COLUMNS AND STKUTS 105 



Schwarz' formula, whereas in English and American text-books it is 

 called Rankine's formula. 



For / = 0, P = gF, and since short blocks fail by crushing, g is 

 therefore the ultimate compressive strength of the material. 



different methods of end support Kankine's formula takes 

 the following forms. 



.- 



> = 



^ 



One end flat and the other round, 



P 



1+ 1.7S 



87. Values of the empirical constants in Rankine's formula. 

 The values of the empirical constants, / and g, in Kankine's formula 

 have been experimentally determined by Hodgkinson and Christie 



with th- following results. 



i 

 For hard steel, g = 69,000 lb./in. 2 , / = 



For mild steel, g = 48,000 lb./in. 2 , / = 



For wrought iron, g = 36,000 lb./in. 2 , / = 



For cast iron, g = 80,000 lb./in. 2 , / = 



For timber, g = 7,200 lb./in. 2 , / = 



20,000 



1 

 30,000 



1 

 36,000 



1 

 6,400 ' 



1 

 3,000* 



These constants were determined by experiments upon columns for 

 which 20 < - < 200, and therefore can only be relied upon to 



