Design timber deck for shear?

[darogers]

I have a small bridge with rolled steel beams and a timber deck. I have the steel beams spaced at 2.5' and an engineer working with me sized the transverse timber deck members for flexure and used a 4x8 member (nominal) set flat-wise. The engineer did not check the timber deck for shear due to AASHTO LRFD 8.7 stating that timber decks don't need to be designed for shear. If shear is checked it doesn't come close to working. Does anyone know the basis for the AASHTO statement? To get it to work we would have to go to a wider and thicker member. I don't do a lot of timber design, but I'm hesitant to blindly follow AASHTO and I'm curious to know the background.

Thanks

 

[graybeach]

Just read 8.7 in the 2010 AASHTO LRFD twice. I can't see where it says decks don't need to be checked.

 

[PEinc]

I also believe that you check the timber deck shear at a distance, d, from the deck beam where d is the depth of the timber decking. This helps reduce the shear a lot because there usually isn't much spacing between deck beams.

http://www.PeirceEngineering.com

 

[darogers]

I should have clarified which AASHTO. I was referencing the third edition, 2004. I checked the fourth edition, 2007, and it is no longer mentioned. I agree PEinc and my check did account for that. I am going to design for it, but it would be nice to know why it used to be in AASHTO.