164. To find the weight that would break a square or rectangular pillar exceeding 5 diameters, but not exceeding 30 diameters in length.

Rule XVI. - Multiply the area of the cross section of the pillar in square inches by the weight in pounds that would crush a short prism of one inch square (Tables XXI. and XXII.), and divide the product by 11, added to the square of the length in feet, divided by 2.9 times the square of the least thickness in inches.

Example. - What load would break a pillar of Red Pine 10 feet long and 6 inches square, the weight that would crush a short piece 1 inch square being taken at 7518 lbs.?

7518x36 = 270648

100 2.058 = 131510 lbs.,

1.1+ 2.9x36 or 51 3/4tons nearly.

165. For Cylindrical Pillars: By dividing the breaking weight as in the last example by 1.7, the quotient will give the breaking weight of a cylindrical pillar of the same length, but 6 inches diameter instead of 6 inches square.

166. The safe or working load on pillars should not be greater than 1/10 th of the breaking weight, except those used for temporary purposes, in which case it might be increased to 1/5th for pillars under 15 diameters, and to 1/8th for those under 30 diameters.