field bending of rebar

huangyhg

field bending of rebar
aci 318 states that field bending of rebar is not permitted unless approved by the engineer.  research has shown that (cold) field bending a bar less than a #7 usually doesn't have any negative effects to the integrity of the bar.  if there is no significant yielding, cracking, or, or kinking of the bar, i would expect that it's not a problem.  does anyone else have any thoughts or experience on this matter?
i have seen rebar bent in the field where an undersize dolly was used. the bar showed severe cracking. i would have thought that the requirement is partly to make sure that the minimum bending radius is maintained.
stephen argles
land & marine
32romeo, are you referring to aci 318 section 7.3.2, which deals with bending of bars partially embedded in concrete? if you are, there is pertinent commentary provided in r7.3.2.
yes, i was refering to aci 318-7.3.2.  i have researched this in several standards and know what they have to say...i just wanted to get some wisdom from the experienced engineers out there.  thanks for your input.
the problem with field bending of bars is that the minimum bending radius is not maintained.  the people bending these bars have no idea that a minimum bending radius requirement even exist.
vertical dowels at footings and horizontal dowels at wall construction joints are often bent over at 90 to facilitate foot and/or machine traffic.  "l" dowels at the tops of walls to catch intersecting slabs are often bent over at 90 to facilitate backfill placement.  never a good idea.
i would recommend field bending when you have small bars such as #5 or #6 embedded in concrete and i beleive that the aci code is favorable to this also.  
general field bending on all bars not embedded in concrete should be done with a proper mandrel and template which most rod-bende companies have even if they don't know it!
regards,
qshake
eng-tips forums:real solutions for real problems really quick.
one of the other problems with field bending is that the bars are many times bent down, and then subsequently bent back up - a double whammy on the bar material at the bend.
field bending of bars up to #6, by skilled steel workers, is a common practice at many countries, especially for small jobs and field changes. for bars above #6, the workers will have difficulties to handle it, and shall be avoided.
i always tell the contractor any bar he can bend around is head with his hands is ok to bend.  that usually ends the conversation.
field bending is a common practice and is used to accomadte work on the site. generally the designer does not take into account the work that is needed to install the conrete and the bars are bent to accomadate the work generally 6's and down are bent. 7's and up get tough. if designers don't want bars bent, they should consider common constrution methods in their design. most bars never get stressed to their design capacity, so it generally is not an issue.
wait until you find out what they bend with.  if the bar is already cast, such as a dowel, it won't get bent, it will get "persuaded".  a sledge hammer is pretty effective at bending bars, when you don't snap off because of it.  
of course the bars always yield when bent; they are undergoing significant plastic deformation.  i don't see any problem as long as you get the minimum radius.  there are bar bending tools that bend the bar over a cylinder that meets the minimum radius upto a given size bar.  the ones that pull the bar across a wheel as it is bent cause less strain in the bar.