DESIGN OF LAMINATES 



6-35 



or F 



and r = 



where P C] 



E 



I 

 A 

 r 



L' 

 F„, 



_ P cr 



A (7) 



n 2 E 

 L\2 



I 



A 



= critical load - lbs. 



= modulus of elasticity below the proportional 

 limit - psi 



= moment of inertia - in.'- 1 



2 

 = area - in. 



= radius of gyration - in. 



= effective length - in. 



= critical stress - psi 



(6. 18) 



(6. 19) 



The effective length, L', will be the length of the specimen for a pin-ended element, one 

 half the length for a fix-ended element and twice the length for a free-ended element as 

 shown in Fig. 6-24. 



Fig. 6-24. Effective Length 

 of Column 



4 



PI N ENDED 



b. FIXED ENDED 



