Encased duct analysis

[Engineermama13]

I need help analyzing the strength of this 26” square encasement(see attachment). I need to know strength of concrete in flexure and shear. 3000 psi concrete and it is going to run horizontally with a max span of 22 ft between piles.

 

[dik]

If you have any soil on top of the duct bank, or traffic over, then the 22' span between piles may be pushing it... I would treat it as 2 - 8" or 10" wide beams with a single leg stirrup for shear reinforcing.

Dik

 

[bridgebuster]

A few thoughts...
[ul]
[li]treat it as a continuous beam, with 22' spans[/li]
[li]analyze like a prestressed box beam, just ignore the prestressed parts of the equations, or[/li]
[li]analyze it like a typical rectangular beam but reduce the effective width by the pipe diameter and assume 2 No. 8 top and bottom, or maybe 2 1/2 #8's.[/li]

#3 ties at 12 seems light. Use 3" cover minimum all around; check the aggregate size of the mix to ensure you leave enough clear distance between the bars and the pipe.