Box Beam Configuration 3

[JackTrades]

I'm in the initial design stages of a 40-foot span x 18-foot roadway box beam bridge (which will be subject to loads greater than HL-93) and have two questions:

1. Would either of the two (file attached) superstructure configurations have an advantage over the other for design or constructabilty reasons.

2. As the bridge will be constructed on a gravel surfaced roadway and I've got weak clay for about 10 to 15-feet below grade from the top of slope on both sides, would it be reasonable to found it on an integral abutment system and provide approach slabs on both ends?

Thanks in advance for any and all help.

Jack

 

[crossframe]

it appears you are talking about butted box beams. At 18 feet wide, set the box beams level and make up the cross slope in the deck/topping slab. Much easier to get the transverse post-tensioning aligned that way.

 

[BridgeEI]

Agree w/ crossframe on the orientation. If you're using box beams you won't be able to make the abutment integral since the beams are butted together.

 

[bridgebuster]

I would make up the crown in the overlay, too.

The link below will lead you to the NYSDOT standard sheets for IA bridges. You can do it with box beams.

https://www.nysdot.gov/main/busines...e-detail-sheets-usc/ie-integral-abutments-usc

 

[JackTrades]

Thanks to you all for your advice. I end up designing a bridge every couple of years, usually of a configuration that I hadn't previously done before, and this forum and your assistance is greatly appreciated.

-Jack

 

[graybeach]

I am curious as to why integral abutments can't be used with butted box beams. Is it because the stem can't be made intergral with the beams? If so, I think you could still fix the bearings on both ends with dowels, and make the approach slabs jointless over the backwall. NYSDOT has information on this along with some caveats as to positioning the box beams to avoid excessive slab thickness.

 

[BridgeEI]

When I think of an integral bridge, not only do you eliminate the joints but the superstructure should be tied into the substructure (ie the entire bridge should act as a frame). With box beams that are butted togther, I don't see how you get the rigidity to tie the super & substructure together.

From looking at the details that bridgebuster posted, the beams sit on the seat but aren't tied to the abutment other than through the bearing pad. In my mind the only way I could see it being integral was if the extended backwall and beams were post tensioned.

I'm just a young guy so I'd really like to hear from others that are more knowledgeable about the subject. Sorry to hijack the thread JackTrades.

 

[bridgebuster]

BridgeEI - look again. The deck and the approach slab are tied to the backwall.

 

[BridgeEI]

I didn't see that, I just saw the bond breaker on the approach slab. I also didn't see that the strands were extened into the backwall. Thanks for clarification.

 

[bridgebuster]

no problem