Civil Engineering Reference
In-Depth Information
ELEVEN
A BRIDGE SPANNING A MILLENNIUM
We live in times when children and many adults have learned to think that
the world's fascination resides in shiny screens. Life's excitement, they think,
is in ever newer handheld gadgets or in the newest functions available in
hyperspace. The bridges and other large objects that make up our public
infrastructures reside, however, not in cyberspace but in ordinary space, the
space that human beings have always experienced. To the eye accustomed
to the little screen and uneducated in the meanings and value of the built
environment, these great artifacts seem staid, seem to just sit there.
Yet, as we have learned in this topic, bridges are far from being stag-
nant entities. They span a gap because they are carefully designed to balance
forces of resistance against the dead load constituted by the structure itself,
and against the loads imposed on it by traffic and natural events. The forces
are exerted through basic processes of compression, tension, shear, bending,
and torsion, but in infinite quantitative combinations. Whether a bridge is
supported with girders, trusses, arches, or cable stays, it stands as a carefully
designed structure, dynamically balancing imparted load against structural
resistance, in keeping with constraints of materials and of site. When it is
well enough made, it qualifies as structural art. Well made, the bridge can
serve both as practical asset and as monument.
Good decisions about a bridge are made when more citizens are aware
of the constraints and creativity that go into its making. As we have seen,
some basics of bridge engineering are accessible to those who never would
have considered the study of the subject. In the eyes of those who have
achieved even a basic appreciation, the infrastructure becomes more inter-
esting. For a few, bridge appreciation can even be an avocation, sort of like
bird watching. For some readers of this topic, the planning and engineering
of bridges (and other infrastructures) can even become a fulfilling career. If
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