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This chapter is essentially a reproduction of a paper delivered by the
author to the Western Society of Engineers at Chicago on September 15th,
1919. It is reproduced here practically in full for two reasons:
First. Outside of the membership of that society, the paper has been
read very little, and it did not, receive any written discussion; consequently,
its contents, as far as this treatise and the engineering profession in general
are concerned, are practically new material.
Second. Unless it be shown herein that most of the information which
had been published about the subject prior to September, 1919, was
wrong, there would not be much use in the author's stating that such is the
fact and claiming correctness for the data thereon which he presents;
because in engineering, as in all other walks of life, any man's word is as
good as another's on a disputed point until one has given absolute proof of
the correctness of his claim. Moreover, from the strictly-professional
point of view, the demonstration of the author's findings and the record of
the various steps which he took in his investigation ought to prove fairly
interesting reading—at least to structural engineers and students of the
specialty of bridge design and construction. But if any reader should feel
averse to wading through this long chapter, he can easily arrive at the
results of the somewhat-elaborate study by skipping to near the end of it,
where he will find a resume of conclusions.
The calculations for the suspension bridges were prepared upon the
basis that the stiffening trusses were free at their ends; but later some more
computations were made in order to determine the effect upon the economic
deductions, under the assumption that the said ends were anchored, but
not fixed, to the masonry. The results showed for both the longer and the
shorter spans a decrease of nearly one hundred feet in the span-length for
equal cost. This is not a serious difference, nevertheless it is well to remember that it exists.
The following is a reproduction of the previously-mentioned paper:
THE COMPARATIVE ECONOMICS OF CANTILEVER AND SUSPENSION BRIDGES
Under the title "Suspension Bridges and Cantilevers—Their Economic
Proportions and Limiting Spans," Dr. D. B. Steinman in 1911 issued a little
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