80 HANDBOOK OF MECHANICAL DESIGN 



Stiffener load P' is therefore 



10,000 X 5 



P' = 



20 



Stiffener area = 0.173 sq. in. 

 P ^ -2,500 

 A ~ 



d 



h 



0.173 

 = 0.25 



■2,5001b. 



= — 14,450 lb. per sq. in. 



From the curve for equivalent column length (Fig. 7) for d/h = 0.25, equivalent 

 length will be 0.39 X 20 = 7.8 in. 



Radius of gyration of stiffener = 0.443 



L 



7.8 



= 17.6 



p 0.443 



(7 = 45,000 



K = 10 (assumed) 



t = 0.051 in. 

 p 



-T = (T tanh Kt 

 A 



= 45,000 tanh (10 X 0.051) 

 = 45,000 X 0.45 

 = 21,200 (approx.) 



DESIGN OF HOLLOW GIRDERS 

 Symmetrical Pure Monocoque Sections 



The derivations of the equations for unsymmetrical sections for semimonocoque structures were developed by 

 Guy L. Bryan, Jr., of The Glenn L. Martin Company. 



In a monocoque structure, such as shown in Fig. 10, consisting of corrugated sheet 



sections for upper and lower chord sections and thin 

 sheets for the web side skin, the maximum bending 

 moment stresses can be approximated closely by the 

 formula 



Neutral 



Transverse 

 frame 



_My 



Jb — —f— 

 -* X 



(7) 



tnrizontal 

 ^ reference 



Fig. 10. — Symmetrical semi- 

 monocoque structure consisting of 

 corrugated-sheet chord sections, thin 

 web side skin, and transverse 

 frames. 



where M = applied bending moment 



y = distance from neutral axis to fibers in question 

 7x = moment of inertia of the cross section about the 

 neutral axis. 



In calculations for this type of section, the thin side 

 skin is neglected in all computations because it is 

 incapable of resisting much compression. The sheet simply dimples. Also, the error 

 resulting from ignoring the strength contributed by the portion of the side sheet in 

 tension is negligible. 



