Stair Pan Analysis

[exchange]

I'm checking the design of a steel pan for a staircase. It consists of an 1/8" steel plate with 3" unreinforced concrete.
The stringers are 4'6" apart, and the length of the landing is 6'-0"
Should I consider this plate supported on 4 sides acting as a 2 way slab, or a one way slab spanning the 4'6"?
And, do I consider the concrete as acting?

 

[Ron]

2 ways to approach....
1) Neglect the concrete, compute the bending as simply supported beam. Check shear on the welds at the stringers. Don't worry about deflection, the concrete will fix that.

2) Analyze as simply supported concrete beam. It is too narrow to act as a slab.

 

[dik]

It might help if the top lip has 1/4" or so bars across or straps to stabilize the bent steel channel toe. 3" deep x1/8" thick may tend to buckle. If salt use is an issue, keep sufficient cover to protect the ties, else the steel expansion caused by corrosion can spall the concrete... have seen this happen (also with old time nosing bars).

 

[exchange]

Thanks,
Am using a thicker steel plate - with underside ribs.
Also found that The AISC Manual Pg. 2-145 is a great help in plate sizing.
It's for simple supported plates. If anyone knows of the moment factors for plates supported on 3 and 4 sides for different length to width rations, it would be appreciated.

Thanks Again!