Stress analysis on cylinder with slotted OD

[Roylance]

I’m looking at stress distribution in a cylinder which has several significant slots running along part of it’s length. I’d like to perform some illustrative calcs on it to establish some “independent” ratings to compare with those that I’ve obtained from several FEA analyses. One figure in particular that I’d like is the collapse rating through the wall section of the cylinder at a slot. In cross section, the cylinder could be considered as having a splined OD. The slotted sections are obviously supported by the full OD sections with this support diminishing as the distance increases from the slot side. I expect that the support effect of the main OD will be in with radial stress. I see insignificant support from the OD with respect to hoop stress. Stress concentration is obviously also a factor at the abrupt changes in geometry but I’d like to come up with an approximate figure for stress on the slot floor that takes into consideration the support of the full OD.
Any advice/opinions gratefully received.