LRFD Slab Overhang Design 1

[bridgebuckeye]

I am currently designing a LRFD slab and I was wondering if anyone has any tips on the overhang design. I have the main slab designed, but running into problems with writing the spreadsheet to handle the overhang design.

 

[jimaitken]

What specific areas are you having trouble with?

 

[bridgebuckeye]

the problem is the moments that are required for the collision case or Case I per section 13.4. I downloaded the FWHA example, but they do not show where the moments come from and the Rw value that them calculated I can not reproduce from there example.

 

[jimaitken]

I am not familiar with the FHWA examlpe.
When I have performed this calculation in the past the controlling moment was the barrier strength.This would be the extreme II limit state. I calculated the moment capacity of the barrier then the resistance based guidence from AASHTO LRFD Chapter 13. It has been a few years since I have used LRFD and I know that there have been revisions to the code, but refer to the barrier design section of the most current code for guidence.

This case is then checked to see if it controls design in comparison to the other limit states.

I hope this is helpful.

Jim

 

[broekie]

I worked through some LRFD slab overhang designs, and I found that the Minnesota DOT had some pretty good examples, at least much better than the FHWA example.

Go here:

http://www.dot.state.mn.us/bridge/Manuals/

and look in Chapters 9 and 13 of their LRFD manual for design examples and see if that gets you on the right track.

The design of the overhang is very much dependent on the strength of the barrier that is attached. The theory is that you want the failure to occur in the barrier and not extend into the deck. Therefore, the moment capacity of the deck must be larger than the moment capacity of the barrier in the out of plane direction to withstand the horizontal impact of a truck.

Hope this helps. If you have any specific questions, I can try to help. I'm just starting to use this manual and still trying to work through everything.

 

[jimaitken]

Good reference broekie.