The ordinary concept for beams on elastic foundations whatever the material of the beams is that is supported on soil. Of course one may use such concept to support beams of whatever the kind on something.
If your question pertains to support a beam on a halfspace made of steel you use the formulas for Boussinesq and integrate over the area, if you assume the load is flexible. This study shows how for this case (and for all, something that is not normally enough stated) the modulus of subgrade reaction is a value depending on the area in whic the load is imparted. For example, it takes only about 24600 kgf/cm2 extended on 1 m2 of the steel halfspace to sink it average 1 cm, whereas to sink 1 cm average a 10cmx10cm area you would need to apply ten times more.
