REBAR HOOK BEND RADIUS

[JD2]

I AM WORKING ON A JOB NOW WHERE SEVERAL CONCRETE COLUMNS HAVE ALREADY BEEN POURED AND IT WAS DETERMINED, AFTER THE FACT, THAT HOOKS (IN THE FOOTINGS) ON DOWELS COMING OUT OF THE FOOTING INTO THE COLUMN FOR SOME OF THE BAR TYPES (#7 AND #9 BARS) DO NOT MEET THE MINIMUM BENDING RADIUS REQUIREMENTS FOR A STANDARD ACI HOOK (THE HOOK EXTENSION IS ADEQUATE). IT WAS FIRST NOTICED WHEN A HOOK ON ONE OF THE BARS WAS DISCOVERED TO HAVE A CRACK APPROXIMATELY 3/4'S THE WIDTH OF THE BAR AND APPROXIMATELY 3/16" DEEP. I KNOW THAT THE BEND RADIUS FOR THE STANDARD ACI HOOK IS DESIGNED TO MINIMIZE THE STRESS IN THE BAR DUE TO THE BENDING PROCESS AND PREVENT SPLITTING OR FAILURE OF THE BAR AT THE HOOK. I HAVE NOT GONE BACK TO DETERMINE IF THE HOOKS ARE ACTUALLY REQUIRED IN THE BARS OF THESE PARTICULAR COLUMNS TO DEVELOPE THE REQUIRED FORCES SO MY QUESTIONS AT THIS POINT ARE SOMEWHAT ACADEMIC - FOR MY INFORMATION. IF BARS TERMINATING IN HOOKS HAVE BEEN BENT AND DO NOT SHOW SIGNS OF SPLITTING OR CRACKING AT THE BEND OF THE HOOK, CAN THE HOOK STILL BE COUNTED ON AS BEING EFFECTIVE? DOES IT DEPEND ON THE ACTUAL RADIUS OF THE BEND? IS THERE ANYTHING IN THE RESEARCH LITERATURE THAT CAN BE REFERENCED? ANY INFORMATION WOULD BE GREATLY APPRECIATED.

 

[kenvlach]

I am not qualified to answer ACI code questions, but know rather a lot about steels.
Since some bent bars have visible cracks, I would warn that other bars in a similar configuration are likely to be on the verge of cracking. These are surely beyond design limits, and I cannot believe that any code would permit their use.

Is the rebar steel per ASTM A615 or A617?

Repairs may entail properly bending some bars and then embedding them into the footing, perhaps by drilling and grouting or by exposing existing hooks back to a straight portion for welding. Again, these are just some ideas of a metallurgist; I don’t know what repairs are allowed by ACI code.

 

[RiBeneke]

There are pro's and con's :
The rebars embedded in the column bases are required to transmit tension and compression forces into the concrete of the base. The highest stress point is probably at the level of the top of the base. The section of bar below this point will have a reducing stress as the force in the bar is transmitted into the mass of concrete via the surface bond between the bar and the concrete. See ACI re bond stresses.
Therefore the force in the bar at the bend is likely to be lower and the unfractured remaining section of steel (if you know the amount) may be able to carry the load.
If the column structure will be subject to dynamic loads (machinery or vehicles on a bridge) then there is a risk of the cracks growing through the bar cross section and you should not try to use my reasoning above.
If the structure is intended to resist earthquake or ductile failure, then also cracked bars will not be allowed.

 

[sdz]

If the bars carry only compression load there should be no problem because the bend is only there to facilitate fixing. Hooks and cogs don't count for compression development length; at least under the Australian code.

If in tension it could be another matter.