Angers Bridge

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Angers Bridge was a suspension bridge over the Maine River in Angers, France. The bridge is famous for having collapsed on April 15, 1850, when 478 French soldiers marched across it in lockstep. Since the soldiers were marching together, they caused the bridge to vibrate and twist from side to side, dislodging an anchoring cable from its concrete mooring. Though a thunderstorm occurred during the collapse, engineering experts indicate the collapse was due to the soldiers instead of the storm. 226 soldiers died in the river below the bridge. The failure was attributed to a combination of dynamic load and corrosion of the anchors for the main cables.

1 Dynamic Failure of Bridges
2 Results
3 References
4 External Links

[edit] Dynamic Failure of Bridges

As a result of the bridge's collapse, marchers now break step when crossing bridges. Ironically, crowds of people that don't intend to march often start walking in step to match the swaying of the bridge and maintain their balance. The problem is caused by transfer of momentum from the pedestrians to the bridge structure, causing resonance. The same problem occurred in 2000 at the recently completed Millennium Bridge (London), when over 600 people walked across the bridge, causing lateral vibrations. The problem was corrected by installing large dampers to absorb the vibrations, and change the natural frequency of the structure. Vertical oscillations caused the catastrophic failure of the Tacoma Narrows bridge in 1940, when winds blowing at about 40 mph were enough to induce resonance. The vertical waves induced by aerodynamic flutter of the deck, grew in amplitude until the deck failed, and it fell into the waters below.

[edit] Results

The disaster led France to abandon suspension bridges for many years. There had been many similar failures elsewhere (although none so serious in loss of life), and some engineers (like John A. Roebling used reinforced decks in future bridges such as the Brooklyn bridge.

[edit] References

R.E.D. Bishop, Vibration, Cambridge University Press (1965) for a discussion of the engineering problems of unwanted vibrations.
J.P. Den Hartog, Mechanical Vibrations, Dover Publications (1985)