3.6 Failure sequence
Following the discovery of the broken eye bar near the top of the northern suspension chain on the Ohio side of the bridge (Figure 36), it was possible to reconstruct the sequence of events during the collapse.
When the side chain separated, the entire structure was destabilised, simply because all the loads it supported were immediately transferred to the adjacent parts of the bridge. With its support along the north side of the bridge destroyed, the road deck below the broken chain started tipping over to the north. The hangers holding it up on the south side started breaking, and the deck below the tower broke away. The road deck crashed to the ground on the Ohio bank of the river, taking its vehicles with it as it fell.
The Ohio tower was affected rapidly by the break in eye bar 330, and it leaned over to the north east, with buckling and fractures of its bracing elements below the top. The main road deck in the centre of the bridge was also tipping and dropping as the tower toppled over. As the tower fell, it pulled the south main chain over with it, putting it under enormous lateral load. In the main span, fractures of the hangers occurred on the south side of the deck; as the main chain fell to the north, it impacted the north tower, and eye-bar joints started breaking in the south chain. It was followed by main-chain joint fractures near the West Virginia tower. According to the official account of the disaster, these events occurred up to about 10 seconds after the fracture of eye bar 330. During this phase the road deck broke in the middle, taking its vehicles down into the river. The visual sequence is summarised by one of the eyewitnesses who was about a quarter of a mile away downstream on the West Virginia river bank:
I turned around and looked and saw the Ohio towers (sic) falling. The tower legs seemed to twist counterclockwise (when viewed from the top) and fall upstream and towards the center of the river. The center span of the bridge broke in the middle and fell straight down. It looked as though the cars on the center span all fell with the bridge and looked like they were falling in a funnel – some falling backward, some falling forward. After the center span fell, the West Virginia towers (sic) and span fell … the bridge was all down in a matter of five seconds as I estimate it…
The West Virginia tower was one of the last main parts of the bridge to fall, dropping into the river and facing towards the east. At the end of about a minute the entire superstructure, apart from the stone piers, had disappeared (Figure 35).