Minimum Temperature to Bend Rebar

[ForrestLowell]

Is there a minimum temperature to bend rebar? We have a legit bar bending operation at our construction site so I am not worried about bend radius and the like as we have machines that govern all that. But there was a question thrown out if there was a minimum ambient temperature to perform the bending. Section 7.3 of ACI 318 talks about heating the bar to bend to avoid cracks, but nothing about a minimum temperature. We will of course inspect the bar for cracks after we bend, but would like some input on if any knows of another code that would govern the min temp for bending operations. Thanks - Forrest

 

[TehMightyEngineer]

Not an answer to your question but if it's cold enough you're worried about bar bending causing cracking then I'm sure your workers are miserable, miserable workers are prone to make mistakes. How hard is it to put your rebar fab people in a temporary enclosure with a kerosene heater?

Have you checked ACI 306 regarding cold weather concreting?

Ian Riley, PE, SE
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[dik]

I remember way back (40+ years) and 60 grade stirrups were spec'd... it was cold and in winter and I accidentally dropped one of the stirrups on a concrete surface, and, it broke.

Dik

 

[TXStructural]

CRSI has looked at this in the past but since I am no longer there I cannot comment on their current recommendations. Check the tech notes available on crsi.org
That said, some bar may be brittle at temps below about 32F while some may be ductile below that temp. I would expect A706 and dual-spec (A615/A706) bars to be ductile at colder temps.
Many shops bend outdoors year round, with bars well below freezing. Others maintain slightly warmer temps to reduce brittleness and operator comfort/safety. In the field, ACI 301-16 3.3.2.8(a) requires partially-embedded bars to be warmer than 32F because of the experience of some in the industry.

 

[Agent666]

You are specifically looking for the ductile to brittle transition temperature.

I would assume there is research similar to the linked report below within your industry/country based on bars manufactured to your reinforcement standard (some minimum requirements might be located in this standard).
Link