NU girders, debonding outside of top flange

[OSUCivlEng]

I was talking with a coworker in another office this morning. He is designing a new bridge with NU girders and was reviewing the state DOT's design requirements.

One of them was placing felt paper on the outside 9" of each side of the top flange.

This bridge is off system and tge DOT has no jurisdiction so he isn't going to follow it.

Anyone have any idea what purpose the debonding serves?

 

[Agent666]

Got a drawing or picture?

Trying to get slab reaction centrally over the web of the girder?

 

[BridgeSmith]

I would guess that the DOT has had issues with allowing the edges of the flange to bond with the slab. Perhaps the difference in the modulus of elasticity between the slab and girders is enough to cause spalling. I suggest contacting someone at the DOT familiar with the design of that type of bridge, and ask them. There are some things we do at the DOT just because 'we've always done it that way', but the NU girders are a fairly recent invention, so the detail is likely addressing an issue that's come up.

Rod Smith, P.E.

 

[wiktor]

The debonding is provided to facilitate for future deck replacement, allowing for quicker and easier deck removal. I'm attaching some more information which could be very useful.

 

[OSUCivlEng]

Replacing the deck on PC Beams is wrought with problems. Contractors I know say it's often cheaper to replace the beams due to the labor costs of a bunch of guys with "rivet busters" doing the final concrete removal around the shear connectors while trying to avoid damaging the beams.