Art. 71. 



LOCATION OF THE NEUTRAL AXIS. 



101 



one of the parts, when the moment of this part becomes zero. 

 In the above case, with axis Q'Q' 



11 d'= 8X4.25 = 34. 00 and d'= 3. 09 in. 

 This is the sar^c, location as found above for, 

 d == 8.25-d'= 8.25-3.09 = 5.16 in. 



A steel shape, whose properties are given in the handbooks, 

 should riot be divided in the above man- 

 :// ner. Referring to Fig. 73 and "Cam- 

 bria" p, 174, the center of gravity of 

 the angles is 0.75 in. from the back of 

 the longer leg. Taking moments about 

 axis QQ, 



!5 and <i = 2.39 in. 



Fig. 73. 

 13.5 d = 6(6.125 0.75) =6X5.375 = 



For a triangle, Fig. 74, the application ; of equation (14) is 

 as follows. 



Fig. 75. 



Vl = 



This becomes, since x :b ::v' :h and x = 



rh 



2 I 



JO 



72. floments of Inertia. Having located the center of 

 gravity of an area, the moment of inertia about an axis through 

 it (the neutral axis) is found by means of equation (11). /is 

 a quantity of the fourth order the square of a distance times 

 an area. 



For a rectangle, Fig. 70, 

 ' 



/fiA 

 v*bdv = 

 -\h 



This value should be remembered as it is frequently used. 



