Introduction - Computational Analysis and Design of Bridge Structures - page 3

Introduction
1.1 HIstory of BrIdges
Throughout the late nineteenth and early twentieth centuries, both
structural analysis and material science have undergone tremendous
progress. Before that time, man-made structures, such as bridges,
were designed essentially by art, rather than by science or engineer-
ing. Theory of structures did not exist, and structural knowledge was
extremely limited. Therefore, bridges designed in that period were based
almost entirely on the empirical evidence of what had worked previ-
ously. As the principles governing the structural behaviors were better
understood, computations of those principles came to serve as a guide
to decision making in structural design. Simultaneously, with the pro-
gression in production of the main bridge material, concrete and steel,
bridge design has become more science than art.
In ancient times, bridges were built from easily accessed natural resources
such as wood, stone, and clay with very limited span lengths, until mortar,
the early form of Portland cement, was invented. With mortar material
and the arch structure shape, Romans were able to build strong and light-
weight bridges and even long viaducts, such as the one shown in Figure 1.1,
which is built in the first century. In the seventh century, China was able
to employ cast iron as dovetails to interlock stone segments during the
construction of the Anji Bridge as shown in Figure 9.1, which is still in use
after surviving numerous wars, flood, and earthquakes. Techniques did
not improve until the eighteenth century when new scientific and engineer-
ing knowledge was more widely known. New construction material, iron,
especially the cast iron in mass production, enabled the creation of new
bridge systems such as trusses. The world's first cast iron truss bridge was
built in Coalbrookdale, Telford, England, in 1779, shown in Figure 1.2.
This bridge is still in use carrying occasional light transport and pedestri-
ans. Modern bridges are the evolution of the early bridges using modern
materials, concrete, and steel. With the aid of modern technology, espe-
cially after the invention of the computer and the associated computational
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