Gordon's formula

A column formula. Also called Rankine's formula:

P = \frac{s}{1+a\frac{l^2}{r^2}}

where:

P = the allowable unit stress for the column

s = the allowable unit stress for blocks

a = a constant depending on end conditions, etc.

l = the unsupported length of the column

r = the least radius of gyration in reference to an axis normal to the plane in which flexure takes place