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Skewed Bridge Deck Reinforcing

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Your reasoning is correct.

The slab is, of course, going to span perpendicular to the girders.  What I 
do in cases like yours is to calculate the area required to span the 
perpendicular direction and then divide it by the cosine of the skew.  I then 
provide that area parallel to the skew.

It gets really interesting when you have a heavily skewed bridge on a curve, 
grade and superelevated.

BTW, don't forget top bars at the corners of the slab parallel to a line 
bisecting the angle.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Tripp Howard wrote:

. > 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 it does) 
. >    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 before.

. > Thanks for the help

. > Tripp Howard, EIT

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