the cylindrical form, the hull structure is far from the ideal case assumed 

 in the theory. 



The problem of the additional elastic stresses due to imperfect circu- 

 larity of the shell alone and their influence on collapse strength has 



44 

 already been considered in the discussion of the Galletly-Bart and 



45 

 Bodner-Berks formulations. These analyses were based on the 



assumption that the ring frames were initially perfectly circular and 



remained so during the buckling and collapse stages of the shell structure. 



For the buckling strength of the overall cylinder structure, the circularity 



and the state-of- stress in the ring frames is of paramount importance 



because local failure of the ring frames could precipitate a premature 



overall collapse just as if no stiffening existed. The ring frames are also 



intended to provide adequate circularity to the shell portion. Pulos and 



59 

 Hom working at the Model Basin have discussed the basic mechanism 



by which the local circumferential bending stresses induced in the ring 

 frames by out-of- roundness when superposed on the axisymmetric 

 compressive stress due to the pressure loading can cause premature 

 yielding thus leading to failure; see Reference 60 for the results of some 

 model t«sts using deliberately out-of- round stiffened cylindrical hulls. 

 Kendrick working at the Naval Construction Research Establish- 

 ment developed an analysis for determining the maximum stresses in the 

 transverse stiffeners of imperfectly circular cylindrical shells. This 

 frame out-of- roundness theory followed closely his earlier work for 



108 



