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Introduction
When
you make a journey, most of your time, unless you are in very
difficult terrain, will be spent on ordinary roads or railways.
The exceptions occur when the builders meet irritants such as valleys,
rivers and mountains. Then the builders respond with works which
range from simple spans to structures which are world famous, and from
plain to beautiful, as the oyster responds to an irritant by making a
pearl.
Who
can look at a bridge across a deep gorge or a wide river without
thinking –
"How
did they do that?".
More
clearly than some other forms of engineering, bridges can be
relatively easy to understand. Not many bridges, especially the
more recent ones, have pointless decoration. Even
where surface treatment has been intended, it has sometimes been left
out, as in the cases of the Clifton bridge, the mighty George
Washington bridge, and the Bayonne bridge. But although structure
must be governed by function, one function may be to please people, by
finding a good balance between form and function. Better to
be obscure because inoffensive, than notorious because ugly.
Understanding
Bridges
These
pages about bridges try to describe simply the structures of the most
common types of bridge. For the
designers and builders of bridges, the techniques are varied and
complex, even without considering the difficulties of the actual
construction process, but the general principles are often reasonably
simple to understand.
Some
of the most ingenious solutions remain hidden inside the structure,
under the ground, or in algorithms and programs of which only the
results are visible. This is increasingly true of many of the
things with which we are surrounded, such as mobile telephones,
television receivers and computers. In a museum of machinery
dating from before the 19th century, we can usually form some idea of
the way things work, though important subjects like thermodynamics are
not often mentioned, and certainly cannot be understood by looking at
machines. None of the exhibits in a museum of modern electronics
would be comprehensible from their appearance.
Although
some bridges, such as suspension bridges, are easy to understand by
sight, others, such as pre-stressed ones, are not, because parts of
the structure are hidden, and of course foundations are always hidden.
Another
important topic is the appearance of bridges, both in themselves, and
as a part of the town or landscape. Every structure, however
small, contributes to the appearance and feeling of a place.
Each object that is not well proportioned and well suited to the
location represents an opportunity lost. Even small footbridges,
that are not famous, and may not be mentioned in books, can
contribute significantly to the impression of a town or a highway.
Topics
are illustrated wherever possible by diagrams or photographs. A number of programs, some interactive, may be downloaded to provide
further insight.
This
web-site only touches lightly upon all the topics mentioned, so links
are provided to numerous excellent sites that provide expert
knowledge, statistics, and lists of large and important structures.
A short list of good books is provided, which provide far more depth
and detail than this web-site. Some of the linked
sites provide much longer lists of books and links than are given
here. |
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