L is the effective length of that portion of the cylinder 



which loads the heavy frame. 

 p-Q is the critical pressure of the cylinder with the heavy 



frames replaced with typical light frames (see Figure 



19). 

 n is the critical buckling mode associated with Pg. 



Lr is the spacing between typical light frames. 



Li is the spacing between intermediate heavy frames. 



F 



p is equal to p_, or p , whichever is lower. 



p-p, is the critical pressure of the uniformly stiffened 



cylinder of length Lt^, (see Figure 19). 



p is the critical pressure at which the critical mode 



n 



changes from n to (n+1) as the length of the uniformly 

 stiffened cylinder is reduced (see Figure 19). 

 Thus, the size of the heavy frame in the pressure range P > P„ ^ Ptd is 

 dependent upon two limiting conditions. For the lower limit p-g, the heavy 

 frame is equal in size to a typical light frame and the load acting on it is 

 the pressure over one typical frame spacing of shell. As the heavy 

 frame is made larger, it assumes increasingly more of the total load. At 

 the upper pressure limit p , the maximum pressure for which there exists 

 an overall symmetrical buckling shape in the longitudinal direction, the 

 heavy frame is loaded by the pressure acting on one heavy-frame spacing 

 of cylinder. 



105 



