Resonance can occur in a variety of systems, including bridges, and it can have both beneficial and detrimental effects. In the case of a bridge's oscillations, resonance can cause the bridge to oscillate at its natural frequency, leading to significant vibrations in the structure.
During the London Millennium Bridge incident, resonance played a critical role in the near-disaster. The bridge was designed to have a low level of damping, making it highly susceptible to resonant vibrations. When the bridge was open to the public, it was subjected to pedestrian-induced forces that caused it to sway back and forth. As the pedestrians walked across the bridge, they caused small lateral oscillations that were amplified by the natural frequency of the bridge. As a result, the bridge began to sway more and more dramatically, leading to a dangerous situation where people could have been injured or even killed.
To address the problem, engineers added a series of dampers to the bridge, which helped to reduce the amplitude of the oscillations and stabilize the structure. The dampers essentially absorbed the energy of the oscillations, preventing them from building up and causing the bridge to oscillate at its natural frequency. Overall, the incident demonstrated the critical importance of understanding resonance in structural design and the potential dangers of failing to account for it.