The South Street Bridge was a marvel of Philadelphia’s Iron Age. With it’s giant iron columns, supporting sections spanning the Schuylkill River, the manufacturers had hoped for more excitement for it at the Philadelphia at the Centennial Exhibition in 1876.
However, in a few months, the bridge’s columns began to crack. Engineers diagnosed the cause as moisture in the rubble fill packed inside, expanding as it froze. They strapped on a series of iron belts that kept the cracks from spreading, but there wasn’t anything engineers could do to retrofit a design flaw at the bridge’s western approach. Beneath the roadbed, brick arches resting on granite piers which, in turn, rose from hundreds of wooden piles driven into the muddy riverbed. Problem was, in critical places, the piles had been driven down through only fifteen feet of mud, as far as packed gravel.
When the gravel shifted, piles slipped, piers tipped and arches cracked. Then, on the 10th of February, 1878, “the crippled arches gave way at the haunches and fell,” as assistant project engineer David McNelly Stauffer later put it. Like dominoes, “arch after arch went down, and the bridge was not much more than a wreck.” There had been no casualties, but the two-year-old South Street Bridge was now useless.