Slab Offset ("A" Dimension, AKA "X" Dimension)

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Visa Ronanki
Slab Offset ("A" Dimension, AKA "X" Dimension)

The help file for PGSuper does a very good job of explaining the various effects that need to considered in a rigorous analysis of the slab haunch. One of these effects is as follows

"Deflection due to placement of superimposed dead loads on composite section"

But after composite section has been achieved any load placed on the deck will make the girder and deck deflect together and should not be influencing the "A" dimension calculation?

Am I misinterpreting the statement from help file?

Thanks in advance :)

jruby411
Slab Offset ("A" Dimension, AKA "X" Dimension)

I believe that if the superimposed load will cause a permanent deflection, and you want a "flat" final profile by adjusting the "A" dimension, then yes, additional superimposed DL will affect the "A" dimension.

Visa Ronanki
For a case when the

For a case when the Superimposed dead load is applied before the the slab achieves composite action What you are saying is true.
But once composite section has been achieved "A" dimension will not change. The girder and slab will deflect together

Rick Brice
What jruby411 is saying is

What jruby411 is saying is correct. The SIDL will cause permanent deflection so you have to build up the haunch a little extra so that after the SIDL is applied, the deck will be at the desired elevation.

This is consistent with the information provided in the new bridge geometry manual from PCI.

Visa Ronanki
Thank you for clarifying. I

Thank you for clarifying. I was previously approaching this from the point of view that; the only criteria for "A" dimension design is to not allow the girder to camber up into the slab thickness, hence the confusion.

If achieving a desired bridge deck elevation after all SIDL is applied is also a criteria, then yes this deflection has to be included and the "A" dimension could be increased accordingly. But care has to be taken that the additional SIDL deflection is calculated for a composite section and not just the girder section alone.

I have been trying to find a copy of the Bridge Geometry Manual it does not seem to be listed in the PCI book store, I would appreciate if any of you can share a link to this resource online.

Again, Thank you for the answers!

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