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Torsion Reinforcing Question

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Even though it starts out sounding like it, this is not just for the bridge
folks .....

I'm reviewing a contractor's proposed modification (prepared by and signed
and sealed by a properly licensed professional engineer) to an intermediate
bent for a AASHTO girder bridge.  The modifications are needed because one
of the piles was driven out of tolerance about 6" transversely to the bent.

The offset creates torsion in the bent cap and additional moment in the
pile, but it is the torsion I have a question about.

As originally designed, the bent cap was 48" wide and double shear stirrups
were detailed.  The closed stirrups were 34" wide, so that each pair has 4
"legs":  one stirrup has a leg 3" clear of one face and another leg 7" clear
of the other face.  The companion stirrup is a mirror image.

The contractor proposed to widen the cap 4" to accommodate the
out-of-tolerance pile and wants to "spread" the existing stirrups to avoid
having to fabricate new stirrups.  I plan on rejecting the re-use of these
stirrups since they have 90 degree stirrup hooks rather than 135 degree
stirrup hooks and therefore cannot be considered effective for torsion.

However, my main question is this:  Do stirrups used for torsion have to be
closed perimeter stirrups?   Are paired stirrups (similar to what was
originally designed) acceptable?  If so, it seems that there would have to
be some minimum overlap distance required.

ACI 318-95 R11.6.4.1 discusses stirrups with lap splices, but this is really
a different case.


David Finley, P.E.