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MechElement (Mechanical) (OP)
1 Jan 06 1:06
I've asked the 3 Civil engineers here at work and none of them know. There must be a general rule of thumb.

What is the minimum bending radius for rebar?

I have been under the impression from a civil designer, the minimum radius for rebar is three times the diameter of the rebar.

A civil (structural) engineer redesigned lifting eyes on top of T-walls which I designed and implemented over a year ago. He made the radius very small - the shape of the lifting eye was basically a square - and downsized the rebar. All of the lifting eyes failed on all of the T-walls as they were properly hoised. The lifting eyes failed at the newly designed bends. This has lead to 3 injuries. LUCKILY nobody was killed.

Helpful Member!  UcfSE (Structural)
1 Jan 06 1:48
Look at ACI 318-02 section 7.2.  Table 7.2 gives minimum bend diameter  based on bar diameter.  Basically it is:
3 through 8 use 6db
9, 10, 11 use 8db
14, 18 use 10db

where db is the bar diameter.  For stirrups and ties, 7.2.2 gives 4db as the minimum bend for bars sizes 5 and smaller.  

It would seem that the minimum no matter what is 4db and usually you are required to go to 6db or more.
henri2 (Materials)
1 Jan 06 10:45
Is rebar suitable for lifting eyes in this situation? Check PCI MNL 116 Manual for Quality Control For Plants and Production of Structural Precast Concrete Products, Article 3.2.4 (including commentary).

MechElement (Mechanical) (OP)
1 Jan 06 13:00
UcfSE, thank you for the helpful information. Unfortunately we don't have access to the ACI 318-02 reference.

henri2, we're in a warzone right now, so those nice lifting eyes are unavailable.

Thanks again.

kenvlach (Materials)
2 Jan 06 5:41
Perhaps use a stronger grade of rebar.  The ASTM rebar bend test requirements at any given size are the same for each grade  (although ductility, as measured by elongation in tensile test, decreases as strength increases).  Logically, the ASTM requirements for the steel are tighter (smaller bend diameters for a 180o bend) than the ACI-permitted usage.

ASTM A615 carbon-steel rebar grades, given in terms of minimum yield strengths:
Grade 40:  YS 40 ksi [280 Mpa], TS 60 ksi [420 Mpa]  furnished only in sizes 3-6 [10-19 mm],
Grade 60:  YS 60 [420], TS 90 ksi [620]  
Grade 75:  YS 75 [520], TS 100 ksi [690]  furnished only in sizes 6-18 [19-57].

ASTM A706 low-alloy rebar, only Grade 60: YS 60 ksi [420 Mpa], TS 80 ksi [550].

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