The Brooklyn Bridge main cables
The suspension bridge over the East River in New York City, known everywhere as the Brooklyn Bridge, is often cited as an architectural icon of America's landscape, much like the Statue of Liberty nearby. Few people are aware it could also be described as a large-scale metallurgical experiment. The four main cables of the Brooklyn Bridge have been in service since May 1883. They provide primary support for the suspended structure which weighs more than 6000 tons. Although the burden they bear has been reconfigured several times, the cables themselves remain essentially as they were when the bridge opened for business. This bridge was the world's first major civil engineering structure designed and built with steel wire.
Brooklyn Bridge was created during a period in Western culture known as the Victorian Era, named for the queen of the UK who reigned 1837-1901. It was a time of rapid technological changes in ferrous metallurgy. During that era, female clothing fashions in Europe and America were dominated by crinolines, better known as "hoop skirts". Steel wire was being used in short lengths for things like hoop skirts, but there wasn't any commercial demand for long lengths of steel wire until the bridge project. The definition of metal fatigue provided by on-line Britannica states it is "…a weakened condition induced in metal parts of structures by repeated stresses or loadings, ultimately resulting in fracture under a stress much weaker than that necessary to cause fracture in a single application..." Although engineers and scientists do not fully understand how this happens, many studies are underway. As a simple solution to avert disasters it is normal to design metal structures five or six times stronger than needed. This approach works well with the exception of certain applications such as aircraft where additional weight cannot be tolerated. The study presented here explains how and why the main cables of the bridge are unique. The issue of metal fatigue is introduced for review.
.Author(s): Donald Sayenga