Elegant Spans: Suspension Bridges

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Elegant Spans: Suspension Bridges

Overview

The suspension bridge using iron and/or steel as its structural material was a new form of spanning space developed in the nineteenth century. Used for pedestrian, vehicular, canal, and railroad traffic, this new bridge form celebrated the versatility and strength of iron and steel as structural elements. The resultant monumental technology created elegant and efficient bridges which captured the imagination of the public as well as the artistic community.

Background

Spanning space by suspending or hanging a bridge surface from towers dates to ancient times when people in Tibet and Peru used the design as foot bridges in the Himalayas and Andes. However, the modern form of the metal suspension bridge is a product of nineteenth-century designers in the United States, France, and Britain as a response to the increased transportation needs of industrialism.

The American James Finley, from Union-town, Pennsylvania, patented his design of the first modern suspension bridge in 1808. Incorporating metal cables or chains into his bridges, Finley used an empirical method of design to construct spans as long as 250 feet (76 m) and influenced other bridge builders in the first few decades of the nineteenth century.

In the early 1800s Finley's design diffused to Europe where Thomas Telford (1757-1834) and Samuel Brown in Britain and Claude-Louis-Marie-Henri Navier in France built on Finley's original work to create longer and stronger suspension bridges. Relying on the superior metallurgical practices of Britain, Brown and Telford used iron bars to produce their suspension chains and were able to improve on the length, design integrity, and elegance of Finley's pioneering work. For example, Telford's 1826 Menai Straits Bridge, appearing structurally substantial and strong, spanned 580 feet (177 m), a major feat for the nineteenth century.

During the 1820s, Louis Navier, a well-known French engineer and theoretician, visited Brown and Telford in Britain and studied their suspension bridges. Navier combined his theoretical approach to engineering problems with his knowledge of these British bridges and the successful French wire cable designs to shape a new era of suspension bridge design and construction in France for almost three decades. Both the Americans and French substituted wire cables for iron bars because they could produce quality iron wire rather inexpensively; iron wire's strength, dependability, and low cost made it a better choice than the iron bars used by the British. French interest in suspension bridges diminished after a bridge failure in the town of Angiers in 1850. This accident allowed Americans to provide the next major achievements in suspension bridge design and construction.

The use of iron cables became a trustworthy practice and a mature style through the developmental efforts of Charles Ellet, Jr. (1810-1862), and John Roebling (1806-1869). Both men were versed in French suspension bridge activities, including knowledge of the analysis, construction, and design of these bridges. Ellet, who built the first significant wire cable bridge in America at Philadelphia in 1842, and Roebling were rival bridge builders in mid-nineteenth-century America; Ellet's early death in 1862 left Roebling as the chief champion of wire suspension bridges in the period following the Civil War in the United States, a time of rapid economic and industrial growth.

Roebling, a German emigré to the United States, translated his extensive knowledge of suspension bridges into a patent (1847) for spinning wire cable. Used first in several canal aqueducts, the technique, along with a special anchorage method for securing the wire cables, became a hallmark of Roebling's bridge work. A major disagreement between Ellet and the directors of the Niagara Gorge Bridge project gave Roebling the opportunity to complete the road and railway bridge in 1855 with a span of 821 feet (250 m); the success of this bridge enhanced Roebling's reputation as a leading suspension bridge builder. His Cincinnati Bridge, completed in 1867 with a span of 1,057 feet (322 m), matched European designs in elegance and sophistication and served as the model for Roebling's most famous design, the Brooklyn Bridge.

With a central span of almost 1,600 feet (488 m) and its massive twin Gothic arch towers, Roebling's Brooklyn Bridge represented the culmination of the nineteenth-century suspension bridge design. In 1869 John Roebling died of complications from a site inspection accident and his son, Washington Roebling, who was well versed in his father's methods and techniques, supervised the remaining work of building the bridge. Completed in 1883, the bridge was the longest suspension bridge in the world, a record it held for many years.

