Now to find the necessary sectional area for resisting any strain, we have the following general formula:
a = T ÷ S
or, by substituting the working strenths for the various materials in the formula, we have for wood,
a = T ÷ 2000
Wrought Iron,
a = T ÷ 1500
Cast Iron,
a = T ÷ 4500
But, in practice, cast iron is seldom used except to resist compression.
Strains of Compression. Allowing the same letters to denote the same things as above, we have for