BRIDGESPOTTING

Eads Bridge, constructed in St. Louis in 1874, was not the first bridge to cross the Mississippi, but it is the oldest bridge still standing. The bridge was conceived and constructed by James Buchanan Eads, a prominent military engineer and inventor.

As an early crossing of the largest river in the United States, you can imagine that construction of this bridge set all sorts of records for highest, longest, first use of certain materials and techniques, and other engineering achievements, and it did.

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As part of a common theme among bridges, or anything else new for that matter, Eads’ plan was opposed by steamboat and ferry operators who feared that a bridge would obstruct the river as well as cut into their business. To avoid blocking steamboat traffic on the river during construction, cantilever supports, as opposed to scaffolding, were used for the first time to hold the arches up before they could be completed. Construction of the pneumatic caissons, which needed to be sunk more than 100 feet deep to reach bedrock so that they would not be damaged by scour during floods, resulted in one of the first recognized cases of the bends, killing 15 workers. One of its most important distinctions is that Eads Bridge represented the first use of steel in a major bridge. Much of the complex deck structure was made of wrought-iron, but the important load bearing components of the arches were made of steel. The bridge was, at the time of construction, the longest arch bridge in the world, at more than 6,400 feet long.

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The bridge is actually a complex structure with different construction techniques and materials along its length. On the riverbanks, the bridge is anchored by multi-level stone arch approaches. The lower level consists of five narrow, tall arches. These arches have red granite bases, which are then topped by yellow sandstone. From close up, you can see the cross-bedding in the sandstone, making the arches a geologic field trip all on their own. The lower arches are then topped by another row of yellow sandstone arches, much smaller, that support the upper road deck. Each of these granite and sandstone ends is then flanked by a massive black stone tower, which provides an interesting color contrast with the yellow and red of the arch sections. The black towers are then used as the abutments for the most interesting part of the bridge – the ribbed steel arches. The main part of the bridge consists of three of these arches, each sitting on the two end towers and on two more piers in the middle of the river.

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There is a more detailed description of the bridge, and the surrounding Gateway Arch area, in my book, Bridgespotting Part 2: A Guide to Even More Bridges that Connect People, Places, and Times.