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St. Louis, Missouri; the first major bridge over the Mississippi River, the first rail bridge over the Mississippi, and the world's first steel-truss bridge.
In 1867, a group of St. Louis businessmen formed the St. Louis Bridge and Iron Company and hired James Buchanan Eads to design and build a bridge. Buchanan had made his fortune by finding ways to rig barges to salvage sunken steamboats on the Mississippi River and had gained a very favorable reputation during the Civil War by building eight ironclad gun ships in 100 days, but he had never designed nor built a bridge. Despite his lack of bridge-building experience, Eads was convinced he was more than capable of completing the task.
Eads faced a number of challenges, most of which were the result of legislation passed by the U.S. Congress in 1865-66. That legislation specified that any bridge over the Mississippi River at St. Louis must have a central span of at least 500 feet and access roads at least 50 feet above ground level. The restrictions had been included in the enabling legislation because ferry boat operators, steam boat companies, and Chicago businessmen feared the competition that a bridge at St. Louis might create. Eads determined that the best way to span such a huge distance was with a steel arch, and that the foundation of such an arch needed to rest on bedrock. His final design called for three arched spans (two of 502 feet and one of 520 feet) over the river, each supported by a massive limestone pier at each end, with a standard masonry bridge at each end acting as access roads.
Since Eads insisted that the bridge foundations had to rest on bedrock, he designed and built air- and water-tight metal caissons that were sunk to the river bottom to become the bases of each pier. He also invented a sand pump to remove sand, gravel, and silt from the inside of each caisson so that it coult continue to sink toward bedrock as the pier itself was built atop it. This was the first time such a system had ever been used, and the deepest submarine work ever done to that time (each caisson had to go through over 100 feet of sand to get to bedrock). The steel arches Eads used for the bridge were also unique to the day, being the first time cast steel had ever been used in a construction project. The spans were built in cantilever fashion, with construction starting at each end and working toward the middle. To avoid disrupting river traffic, Eads devised a special crane that rested on the completed part of the bridge, eliminating the need for scaffolding or bracing from below. When it came time to close the arches with specially-designed central tubes, workmen discovered that the tubes would end up being 2-1/2 inches too long to go into place but still be the correct length once installed. Eads solved this problem by cutting each tube in half and then joining the two halves with a right-and-left screw, meaning that the length of each central tube could be changed as needed. Eads made sure to patent every one of his innovations as he went along, including the part of his design that allows any one support member to be removed for repair without having to use falsework for support.
The Eads Bridge was dedicated on July 4, 1874. With a total length of 4,025 feet, it was the world's longest bridge for many years. The bridge cost almost $10 million to build, but it has paid for itself many times over. The two-deck bridge originally carried rail traffic on the lower level and pedestrian and buggy traffic on the upper, but the upper deck was later reworked to carry automobiles. Rebuilt in 2003, the bridge still carries light rail traffic on its lower level and automobile and pedestrian traffic on its upper level. It was designated a National Historic Landmark in 1964, and a National Historic Civil Engineering Landmark in 1971.
Eads Bridge today
This page was last updated on January 27, 2017.