io6 



l^OWERS AND TANKS FOR WATER-WORKS. 



In the above formula, the constant, 12, is to reduce the length /, 

 in feet, to inches; r represents the least radius of gyration. From 

 Gordon's formula, the working value of the metal per square 

 inch of section for columns of varying length is found; this, multi- 

 plied by the area of the section, gives the ultimate load. 



To apply the Gordon formula, the length and section of 

 the column must be known or assumed, and from the area of 

 the cross-section the element r can be found bv dividing the 



O 



moment of inertia of the shape by its area, as has been shown; 

 but in general r can be more conveniently found from any of 

 the usual handbooks. In order to further lessen the computa- 

 tions, the following original table is given. 



STRENGTH OF STEEL COLUMNS BASED UPON GORDON'S 



FORMULA. 



Factor of safety of 4 used in table. 20 per cent greater value assumed for steel than for 

 iron columns. 



/ = length of column in feet. 

 r = least radius of gyration. 

 5 = safe value of material per square inch of metal section. 



The table is based upon the Gordon formula for iron columns 

 with a higher value of 20 per cent, which from experiment has 



