Wide Concrete Stairs on Grade

[Civ-StructEIT]

Hello Folks,

I have been tasked with designing some exterior concrete stairs. The stairs are pretty limited in length, only 3 risers at 6" each and 3 treads at 1'6" each, but are expected to be 40'-50' wide. They are not attached to any building, just a 4" concrete sidewalk at the top landing. My original thought is that a typical stair design with foundation, waist, etc. would not be necessary, and that the stairs can be poured with a continuous bottom elevation, resulting in the concrete depth at the bottom landing to be ~6 inches, and the concrete depth at the top landing to be ~18". Pretty simple design, but since this is in the Northeast US, my concern is with frost heave. Designing it this way, with 12" of crushed stone for subbase and joints every 10' seems reasonable to me, but would appreciate it if anyone has any additional thoughts or criticisms on this approach before I move forward.

Thanks in advance.

 

[dhengr]

Civ-StructEIT:
Many of these steps are built with stepped foundations at 8, 10, 12' o.c. These foundations are then infilled as a base on which to cast the actual steps which span from found. to found., and it is assumed that the infill will settle and the deeper foundations will protect the steps against frost heaving. But, if it is only four treads and three risers, and you also assume that the sidewalks can tolerate the frost heaving, why not just cast the steps directly on grade? Maybe with a grade beam at the top and bottom which allows support and tie-in btwn. the step and the sidewalk above and below. Put a control joint atop each found. wall.