ABSTRACT
Some basic simplifications are justified because of inevitable imprecisions such as deviations of the geometry, non-uniformities of the soil and indeterminable loads. Combined stress analysis is not justified. Therefore, longitudinal analysis, and ring analysis are each considered independently of the other. Concentrated loads are the worst case loads, because loads are, in fact, distributed over a finite area. Ring instability is the worst case of collapse analysis because instability is reduced by the interaction of ring stiffness and longitudinal stiffness.
