John A. Roebling - Career

Career

John Roebling and his brother arrived in the United States at an interesting time. The nation was in the later stages of an economic boom, which ended in the Panic of 1837. Farmers were deeply affected by it. A dominant mode of thought in America would be called manifest destiny by the 1840s. Transportation between eastern industrial hubs and frontier farming markets had become a matter of both national and popular interest. Many transportation projects were underway near the location he chose for his colony, but instead of continuing an engineering profession, he took up farming. After five years he married Johanna Herting, a tailor's daughter.

Agrarian work was unsatisfactory to John Roebling, and the colony attracted very few settlers. In 1837, after the death of his brother and the birth of his first child, he returned to engineering as a vocation.

Roebling's first engineering work in America was devoted to improving river navigation and canal building. He spent three years surveying for railway lines across the Allegheny Mountains, from Harrisburg to Pittsburgh, for the state of Pennsylvania. In 1840 he wrote to suspension bridge designer Charles Ellet, Jr., offering to help with the design of a bridge near Philadelphia:

The study of suspension bridges formed for the last few years of my residence in Europe my favourite occupation ... Let but a single bridge of the kind be put up in Philadelphia, exhibiting all the beautiful forms of the system to full advantage, and it needs no prophecy to foretell the effect which the novel and useful features will produce upon the intelligent minds of the Americans.

Roebling began producing wire rope at Saxonburg in 1841. At that time canal boats from Philadelphia were transported over the Allegheny Mountains on railroad cars to access waterways on the other side of the mountains, so that the boats could continue to Pittsburgh. The system of inclines and levels that moved the boats and conventional railroad cars was a state-owned enterprise, the Allegheny Portage Railroad. The railroad cars were pulled up and down the inclines by a long loop of thick hemp rope, up to 7 cm thick. The hemp ropes were expensive and had to be replaced frequently. Roebling remembered an article he read about wire ropes. Soon after, he started developing a 7-strand wire rope at a ropewalk that he built on his farm.

In 1844 Roebling won a bid to replace the wooden canal aqueduct across the Allegheny River with the Allegheny Aqueduct. His design encompassed seven spans of 163 feet (50m), each consisting of a wooden trunk to hold the water supported by a continuous cable made of many parallel wires, wrapped tightly together, on each side of the trunk. This was followed in 1845 by building a suspension bridge over the Monongahela River at Pittsburgh. In 1848 Roebling undertook the construction of four suspension aqueducts on the Delaware and Hudson Canal. During this period, he moved to Trenton, New Jersey. In Trenton, Roebling built a large industrial complex for wire production. This complex inspired the Trenton, New Jersey motto on Trenton's Lower Trenton Bridge.

Roebling's next project, starting in 1851, was a railroad bridge connecting the New York Central and Great Western Railway of Canada over the Niagara River, which would take four years. The bridge, with a clear span of 825 feet (251m), was supported by four, ten-inch (25 cm) wire cables, and had two levels, one for vehicles and one for rail traffic.

While the Niagara bridge was being built, Roebling undertook another railway suspension bridge, across the Kentucky River which required a clear span of 1,224 feet (373m). The anchorage and stone towers were completed, and the cable wire delivered along with the material for the superstructure, when the railway company became insolvent. The bridge construction was halted, and was later finished as a truss bridge.

In 1859 Roebling completed another suspension bridge at Pittsburgh. Its total length was 1,030 feet (314m), consisting of two main spans of 344 feet (105m) each, and two side spans of 171 feet (52m) each.

The American Civil War brought a temporary halt to Roebling's work. However, in 1863 building resumed on a bridge over the Ohio River at Cincinnati which he had started in 1856 and halted due to financing; the bridge was finished in 1867. The Cincinnati-Covington Bridge, later named the John A. Roebling Suspension Bridge, was the world's longest suspension bridge at the time it was finished.

In 1867 Roebling started design work on what is now called the Brooklyn Bridge, spanning the East River in New York. One day in 1869 he was standing at the edge of a dock, working on fixing the location where the bridge would be built, when his foot was crushed by an arriving ferry. His injured toes were amputated. He refused further medical treatment and wanted to cure his foot by "water therapy" (continuous pouring of water over the wound). His condition deteriorated. He succumbed to tetanus 24 days after the accident.

Roebling devised "an equilibrium strength approach, in which equilibrium is always satisfied but compatibility of deformations is not enforced." This was essentially an approximation method similar to the force method: First, Roebling computed the dead and live loads, then divided the load between the cables and the stays. Roebling added a large safety factor to the divided loads and then solved for the forces. This approach gave a sufficiently accurate analysis of the structure given the assumption that the structure was sufficiently ductile to handle the resulting deformation (Buonopane, 2006).