Eh 



cr R 



A , , 2 , , e 



(.3.,4P^XT 



+ (n -1) (136) 



ttR 

 where X = — . It has become common practice at the Model Basin to com- 



Lb 

 pute I as the moment of inertia of the combined section of one ring frame 



plus an effective length Lg (see Equation (22)) of shell, instead of a full- 

 frame- spacing Lf as was originally suggested by Bryant. This, in a 

 sense, compensates for neglecting the true load interaction between shell 

 and ring frames, (as was done by Bryant in his analysis.) It should be 

 pointed out that Tokugawa's original equation was somewhat more com- 

 plicated than that given above; however, calculations for a wide range of 

 interest indicate that the additional terms included by Tokugawa were 

 practically insignificant. As a matter of fact, it usually turns out that the 

 second term of Equation (136) is dominant in the case of hull structures 

 designed for shallow depths. It is usual to refer to the first term of 

 Equation (136) as a shell term and to the second as a ring-frame term, in 

 accordance with the "split- rigidities" concept. 



Equation (136) as it stands does not permit discrimination between 

 external and internal ring frames; the second term in Equation (136) is 

 based on the assumption that the entire cross section of the ring frame is 

 concentrated at the median surface of the shell plating. If one goes back 

 to the basic formulation of the ring-buckling problem, it is rather easy to 

 ascertain that a more correct ring-frame term for use in Equation (136) 

 can be arrived at from 



