Overhang Deck Design with TL-4 Barrier

[catbar]

I'm currently designing a deck overhang with a TL-4 barrier using AASHTO LRFD. For Design Case 1 (Extreme Event Limit State), the overhang must be designed for the vehicular collision plus dead load moment acting concurrently with the axial tension from verhicular collision force.
Does that mean that I can use the Ft and Fv values shown in Table A13.2-1 or would I have to calculate the collision force and axial tension based on
Article A13.3.1?

 

[bridgebuster]

Use the table. A13.3 is for test specimens.

 

[catbar]

Thanks for replying Bridgebuster.

All examples that I've encountered thus far somehow incorporate the Mw, Mb, Mc and Lt of the barrier that has met the TL-4 standards to calculate the Lc. Then they use Lc to calculate Lb. The Ft is then distributed over the length Lb. Lb is equal to Lc+2H (H = barrier height).


Should I disregard the above method and use the Ft listed in Table A13.2-1 and distribute it over the listed Lt instead?


Thanks.

 

[bridgebuster]

Distribute the force over Lb. Look at AASHTO A13.4. Some states use a factored Ft as the design force; usually 4/3 Ft and others use Rw.

 

[catbar]

Thanks Bridgebuster.

I work in NY and we are using the single slope concrete barrier (shown in the Bridge Detail Drawings on the NYSDOT website). Is it common practice to calculate the Mb, Mc and Mw or are these values already published by NYSDOT somewhere. I looked at an example provided by the Arizona DOT and in there Bridge Manual they include a table that lists Mb, Mc and Mw for the barriers used throughout their state.

 

[bridgebuster]

I also work in NY, unfortunately the Bridge Manual doesn't provide much info on overhang design. Have you looked at the Blue Pages? I've done LRFD design but not in NY. The project I'm on now for NYSDOT is LFD but we still had to do the overhang design.

 

[3Fan]

The Ohio DOT put on some training seminars back with LRFD was introduced to Ohio. They went through several examples. Here is a linky to the reinforced concrete seminar that has a well worked out deck design and overhang design. The Deck Overhang Design begins on page 176 of the PDF. Maybe it will shed some light on your question.

ODOT Concrete Design

 

[rebarstud]

The LRFD bridge design examples published by the FHWA in their steel bridge desigh handbook may help.

http://www.fhwa.dot.gov/bridge/lrfd/fhwanhi04041_steel.pdf

Or some of the design examples from NSBA:

http://www.aisc.org/contentNSBA.aspx?id=20244