Steam Tunnel Design

[eelssm]

I'm doing a steam tunnel (culvert) for a precast company and wanted to see if anyone had a template or sequence that I could use to guide me through the hand calcs. This is for the cover slab, walls, and base slab. The slab is a 2 way slab.

With box culverts, I have a great software tool but wanted something for this effort. I know PCA has a version, but I wanted to stay in excel if possible. Thanks!

 

[bjb]

I'm assuming you have a cross section that is basically a box. You will have negative bending moments at the corners and positive bending moments at the center of the slabs. You will need two layers of reinforcing to resist the negative and positive moments.

To accurately do this by hand you would need to do something like moment distribution. To be down and dirty (and conservative), you could assume that your maximum moment is (WxL^2)/8 and provide that steel top and bottom of each slab, and also make it continuous around the corners.

The best way is to model your tunnel using analysis software. We use RAM Advanse.

Also, make sure you consider the shear strength of the concrete. You want it thick enough so that you don't need and shear reinforcing in your slabs. You also need your slabs thick enough so that 2 layers of rebar are constructable and you meet all of your ACI clear cover requirements.

 

[jike]

If the steam tunnel goes under a road, you will want to meet the design criteria from your friendly DOT. I believe there are a couple of different loadings which must be considered.

You may still want to consider a heavy truck or fire truck driving over it.

 

[civilperson]

AASHTO Bridge Design applies.

 

[eelssm]

Thanks guys!

I went with wl^2/8 for this effort. The precast company was good with it.

Yeah, it's under a parking lot with H-20 loading criteria.

Thanks again!

 

[bjb]

With your steam tunnel being subject to H-20 loads you should also consider the effect of concentrated loads, not just uniform loads. In my first post I didn't realize your steam tunnel would have traffic driving over it. The approach of figuring out the maximumn simple span moment, and then applying that steel top and bottom and continuous around the corners would still be ok. WL^2/8 may not govern with concentrated loads.