Stair landing concrete-filled pan design

[cliff234]

I am designing a stair for a fabricator. The intermediate landings are constructed of a 3" slab poured into 12 gage metal pans. The pans span 54" and are "U" shaped sections 18" wide with 1.5" upturned legs. I was assuming that the upturned legs would be fully braced by the slab and that I'd compute the flexural capacity of the pan alone (ignoring the strength of the concrete since there is no flexural reinforcing in the slab). The gage metal pans are not close to working. I am not sure what I am doing wrong. This may be one of those things where a miscellaneous metals fabricator "has been doing it this way for years", and now here I am telling him that it doesn't work. Can someone enlighten me on how concrete-filled pan landings are designed? Thanks.

 

[cliff234]

Just found the answer to my question. There is a publication called the NAAMM AMP510-92 Metal Stairs Manual that is available for free download. In that manual are load tables for various types of pans. My calculations were correct. The pan construction that the fabricator wants to use does not work.

 

[racookpe1978]

Good checking.

 

[Ron]

cliff234...exactly!
You can take the opposite approach and consider the pan to be only a form and reinforce the concrete.
If exposed to weathering, warn the end user that lack of drainage will cause the pan to corrode. If you reinforce the slab, you won't have to worry about that as long as you have adequate edge support for the slab.

 

[XR250]

These systems inevitably rust out when exposed to weather - especially if de-icing slats are used.
I would add re-bar as well as a back up when portions of the pan dissolve.

 

[a2mfk]

Ron- you mean something like this could happen?

We usually use standard floor deck for our landings which makes things simple.

 

[XR250]

I agree with a2mfk - floor deck it the way to go