180 vs 90 deg. Hooks in Pilecaps 2

[Lazzaroni]

Hello all.....Is there a reason CRSI uses 180 deg. hooks at the bottom of pilecaps? It states, "The provision to include a 180 deg. end hooks or heads on all reinforcing bars in pile caps with single lines of piles around the column is a prudent precaution against a premature "tied-arch" shear failure mode." ACI does not differentiate between 180 & 90 deg hooks.
Wouldn't a 90 deg hook perform the same function?

 

[TXStructural]

A 180 degree hook provides superior confinement of the hook extension (tail). 90 degree hooks are restrained only by the tensile capacity of the cover, and when heavily stressed, the confining cover may be broken away more readily by 90 degree hooks than 180 hooks. The allowance in ACI 318 12.5.3 for a reduction in Ldh with thick cover recognizes this. Also note that ACI 318 12.5.3 allows further reductions where there is significant confinement of 180 degree hooks.

In this application, the bar needs to be developed as close to the edge of the pile cap as possible, and from a practical perspective, 180 degree hooks are capable of developing the full bar capacity in a shorter distance.

John Turner CSP PE
CRSI Greater Southwestern Regional Manager

 

[Lazzaroni]

Thanks TX...good info.