By Luke Carothers
When writing about the history of bridges in the United States, it is easy to focus on the grandiose and spectacular, and rightfully so. Some of the nation’s most spectacular engineering feats are bridges; stories of these projects–such as the Brooklyn and Golden Gate Bridges –fill the pages of our engineering histories. However, solely focusing on the grandiose undermines the full measure of their impact on American society.
When Europeans first colonized North America, many of their villages and settlements were scattered along the bays and inlets of the East Coast. As a result, these waterways served as early highways for European settlers who later became the first American citizens. When American settlers expanded Westward they relied more and more on newly laid roads as well as natural waterways. These early American roads, linking growing cities and settlements, struggled to navigate the dense wilderness in many places, and, in other places, had to contend with crossing wide, strong rivers. In some places, such as Philadelphia, these early Americans built bridges in stone, although this was not the preferred method. Due to the expense and expertise necessary to construct a stone arch bridge, builders often opted for wooden structures using timber felled at the crossing site. Most of these early American bridges were simple wooden truss structures.
However, because of their importance to the local militias, many of these early wooden truss bridges were destroyed during the Revolutionary War. This sparked an intense period of bridge building in the United States as they began to lay the infrastructure that would support a burgeoning population. From the early to mid 19th century, the covered bridge was one of the most popular designs for rural bridge construction. These early covered bridges were timber truss bridges with a roof, deck, and siding. These simple structures were almost always single-lane.
As the population grew, it soon became clear that these single lane bridges were not capable of supporting a mobile population. Farmers who were using covered bridges to transport their crops to market were frequently frustrated by having to wait their turn to use the bridge, giving rise to the modern headache of traffic jams. This issue, coupled with improvements in bridge design and cheaper wrought and cast iron, led to the covered bridge falling out of favor. Whereas timber bridges, particularly covered bridges, require significant upkeep of exposed materials, cast and wrought iron are better suited to being exposed to elements. In addition, these stronger materials were better able to support two-lane bridges.
In 1839, the first cast iron bridge was constructed in Brownsville, Pennsylvania. Constructed after the original timber bridge was washed away in a flood in 1808, the Dunlap’s Creek Bridge was a vital link along the National Road, which allowed America to continue expanding westward. The Dunlap’s Creek Bridge is still standing today, and continues to carry a heavy vehicle load.
As the United States moved through the 19th century, railroads exploded in popularity, and the need for new bridges again reached a peak. Unlike previous bridges, these new bridges had to be capable of supporting the higher loads associated with trains. In order to compensate for these heavier loads, engineers turned to steel, which was easier to produce as a result of the Industrial Revolution. The addition of steel to design allowed for new innovations in design such as cantilevered arches.
Bridge design was further influenced in the later half of the 19th century with the invention of reinforced concrete, which was originally based on a patent for reinforcing thin clay flowerpots with steel mesh. Concrete, which is significantly cheaper to source and use than stone, could easily be molded and transported. When reinforced with steel, concrete also posed a significant advantage over stone in terms of its load-bearing capacity.
These new developments meant that, by the early 20th century in the United States, bridges were stronger and cheaper than ever before. Coupled with the invention and growing popularity of automobiles, these circumstances led to an explosion of bridge construction projects throughout the United States. Particularly amongst rural farming communities throughout states like Missouri, Kansas, and Ohio these early 20th construction projects were vital to the growing mobility of the population and a reliance on vehicular travel.
From the 1940s to the 1960s, rural American communities experienced their largest period of infrastructure expansion. As the nation experienced significant economic growth following World War II, rural communities benefited. In addition, programs enacted by Franklin D. Roosevelt’s government as a response to the Great Depression also came to fruition through numerous rural construction projects.
In light of the challenges the United States will face in coming years such as climate change, economic uncertainty, and aging infrastructure, the history of rural bridge construction in the United States is given a new context. Following the Revolutionary War, an investment in rural infrastructure laid the groundwork for expansion West. When the world was in the grips of the Great Depression followed closely by World War II, a large part of the American response was investment in rural infrastructure. Now, as we face new challenges and scramble for solutions, there is evidence to suggest that at least some part of the solution can be found in rural infrastructure investment.
Luke Carothers is the Editor for Civil + Structural Engineer Media. If you want us to cover your project or want to feature your own article, he can be reached at firstname.lastname@example.org.