- Waddell (De Pontibus, New York, 1898) proposes to arrange railways in seven classes, according to the live loads which may be expected from the character of their traffic, and to construct bridges in accordance with this classification.
- Waddell (De Pontibus) gives the following convenient empirical relations.
- (See Waddell, De Pontibus, p. 7.) Now in applying Wohler's law, fmax.