Excerpt from Specifications for Steel Bridges: Taken From "De Pontibus"

It appears that there is considerable demand by draftsmen and computers for the specifications of "De Pontibus, " but that the book is too expensive to use for specifications only, consequently the author and publishers of that work have concluded to print the said specifications, together with the tables and diagrams, separately from the other chapters - hence this little book, which it is hoped will serve the purpose of the aforesaid gentlemen at one-third of the cost of the original treatise.

A few changes in the specifications have been made in order to bring them up to date, the principal modifications being the following:

1st. The adoption of additional live loads in order to provide diagrams having engines as heavy as any yet built and even a little heavier.

2d. The increase in headroom for railway bridges from 21' 6" to 23' 0" . This is to provide safety for a tall man standing with his hands over his head on a car fifteen feet high. There are such cars in actual use, and several railroad companies are now specifying the greater clearance.

3d. The adoption of rollers surrounded with oil. This is a new detail now used in the author's practice.

4th. A modification of several formulæ for man-power apparatus in rotating draw-spans. The old formulæ required more metal than is really necessary.

5th. - Some slight changes in percentages of elongation on p. 108 (De Pontibus, p. 248).

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