Two Bridges, One Name, The Second

The Washington Crossing Bridge over the Allegheny River has a much shakier claim on the name than yesterday’s bridge. George Washington’s adventures in Western Pennsylvania were limited, as far as I know, to when he was in his early twenties, during the French and Indian War.¹ The French attempted to hold the juncture of the Allegheny and Monongahela River, near the southwest corner of New France, with Fort Duquesne, and much of Washington’s early military career (in the militia of the British colony of Virginia) was spent near that fort. The fort had a multi-army history similar to that of Ticonderoga, and is now the site of Pittsburgh. In any case, on to the engineering…

From the 1880s, when iron- and steel-truss bridges began to really dominate usage in the US, until World War II, long-span arch bridges like this were a small but steady minority, often used specifically for monumental effect. The Washington Crossing Bridge was constructed 1923-24, when there were certainly alternatives to its form and materials, but this is a really nicely detailed set of steel arches and concrete piers. There are three river spans, 353 feet in the center and 323 feet on each side, and multiple land spans over the railroad tracks on each side of the valley. The center is 94 feet above the water.

The most beautiful details from an engineering perspective are those concerning the abutment and center hinges of the three-hinged steel arches. The ribs are riveted built-up members and the hinges are pins, but regardless of the engineering logic this is simply an incredible design:

The small arches between the columns from the deck to the main arches are for show, and only exist at the two outer main arches. The inner main arches are less visible and don’t have that extraneous ornament:

The only thing I’d change if I could would be to get rid of those little arches. They distract.

1. For non-American readers: the French and Indian War is the name that the British colonists in what became the United States gave to the North American portion of the Seven Years War. They named it, as people often do, after their opponents. Regardless of the outcome of the war in Europe, it reshaped North America, with New France being ceded to the British and becoming the basis of modern Ontario, Quebec, New Brunswick, and Newfoundland.