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RE: Bridge Expansion Joint Elimination

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Tony Powers wrote:

. > I have also seen abutment joints removed from bridges by casting a 
. > concrete end diaphragm to encase the girder ends. 

The philosophy behind integral abutment bridges is that the abutment supports 
are flexible and will permit the abutment to move as expansion and 
contraction of the bridge occurs.  When this assumption (flexible abutments) 
is valid, it will only "work" for a bridge without a skew.  If the abutment 
is skewed, is only flexible in a direction normal to the axis of the 
abutment, and is very rigid in the direction of the abutment axis.  As a 
result, when there is expansion and contraction of the bridge deck, large 
horizontal shears (even with small skews) have to be developed in the bridge 
deck in order to force the abutment to move in the direction that the deck 
expands and contracts.  These large forces even occur in simply supported 
bridges with skewed piers.

Integral abutments do not eliminate the expansion joint, but just relocate it 
to the joint between the approach slab and the abutment.

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