The Silver Bridge Collapse
The Silver Bridge connected Point Pleasant, West Virginia to Gallipolis, Ohio by spanning the Ohio River and carrying US 35. It was built in 1928, a suspension bridge using eyebar-chain construction, a technology which had been in use for nearly a century. Several other bridges of similar construction spanned the Ohio both upstream and downstream of the Silver Bridge. At the time of its construction the average weight of an automobile was about 1500-2000 pounds, and a truck was limited to about 10 tons. In 1967, when the Silver Bridge tumbled into the Ohio River during rush hour, with bumper to bumper traffic, those loads were much higher.
The bridge failed on December 15, 1967, and the victims who weren’t killed instantly when their vehicles went into the water either drowned or died from hypothermia. Forty-six people were killed. The towers of the suspension bridge were designed to rock slightly with the shifting loads, rather than have the chains pass over rocking saddles at the top. There were three spans of chains on each side of the bridge, anchor to tower, tower to tower, and tower to anchor. A failure of a single component on either side of the bridge had the potential to cause a complete failure of the bridge.
It was the bridge’s design which led to its failure in two ways. With no redundancy which would prevent structural failure in the event of component failure the bridge relied on diligent inspection and maintenance. Years later it was determined that the design of the bridge had contributed to its poor maintenance, as it made critical components nearly inaccessible for inspection. Engineer and historian Henry Petroski said of the bridge in a 2012 book, “If ever a design was to blame for a failure, this was it.” Petroski found that the design made inspection “all but impossible and failure all but inevitable.”
The bridge failed because a single eyebar, the first link of the chain which descended from the bridge’s north tower towards its anchor on the Ohio side, developed a crack. The crack was formed by wear on the link’s bearing, and deepened through internal corrosion. The technology used for bridge inspections at the time was incapable of detecting the crack. Once the eyebar failed the suspension bridge became a victim of a principle of its design, which is that of equilibrium. The complete collapse of the bridge was sudden and catastrophic, with the entire structure destroyed in about one minute.
The bridge was replaced by the Silver Memorial Bridge, about a mile downstream from where the Silver Bridge collapsed. The disaster raised concerns about similarly designed bridges. A bridge upstream at St. Mary’s was immediately closed for full inspection, and was demolished in 1971 without having reopened. Most bridges of similar construction have been replaced and modern inspections using non-destructive testing have identified faulty eyebars on other bridges allowing for them to be repaired (including the San Francisco-Oakland Bay Bridge).