M. David Finley, P.E.
Lake City, FL 32025
----- Original Message -----
Sent: Thursday, December 06, 2001 6:09
Subject: Skewed Bridge Deck
I'm sorry, I know this is going to be difficult to describe without a
diagram, but bear with me. 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?
Our current reasoning is as follows:
- Calculate the tension force required to resist the bending moment based
on the deck spanning 5-ft perp. to the AASHTO girders (which is in fact what
- Draw a force triangle with the hypoteneuse at 26-degrees and parallel to
the support bents and the skewed main deck reinforcing, and the horizontal
perp. to the AASHTO girders
- The tension force required would be proportional to the horizontal leg
of this triangle
- The actual force felt by the bars would be proportional to the ratio of
the hypoteneuse over the horizontal of this triangle
- To get the actual area of skewed reinforcing required, multiply the area
calculated in step (1) by the ration in step (4)
Does this make sense to anyone, or am I off my rocker? Any comments
would be greatly appreciated, especially if you've encountered this situation
Thanks for the help
Tripp Howard, EIT
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