Bridge deck pour sequence

[Enginerdad]

For simple span bridges, the state DOT that I'm working for requires in their standard specifications that the deck concrete be placed from the expansion end of the bridge toward the fixed end. Can anyone think of why this may be? I know the reasons for deck sequencing in continuous multi-span structures, so that the negative monent zones are poured last, but I can't think of why which end you start at would matter in a simple span.

 

[BridgeSmith]

I would guess it's because they don't want the deflection of the girders (and the associated rotation at the abutment) to be pulling on the concrete between the abutment and the girders, inducing tension stresses in the concrete while the concrete is just starting to cure. The expansion joint end is (presumably) free to rotate independent of the abutment, but the fixed end is not.