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abutment uplift

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Chris Towne wrote:

. > I take it that there are not that many bridge engineers on this list.

Oh, I wouldn't say that!

Like any other beam/girder that has uplift at a support, you have to tie it 
down.  The means of accomplishing this is as varied as twice the number of 
engineers that you talk to.

Typically, uplift at an abutment will occur only when you have a very short 
end span in a continuous structure.  For balancing of moments, the span 
ratios should be of the order of:

      .75L-1.0L-1.0L-....-1.0L-.75L

What I am trying to figure out is what is a, "semi-integral" abutment?

If you are considering using an integral abutment, the bridge should have 
*no* skew.  If there is skew, it should be recognized that the abutment will 
be very flexible perpendicular to the abutment and very stiff along the 
abutment.  Thermal movement of the deck will cause the abutment to try to 
move in a direction parallel to the girders, but the abutment will want to 
move perpendicular to the abutment, and has to be forced to move in a 
direction parallel to the girders.  Failing to consider this can result in 
distress in the abutment or in the deck (longitudinal cracking over the 
girders).

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