Broughton Bridge Collapse

Bridge collapses from resonance are a rather uncommon phenomena.  One of the most well-known bridge collapses is the Tacoma Narrows bridge.  This suspension bridge oscillated widely.  These oscillation finally caused the bridge to collapse.  However, this was not the first suspension bridge to collapse from resonance or oscillation.  On April 14, 1831, the Broughton Bridge collapsed after a column of 74 soldiers marched across the bridge.  The bridge was found to have lost a bolt at a key point that anchored the base to the bridge.  Surprisingly, that connection was only made by one bolt.  This lack of stability made the bridge prone to vibration.  When a small detachment of soldiers marched across the bridge, they increased the vibration so much that the bridge broke.  These 74 soldiers headed across the Manchester, England bridge marching in step with each other.  They were surprised to feel the bridge slightly vibrating and decided to match their marching with the bridge’s vibration.  The vibrations increased in intensity as the soldiers’s aided it.  Finally, just as the column reached the other side of the bridge, the bridge collapsed.  Nearly forty soldiers were thrown 15-16 feet into the river below.  Due to the shallowness of the river at that time, none of the soldiers were killed.  Many of those who fell into the river were badly injured, but they seem to have recovered.  Because of this incident, the British army never marches over bridges.  To this day, it is the policy to break rank, or for each person to walk at their own gait, when crossing a bridge.  This decreases the likelihood that many people will be in the same rhythm that could activate the resonance in a bridge.



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