vertical Zee. 
This
  last bend is temporary and will be bent back to horizontal when the slab
is
  placed.    I have an older CRSI book which allows it only with the
approval
  of the engineer and also a CRSI Engineering Data Report Number 12 which
  seems to indicate that it is probably OK for smaller bars.

  I can think of lots of reasons why this should not be done but just
wonder
  if anyone else has had this detail presented to them and whether or not
they
  approved it and why.

  Thanks,
  Jim Persing, SE
  Advanced Structural Concepts
  Bellevue, WA

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