Introduction to structural integrity
Introduction to structural integrity

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Introduction to structural integrity

3.2 The disaster

The 39-year-old Silver Bridge collapsed suddenly at about 5 p.m. on 15 December 1967 when the roadway was filled with rush-hour traffic – 37 vehicles were trapped on the roadway.

The first signs of collapse were later recounted by the survivors. Many occupants of the cars on the bridge had felt it ‘quivering’ before it fell. Most witnesses had then heard ‘cracking’ or ‘popping’ noises, some saying that it sounded like a ‘shotgun blast’. After this, the bridge started disintegrating fast; girders and hangers fell, followed by collapse of the roadway itself near the centre of the bridge. The towers then fell, bringing the rest of the chains with them. The entire structure collapsed within about a minute, disgorging 31 of the 37 vehicles into the river below. Witnesses on the banks described the bridge falling like ‘a house of cards’, but many tried to save those who had escaped from their vehicles. Those who were trapped inside their sinking vehicles had little chance of escape, however, given that the river reached a depth of 20 m near the centre. Some broke their vehicle windows and managed to escape their sinking or sunken cars, swimming to the surface. The fall from the road deck and impact with the water rendered many of the victims unconscious and they drowned, trapped in their sunken vehicles. The temperature was about −1 °C, and the cold water of the river meant that anyone who survived the fall itself succumbed quickly to hypothermia. Despite heroic rescue attempts from both sides of the river, the disaster claimed 46 victims, although remarkably, three people from the centre section survived.

Recovery of the bodies took some time, and they were the first priority after all the swimming or stranded victims were rescued. However, it was vital to determine the cause of the accident, so the river bed was trawled thoroughly for all the metalwork that had fallen. Since virtually the whole bridge had disappeared (apart from the road deck on the West Virginia bank), this was a big job involving many weeks’ work. It was difficult work as well, because the river was deep and fast-flowing at that point, as well as being very cold.

Although there had been many other bridge collapses in the USA before 1967, only one had been worse: the collapse of a railway truss bridge in 1876 at Ashtabula, in which over 100 died. For such a total collapse to have occurred in 1967 seemed unthinkable, given the progress in analytical design, the greater understanding of loading and the improvement in construction materials that had occurred since the 1920s.

A thorough and intensive investigation was needed to establish just what had happened to cause such a catastrophic failure. Several US government agencies were involved, including the National Transportation Safety Board (NTSB) and the National Standards Bureau (NSB), as well as the Battelle Memorial Institute and several university engineering departments.

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