Handbook of Railroad Construction; For the use of American engineers. / Containing the necessary rules, tables, and formulæ for the location, construction, equipment, and management of railroads, as built in the United States.

by George L. Vose

169. A post may be very well able to resist the compressive strain thrown upon it by any load, but may bulge, or bend, laterally.

The formula by which beams are dimensioned for this requirement, changes with the material, and with the form of section. For rectangular posts of wood, we have the formula below.

W = 2240bd³
L2,

Where W represents the weight in lbs., which may be safely borne,

b represents the breadth in inches,

d represents the depth in inches,

and L represents the length in feet.

170. The value of the formula for the strength of cast-iron posts, seems to depend more upon the authority consulted than upon the nature of iron. For example, assume the length of a post as twenty feet, and the diameter as ten inches; the load which may be safely borne is, according to six different authorities, as follows:—

A	4,000,000
B	181,100
C	370,000
D	940,000
E	307,242
F	300,000

and assuming the length as ten feet, and diameter as ten inches, we have