Instructions on Modern American Bridge Building

by G. B. N. Tower

This formula has been derived from experiments made by the most reliable authorities.

The constant, 1250, adopted for wood in the following formula, is an average constant, derived from the table, of those woods more commonly used.

Now to reduce the formula to the most convenient shape for use, we substitute the value of s, and we have

or

But, to reduce the load to the proper working strain, we must divide this equivalent by 4, the factor of safety, and we shall have

.