John Speller's Web Pages Eads Bridge

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Eads Bridge over the Mississippi River at St. Louis

The Eads Bridge, named after its designer James Buchanan Eads, is one of the most remarkable engineering feats of the nineteenth century. At the time it was completed in 1874, with a total length of 2,147 yards, it was the longest arched bridge in the world. It was also the first substantial structure to be built out of steel rather than wrought iron or cast iron.

The method of construction was also interesting. Like Brunel's Royal Albert Bridge at Saltash (1859) the piers were built using pneumatic caissons. Giant prefabricated iron tubes were sunk into the river bed, and compressed air supplied by steam-operated pumps was used to force out the water. Construction workers then entered the caissons via an airlock and constructed the stone piers of the bridge in the pressurized air. This was dangerous work, since if the workers decompressed too soon there was danger, like divers, of getting "the bends," which sometimes proved fatal. In those days there were no "decompression chambers."This was a particular problem with the Eads Bridge, where the caissons were sunk deeper, and therefore required a higher pressure, than for any other bridge, before or since. Sadly, fifteen workers died and others were permanently disabled.

Another interesting feature of the construction was that instead of building wooden centerings under the arches and using them to construct the steel arch -- which would have resulted in an unacceptable barrier to navigation on the Mississippi, then as now one of the world's most important waterways -- the arches were cantilevered out from above. After the completion of the arch to the center from both sides, the cantilevered superstructure was removed. The final step, realized in Sir John Fowler's masterpiece, the Forth Railway Bridge in Scotland, completed in 1890, was to eliminate the arch altogether and just have the cantilevers.

The Eads Bridge has two separate decks, carrying road and rail routes across the river. It was built to the 4' 8" gauge, which led to the abandonment of the 5' 6" gauge west of the river on the Missouri Pacific, the St. Louis, Iron Mountain and Southern, and the St. Louis & San Francisco Railroads, and also to the abandonment of the 6' 0" gauge of the Ohio & Mississippi Railroad east of the river. The St. Louis, Iron Mountain & Southern, incidentally, managed to convert their entire system on a single day, 28 June 1879. Henceforth there was through rail connection on the 4' 8" gauge all the way to the east coast.

By the 1990s the Eads Bridge had unhappily fallen in disuetude, but it has fortunately now been repaired and restored to use, carrying both some road traffic and the Metrolink light rail system across the river.
The Eads Bridge, St. Louis, Missouri. To enlarge, right click and select "view image"
Diagram showing the Construction of the Piers using Pneumatic Caissons
James Buchanan Eads (1820-1887)
Method of using Cantilever Construction to Build the Arches of the Bridge
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