|
|
|
| Current Issue |
|
|
| Resources |
|
|
|
Bridging the World
| Article
# : |
13876 |
|
|
Section : |
NATURAL SCIENCE
|
| Issue
Date : |
12 / 1988 |
2,930 Words |
| Author
: |
Emory L. Kemp
Emory L. Kemp is professor of the history of science and
technology and of civil engineering at West Virginia
University. He specializes in the history of bridges and
their preservation. |
In times of rapid technological change, many feel threatened by engineering developments over which the public has seemingly little control. The case for bridges is, however, quite different. The word itself is one of the few technical terms to have a favorable connotation and is frequently used in a very positive sense as a metaphor—such as "building bridges" between different nations, peoples, or outlooks. In addition, the traveling public has extraordinary confidence in the safety of bridges. Despite the public's generally positive attitude—and in certain cases, even affection—toward bridges, little is understood about the impact bridges have had historically on societies or the significant role bridges have played in the advancement of engineering.
Bridges can be considered as a case of pure structure in that their sole raison d'etre is to carry loads, unencumbered by the purposes relating to buildings. Long-span bridges are also a challenge to design and construct because of their size and complexity. Thus, bridges have served as vehicles to advance the art and science of engineering.
It is also important to consider the conditions under which bridge building flourishes. From the technical point of view, the most successful bridges are those in which the properties of the materials used are optimized in the structural form adopted. Although bridge building on a monumental and permanent basis dates, in the West, from the period of the Roman Empire, most of the basic structural forms used for bridges were developed much earlier in widely scattered ancient societies. Like the invention of the wheel, it is impossible to date or locate the first use of a log as beam bridge across a stream. The beam bridge supports itself and any imposed loads by bending, requiring a material that is both strong and flexible. Thus, wood and wrought iron are both ideal materials for bridge members subjected to bending. Modern beam and girder bridges, so prevalent on the American interstate highway system, are descendants of the humble log bridge.
Rope obviously lacks the rigidity of wood, stone, or metal; but it is remarkably strong, nevertheless. Thus, rope composed of vines, hemp, or even leather was used very early on to build suspension bridges, maximizing its tensile properties. By the beginning of the Christian era, the Chinese had employed wrought iron chains in place of rope to build impressive bridges to serve both commercial and military purposes.
As an empire with a well-developed iron industry, and in need of road network, the
...
Read Full Article
Look for this article in Ask.com
|
|
