Buried concrete box culvert deflection

[TehMightyEngineer]

Quick question as I don't have the PE around to find out what he wants to do until later tomorrow.

Anyone have any thoughts on the total (dead + live) long-term deflection limits for a buried, precast concrete box culvert with 2 feet of soil cover? It's a long span culvert that will be under a highway (non-DOT and there's little to no spec from the EOR) and when I size the structure for strength I'm getting about L/200 (1.3 inches) for total deflection (L/400 live load deflection). AAHSTO only really covers deflection limits for decks directly under vehicle loads. Given the 2 feet of fill the ACI 318 deflection limits don't seem quite applicable.

Thoughts? My guess is that this is an acceptable deflection and will be unnoticeable under the 2 feet of fill and pavement.

Maine EIT, Civil/Structural.

 

[dicksewerrat]

How about 2 12 foot span boxes side by side. Closer to standard sizes. May be easier to set also.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[TehMightyEngineer]

Possibly, but they definitely use more concrete and will require a slightly larger amount of excavation required. I imagine those can both be deal-breakers.

Maine EIT, Civil/Structural.

 

[dicksewerrat]

So this box is 19.5 feet wide and how deep?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[TehMightyEngineer]

19.5 ft span, 10 ft deep (both interior dimensions).

Maine EIT, Civil/Structural.

 

[dicksewerrat]

Then I would use 2 12 ft. wide and 10 ft. deep boxes. you probably have them as a standard item. They will be easier to load/transport and set. The cost will probably be a wash per lineal ft. The 2 12 's will also give them a little safety factor on their flow calc.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[TehMightyEngineer]

I would still think it would cost more for the two culverts rather than the single but you may be right. The single requires less time placing rebar but would obviously require larger rebar. However, you've doubled the interior wall with two culverts so that's going to add some cost for concrete and rebar. They will have to perform the same number of lifts and shipments so that would be a wash.

I suspect the biggest issue is a double culvert would likely require a change order to the EOR. This is likely something the precaster wants to avoid so they probably just prefer to go with what the drawings say. As this project has wrapped up I'll have to inquire on the next one.

Maine EIT, Civil/Structural.