Impact

The Brooklyn Bridge symbolized the impact of the industrial revolution and its attendant age of progress. At a time when the Western world, and the United States in particular, was being transformed by technology, this bridge mirrored the attributes of this new era.

In scale alone, the Brooklyn Bridge was a major achievement. The bridge spanned almost 3,500 feet (1,067 m) with towers reaching 276 feet (84 m) above water level. The New York City area had never seen a structure this high nor long, and it dominated the landscape of lower Manhattan and Brooklyn in the last two decades of the century. Before skyscrapers of the twentieth century dwarfed its size, the bridge symbolized the monumental nature of a new construction technology using iron and steel. The size and scale of bridges and buildings accelerated as rapidly as the technology which produced them.

The growing industrial economy of the Western world increased the development of canals and railroads in the nineteenth century, and the suspension bridge was an efficient and economical means of spanning space in these transportation networks. This bridge design was attractive for those settings requiring an uninterrupted passage, especially for ships, or for locales where an especially deep gorge made it impossible to construct a supporting pier. In addition, the weights of canal aqueducts and railroad lines required stronger bridges so metal became increasingly important as a construction material. By blending strength and economy, the suspension bridge was a natural solution to these transportation needs and contributed to the transportation revolution of the time.

Roebling's techniques for spinning wire cable and erecting towers with the caisson method were innovations in bridge technology. These techniques, which allowed for the widespread use of the suspension bridge, stand as significant American engineering contributions to civil engineering in the nineteenth century—a time when American engineers gained a reputation for blending ingenuity and empiricism into successful and striking projects. Results of this kind reflected the vernacular style in which functionalism, a design based on form following function, determined the aesthetics of a structure. The blending of innovation with functionalism created a unique American motif characteristic of the industrial age.

As a prototype for suspension bridges, the Brooklyn Bridge represents the impact of that bridge style on the social and cultural fabric of America. By providing a regular and dependable connection between Brooklyn and Manhattan, this bridge allowed for a population expansion in the greater New York City area. This growth helped to transform New York City into a thriving, teeming metropolis that became a modern city by the turn of the century. Roebling's design of a pedestrian walkway across the bridge provided a place for walkers and for relaxation on benches, as well as a venue from which to enjoy city views. The multi-purpose function of the bridge, and others like it, has made it attractive to vehicular and pedestrian traffic since its inception. Cities such as New York and San Francisco, surrounded by water, continue to depend on a series of suspension bridges as foundations to their transportation and commercial networks.

Along with the impact on transportation technology and the quality of urban life, the aesthetic qualities of the suspension bridge captured the attention of the artistic community from writers and poets to painters and photographers. Georgia O'Keeffe, John Marin, and Joseph Stella memorialized the bridge on canvas with paintings that celebrate the interplay of forms and shapes typical of suspension bridge geometry with its many cables against a backdrop of towers and urban skylines. The American photographer Walker Evans created a series of dramatic photographs of the bridge from above and below its deck and Hart Crane's poem, "The Bridge," reflects power of the bridge on the creative imagination. This monumental technology became a worthy subject for art as both symbol and artifact of a world which was becoming increasingly a creature of science and technology.

The modern suspension bridge grew out of the newly developed structural technology of iron and steel. As a handmaiden to the growth of railroads, harbors, ports, highways, and urban centers, this elegant style remains closely identified with the power and influence of industrialism in shaping the lives and landscape of the last half of the nineteenth century and beyond. It allowed the spanning of previously unbridgeable space with a physical object whose aesthetic and monumental profile continues to capture the imagination and admiration of both the artistic and technical communities. This bridge design stands as a celebration of the ingenuity of engineers and the elegance and artistry of an efficient and economical means of closing wide and deep spaces in cities, along waterways, and in steep terrain. The pioneering genius of men like John Roebling laid the foundation for a timeless design which reflected a new industrial age of technological progress.

H. J. EISENMAN