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Differing Degrees of Elegance

That pretty picture is a Detroit Publish Company view of the Upper Steel Arch Bridge over the Niagara River, below the falls. It was built in 1898 and collapsed in 1938, replaced by the current Rainbow Bridge.

The good: It can be difficult to reconcile the geometry of an arch and the supported deck above. In this case, the designers manipulated the pattern of the web members in the arched truss (or is it a trussed arch?) so that half are vertical, and could be extended up to carry the deck girders at a regular spacing. That means the orientation of the web members relative to the arch chords is different at every node because of the curve, but it greatly simplifies the superstructure above the arch.

The bad: the Niagara gets a lot of ice every winter. An ice jam destroyed the bridge by damaging the steel at the abutments. The replacement bridge moved the abutments higher to prevent a repeat of that failure.

The ugly: the problem was foreseeable. It’s not like the ice conditions weren’t well known before construction began in 1897. Shortly after construction, masonry walls had to be built at the river to protect the abutments. Maybe, an arch with a deep rise, graceful though it was, should have been shelved for a solution that moved critical structure farther away from potential damage.