process can be repeated again, but probably one or two, or at most, three 

 iterations are required to obtain satisfactory convergence. 



One important point to be made is that the collapse criteria reflected 

 by the expressions for P^3, Pc5» Pc6» Pc7» ^^^ Pc8 ^^^ inherently based on 

 a material which exhibits elastic-perfectly plastic characteristics, so that 

 any effects of strain-hardening are neglected. The assumption is made 

 that once the yield strength is reached, at the critically stressed mid- 

 bay locations according to each of the respective criteria, collapse then 

 occurs. 



Another solution for axisymmetric yield collapse of a ring- stiffened 



pressurized cylinder in the presence of the "beam-column" effect was 



19 

 developed by Kempner and Salerno. Their elastic analysis was pre- 



dicated on the Hencky-Huber-Von Mises failure criterion as applied to the 

 critically stressed fiber at the midbay location. For the usual range of 

 geometries the yield strength of the material is first reached at the ring 

 frames due to the high longitudinal stress on the inner fiber. The authors 

 then considered that for loading beyond this initial yielding pressure, a full 

 plastic-hinge exists at the stiffening rings. Thus, the additional pressure 

 which the shell can support is calculated on the assumption that the shell 

 plating is "hinged" to the ring frames. The maximum additional pressure 

 which the shell can support is then based on applying the aforementioned 

 failure criterion to the total stress at the midbay location. 



38 



