bending of #7 bars 1

[chopscpb]

As far as i can see, if a number 7 rebar is to be bent in the field, it shall be bent using heat. What happens if a # 7 rebar is bent without heat? (note it was only bent once and still needs to be bent back in place)

 

[ToadJones]

It was accidentally bent in the field?

 

[chopscpb]

No, it was purposly bent to a 90 degree hook. CTR needed to but a bridge over monoilith. No requirements were followed, just bent.

 

[ToadJones]

Im confused as to what you are asking then?

 

[chopscpb]

The contractor should of used heat to bend these bars, he didnt, i want to know what problems can be attributed to cold bending a bar when it should of been heated.

 

[ToadJones]

No problem at all
ACI 7.3.1- All reinforcement shall be bent cold, unless otherwise permitted by the engineer

for a no. 7, the minimum bend diameter is 6 bar diameters

 

[jenofstructures]

why not use a much lower bar?

is it more time consuming? and not much economical since it needs a heating process and labor attention?



Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds

 

[hokie66]

How did they bend a #7 bar in the field? No mean feat.

 

[TXStructural]

The practical problems with bending a partially embedded bar are:
1) Does the bend conform to CRSI/ACI bend radius requirements? If the bend is tighter than permitted, there is a risk that the strength and integrity of the bar has been compromised.
2) Was there any bend at the face of concrete (there always is) which is tighter than a bend of proper radius? If so, there may be cause for concern of fracture when loaded.
3) How the heck do you properly field bend a #7 without using a hydraulic device? A pipe over the end of the bar IS NOT adequate to get the right shape.

The reason for heating to make the bend is to avoid cold-working the bar excessively, to avoid cracking or fracturing the bar, and to avoid making poorly-shaped bends which will not function properly when loaded to capacity.

 

[ToadJones]

We bend all of our own bars "in the field". We have a rebar bender. Its not all that big of a machine either. I was assuming that is what the OP was implying. Not just cranking the bar over a truck bumper.

 

[racookpe1978]

If I read the OP correctly, this single rebar was supposed to be installed "straight" at this particular location, but the contractor (in the field) cold bent it to a 90 degree hook.

Question is, or was, since it was bent once cold, can it be bent (again) back to the original shape?

My very strong recommendation, after bending many pieces of (albeit slightly smaller and thinner 1x1 and 1/2 x 1-1/4 square and rectangular steel pieces for curved stairs and ballesters)curved steel in the field, is to hot bend the nbr 7 bar back to shape.

A round bar that thick can be cold bent, but you need to very closely clamp the (correctly-shaped) straight length of bar, the hook (backwards!) and the bent tangent length. Than you have to anchor everything except your lever arm VERY firmly, find a place to "push" from, and get the bending arm exactly in plane with the current (and the furture) position of the bend. Once bending starts, then you have to "nest" or support the original straight length (the part between the concrete and the bend) correctly so IT doesn't bend at the concrete: otherwise, you've just put two (or more) new bends in the bar you're trying to get once straight length out of.

Far easier to torch heat the bend to a low red-orange, and use the heat to let you use a hundreds-times-less force at the single place where you want the bend. Also, no other part of the bar will want to bend other than the single place where you have torch-heated the bend.place where