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Roebling and Suspension Bridges: A Thread of Steel
Background Information for Teachers

Biographical Information on John A. Roebling

John Augustus Roebling was born in Muehlhausen, Prussia in 1806 and immigrated to the United States in 1831 with the dream to become a farmer and develop a farming community. He settled in Pennsylvania and founded the town of Saxonburg. With poor soil conditions, his plan for establishing a thriving farming community ultimately failed. However, we should be thankful for this "fortunate failure," as it led him into the field of engineering where Roebling made many significant contributions. While Roebling was working near Johnstown, Pennsylvania at the Allegheny Portage Railroad– an engineering feat in its own right–he noticed that the hemp hawsers (thick rope) used for hauling canal boats along the Allegheny Portage Railroad were breaking easily and causing dangerous working conditions. After investigating the problem, he implemented the idea of using wire to make stronger rope. Consequently, he made the portage system safer and cut down on previous expensive maintenance costs.

In 1844 he started designing and building suspension bridges with his wire rope. His first bridge was the Allegheny Aqueduct Bridge across the Allegheny River. He built many more suspension bridges before he died, each succeeding bridge slightly more grand in conception. (For a succinct timeline of key events in John A. Roebling's life, see Student Handout 1: Timeline of John Augustus Roebling.) After a terrible fire in Pittsburgh on April 1845, he worked to rebuild the bridge destroyed by the fire at Smithfield Street. In these first suspension bridges Roebling created a new and improved anchorage system, which he patented in 1846. During the years 1847-1851, Roebling turned his attention to the D and H Canal where he designed four suspension bridge aqueducts including the Delaware Aqueduct, the oldest wire suspension bridge in the United States and a National Historic Landmark. In 1850, Roebling founds his wire rope factory. (This factory had a long and productive history. See Roebling Online History Archive Main Index.)
His most well-known bridges include the Niagara Falls suspension bridge, completed in 1855, and the Brooklyn Bridge, which ultimately became a family project. After designing and starting this famous New York bridge, John Roebling died from tetanus he developed from a foot injury received while working on the perilous project. Roebling's son, Washington, took over his father's work and, with the help of his wife Emily, finished the vast undertaking of bridging the long distance of 1595" in a single span.

Information on Bridges

The website HowStuffWorks-"How Bridges Work" is recommended for basic information on different types of bridges and how they work.

There are many types of bridges. The three basic types are the beam bridge, the arch bridge, and the suspension bridge. Each has its characteristics and each will therefore find its best use in specific situations.

The beam bridge is a basic flat span supported by two piers at each end. Its limitations are that it can only span short distances without the support of a pier. If the area the bridge crosses is wide, then piers must be built to support a succession of beams. If the valley or body of water is deep, this may be impossible to do. Beam bridges are easy to build and are less expensive than other types, but they cannot be used in every situation.

An arch bridge is a bridge using the semi-circular arch and abutments at either end. The arch is one of the strongest building forms known to man and has existed for thousands of years. The shape of the arch forces weight to be pushed out toward the abutments. The arch dissipates much of the tension. The arch is stronger, but again can only be built in special situations. The span is limited, and it is more expensive to build. A deep wide area can usually not be covered with an arch bridge. There are several historic arch bridges in Pennsylvania. The Rockville Stone Arch Railroad Bridge across the Susquehanna river above Harrisburg is the world's longest stone arch bridge. The arch bridge on the old Pennsylvania Railroad at Tunkhannock has long been revered as an engineering wonder of the world. (See markerTunkhannock Viaduct Historical Marker Page.)

Because neither the beam, nor the arch bridges can attain long spans, the suspension bridge is used for these applications. If abutments and piers cannot be easily built, the suspension bridge may be the answer. John Roebling's reputation as an engineer can be based on many of his accomplishments, but the greatest of these is his design and construction techniques of the modern suspension bridge. The invention of wire cable was paramount to the modern day advancement of the suspension bridge. Just as important though was the invention of a machine that spun the cables at the construction site rather than the factory. The diameter of the main cables on many of the bridges was two to three feet. The length and weight would have made it impossible to transport finished cables to the job site. Roeblings answer was "Bring me the wire, I'll spin the cable here".

For additional information on the Allegheny Portage Railroad and The Roeblings, see Historical Marker pages
markerAllegheny Portage Railroad 1
markerThe Roeblings

Web Sites

HowStuffWorks- "How Bridges Work"

This article written by engineer Michael Morrissey very clearly breaks down the basic components to "How Bridges Work." He defines basic types of bridges, forces working on bridges, and gives helpful diagrams to illustrate these concepts.

Roebling Online History Archive Main Index

This website is a project of the Invention Factory and funded by a New Jersey Council for the Humanities Grant. It is an amazing resource for those interested in learning more about Roebling, the wire company he founded, and the projects they were involved in. It includes both primary and secondary resources. Among their primary source collection are interviews from the people who worked in the wire-rope factory in Trenton and documents written by the Roebling family. "The Story of Roebling" contributed helpful background knowledge to this lesson.

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