TESTING OF STRUTS. 293 



In the example given the column is of wrought iron, 

 having an I section. The dimensions are : 



Depth of section = Gin. 

 Breadth of flanges = 4in. 

 Mean thickness of metal = in. 

 Length between knife edges = 5-46ft. 



The moment of inertia of the section about an axis 

 through the centre of the web works out to I = 5 '38, and 

 the area of the cross section A = 6'5 square inches. 



The (radius of gyration) 2 



- 5 ' 38 

 6-5 



= 0-829 



On the load being increased, the elastic deflection in- 

 creased until those fibres sustaining the maximum stress 

 were strained beyond their elastic limit, and permanent 

 buckling took place. The maximum load supported by 

 the pillar was 88'7 tons, or 198,0001bs. 



Now, using Kankine's formula, and assuming / to be 

 38,0001bs. per square inch, the values of the other symbols 

 are: 



A 6-5 square inches, 



P = 88-7 tons = 198,0001bs., 



fe 2 = 0-829, 



I = 5-46ft. = 65-52in., 



/ = 38,0001bs. per square inch, 



and, taking 



C rsiutj 

 Eankine's formula says : 



38,000 x 6-5 



4,300 



= 191,5001bs. 

 = 85-7 tons 



Therefore the buckling load as calculated by Kankine's 

 formula is slightly lower than the actual load. 



