Differential Shrinkage for Bridges

[VoyageofDiscovery]

How do you account for differential shrinkage in composite bridge girders? The new Canadian Bridge Code requires this in a specific load combination to be checked. Is there an agreed upon method? Branson '64 compares two methods and reports increasing strains in different locations for shored and unshored construction through his testing. He finally recommends one, though it does not appear to be followed in the Canadian Bridge Code through its references, what about AASHTO or ACI? There is newer research here in Canada tending to use the Tensile Elastic Modulus of Concrete versus the Compressive Elastic Modulus of Concrete.

Anyone?

 

[wiktor]

I have not found many references on the above topic. In some of the projects done in the past,I have assumed that the differential shrinkage for the composite section would be equivalent to the temperature drop of 15 C, based on the DIN standard. That's seems to be excesive, and some evaluation is required, based on the type of concrete used, curing conditions, e.t.c.
To account for this, I have calculated the additional moment in the composite section caused by the shirnkage shortening of the deck. As the effect of the shrinkage is equivalent to the post-tensioning, same techniques could be used to evaluate the effect.