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Synchronous lateral excitation
Pedestrian-induced oscillation phenomenon in footbridges From Wikipedia, the free encyclopedia
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Synchronous lateral excitation is a dynamic phenomenon where pedestrians walking on a footbridge subconsciously synchronize their lateral footsteps with the bridge’s natural swaying motion, amplifying lateral vibrations.[2][3] First widely recognized during the 2000 opening of the London Millennium Bridge, synchronous lateral excitation has since become a critical consideration in the design of lightweight pedestrian structures.[4][5][6]

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Mechanism

Synchronous lateral excitation arises from two interrelated synchronization processes. The first is the pedestrian-structure synchronization, where slight lateral bridge movements (e.g., from wind or random pedestrian steps) prompt walkers to adjust their gait to match the bridge’s oscillation frequency, increasing lateral forces.[7] The second is pedestrian-pedestrian synchronization, where individuals unconsciously align their stepping patterns, further reinforcing the resonant force.[8][9]
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Key cases
- The London Millennium Bridge experienced lateral vibrations up to 70 mm due to synchronous lateral excitation, requiring a £5M retrofit with dampers.[2][4]
- The Auckland Harbour Bridge experienced a lateral frequency of 0.67 Hz during a 1975 demonstration.[10]
- The Birmingham NEC Link bridge experienced a lateral frequency of 0.7 Hz.
- The Toda Park Bridge in Japan is an early documented case (1990s) studied by Fujino et al., informing later synchronous lateral excitation models.[7]
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Mitigation strategies
Some ways to avoid synchronous lateral excitation are the implementation of tuned mass dampers, which were used in the Millennium Bridge to increase damping from 0.5% to 20% critical.[4] Other strategies involve designing bridges with lateral frequencies outside the 0.5–1.1 Hz range as well as managing crows by limiting pedestrian density during events.[5]
References
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