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Skewed bridge deck reinforcing

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Tripp,
you wrote:
>We are designing a concrete highway bridge.  The
>support bents for the bridge are at a 26-degree skew
>to the AASHTO girders, which run parallel with the
>length of the bridge.  A control joint has to be
>installed above each support bent.  The girder span
>and width of the bridge works out in such a way that
>if the main deck reinforcing is installed
>perpendicular to the AASHTO girders, as is normally
>done, each piece would have to be detailed and cut to
>a different length.  This would not only make our job
>tougher but the poor contractor's as well.

>We would like to skew the main deck reinforcing to be
>parallel with the support bents so that they can all
>be the same length.  The question is just how do we
>size the reinforcing since it is at a skew to the
>actual direction of bending?  

Your methodology is correct: divide the area by the
cosine of the skew.  But a few comments and questions:

Who are you designing the bridge for?  It doesn't
sound like a private-dollars, do-whatever-you-want
kind of bridge.  Most DOT's (at least around here)
have published rules regarding such details.  Most of
them switch from skewed transverse reinforcing to
normal (90 degree) reinforcing with variable cutoffs,
somewhere between 15 and 20 degrees of skew.  The
variable length bars aren't looked upon as that big a
deal.

As far as that goes, most of the DOT's have published
tables of deck reinforcing too.  Are you actually
designing the deck reinforcing?  Are you deciding how
thick to make the deck, and what the concrete mix
design and strength should be?  In this part of the
country, any bridge with public money of any kind is
designed to that state's DOT requirements and
standards; I've never actually designed a deck.

And yes, don't forget to put extra bars in the acute
corners where they overhang the beams.

Mike Hemstad, P.E.
TKDA
St. Paul, Minnesota


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