Concrete topping reinforcement

[MichSt]

I’m working on the design of a single span adjacent prestressed concrete box beam bridge with a composite concrete topping/deck and I’d like to know if there are any procedures to calculate the amount of transverse and horizontal reinforcement needed in the topping. Or do you just provide temperature and shrinkage reinforcement in each direction?

In the transverse direction the box beams will be post-tensioned together, but I’m still worried about longitudinal cracks developing in the deck. I may just provide heavier reinforcement in the transverse direction, say #5 @ 9” or 6”, if there’s no way to calculate a required reinforcement in that direction. The deck may crack in that direction anyway regardless of the reinforcement provided just because of the joints between the beams. Let me know what you all think.

Thanks.

 

[SlideRuleEra]

This article does not apply directly to your situation, but I have found the insight expressed here useful for assorted problems when no explicit guidelines can be found
ftp://imgs.ebuild.com/woc/C890023.pdf

http://www.SlideRuleEra.net

 

[broekie]

Michigan DOT provides #4 @ 6" in the transverse direction and #3 @ 10" in the longitudinal direction. They use a 6" concrete deck that is composite with the box beams.

I have no idea how those numbers were developed and suspect that no one at MDOT would be able to tell me either. Just the way it has always been done.

 

[MichSt]

Thanks for the responses.

Broekie – I will basically be going with the reinforcement you have mentioned. This bridge project is actually a county job in Michigan so we’re following MDOT standards for the most part. Also, the reinforcement you mention is what we have used on similar past projects. Once the snow clears and I have some free time I plan to visit some of these bridges to see how they are performing.

SlideRuleEra – Interesting article. I noticed at the end it was published in 1989. Is that true? I haven’t heard of this philosophy catching on in the states.

 

[sqrt]

broekie,
that's interesting I don't think I've ever specified a #3 bar. What will the crazy dots think of next?

 

[SlideRuleEra]

MichSt - 1989 was the publication date. I read the article in the magazine back then, saved it - and have had several opportunities to use that approach (successfully), but not for a bridge deck. Have never heard any more on the subject, however.

http://www.SlideRuleEra.net