Silver Bridge Collapse
On December 15,1967 at approximately 5 p.m., the U.S. Highway 35 bridge connecting Point Pleasant, West Virginia and Kanauga, Ohio suddenly collapsed into the Ohio River.
At the time of failure, thirty- seven vehicles were crossing the bridge span, and thirty-one of those automobiles fell with the bridge. Forty- six individuals perished with the buckling of the bridge and nine were seriously injured. Along with the numerous fatalities and injuries, a major transportation route connecting West Virginia and Ohio was destroyed, disrupting the lives of many and striking fear across the nation.
The General Corporation and the American Bridge Company constructed the Highway Bridge in 1928. It was designed as a two-lane eye-bar suspension type bridge, measuring 2,235 feet in total length, including the approaches. The bridge was designed under the specifications set forth by the American Society of Civil Engineers. The design criteria the society required was an H-15 load demand. The load demand is the weight restrictions and guidelines that the designing engineers must factor into their design considerations.
The bridge was dubbed the 'Silver Bridge' because it was the country's first aluminum painted bridge. It was designed with a twenty-two foot roadway and one five-foot sidewalk. Some unique engineering techniques were featured on the Silver Bridge such as 'High Tension' eye-bar chains, a unique anchorage system, and 'Rocker" towers. The Silver Bridge was the first eye-bar suspension bridge of its type to be constructed in the United States. The bridge's eye-bars were linked together in pairs like a chain. A huge pin passed through the eye and linked each piece to the next. Each chain link consisted of a pair of 2" x 12" bars and was connected by an 11" pin. The length of each chain varied depending upon its location on the bridge.
On December 15, 1967, the Silver Bridge collapsed while it was full of rush-hour traffic, resulting in the deaths of 46 people. Two of the victims were never found. Investigation of the wreckage pointed to the cause of the collapse being the failure of a single eyebar in a suspension chain, due to a small defect 0.1 inch (2.5 mm) deep. Analysis showed that the bridge was carrying much heavier loads than it had originally been designed for and was poorly maintained. The collapse is also linked to several Mothman sightings, leading to the 2002 movie, The Mothman Prophecies.
The bridge failure was due to a defect in a single link, eyebar 330, on the north of the Ohio subsidiary chain, the first link below the top of the Ohio tower. A small crack was formed through fretting wear at the bearing, and grew through internal corrosion, a problem known as stress corrosion cracking. The crack was only about 0.1 inch deep when it went critical, and it broke in a brittle fashion. Growth of the crack was probably exacerbated by residual stress in the eyebar created during manufacture.
When the lower side of the eyebar failed, all the load was transferred to the other side of the eyebar, which then failed by ductile overload. The joint was then held together only by three eyebars, and another slipped off the pin at the center of the bearing, so the chain was completely severed. Collapse of the entire structure was inevitable since all parts of a suspension bridge are in equilibrium with one another. Witnesses afterward estimated that it took only about a minute for the whole bridge to fall.