To find the weight that can be safely sustained by a post, when the height of the post is less than ten times the diameter if round, or ten times the thickness if rectangular, and the direction of the pressure coinciding with the axis, we have -
Rule V. - Multiply the area of the cross-section of the post in inches by the value of C, in Table I.; divide the product by the factor of safety, and the quotient will be the required weight in pounds; or -
W = AC/a (5.)
Example. - A Georgia-pine post is 6 feet high, and in cross-section 8 x 12 inches: what weight will it safely sustain? The height of this post, 12 x 6 - 72 inches, which is less than 10 x 8 (the size of the narrowest side) - 80 inches; it therefore belongs to the class coming under this rule. The area = 8 x 12 = 96 inches; this multiplied by 9500, the value of C, in the table, set opposite Georgia pine, and divided by 6, as a factor of safety, the quotient, 152000, is the weight in pounds required. It will be observed that the weight would be the same for a Georgia-pine post of any height less than
10 times 8 inches = 80 inches = 6 feet 8 inches, provided its breadth and thickness remain the same, 12 and 8 inches.