Interactive Lateral Dynamic Behaviours of Girder and Pedestrians

Field measurements were conducted on three bridges to clarify the lateral vibration caused by pedestrians. On the T-bridge the girder lateral displacement was measured during the congested period. It was a clear sinusoidal wave with an amplitude of 8mm and with a frequency of 0.93 Hz, the first symmetric mode. Two pedestrians moved with exactly the same frequency and phase verifying the synchronization theory. On the M-bridge accelerometers were attached to the girder and the pedestrian. This person walked on the bridge in a natural way among other pedestrians. The lateral displacement was a sinusoidal wave with the maximum amplitude of 45 mm and with a frequency of 0.88 Hz, the third asymmetric mode. The pedestrian walks with the same frequency of the girder, and the pedestrian’s phase is between 120 and 160 degrees ahead of the girder. On the W-bridge a group of about 10 people crossed the bridge in line with the same rhythm of 0.87 Hz and 0.66 Hz, the third asymmetric and the second symmetric lateral mode. The maximum lateral girder response is 55 mm at the span centre at a walking frequency of 0.66 Hz, and the synchronization phenomenon is confirmed. The lateral vibration is associated with the torsional vibration. The amplitude is relatively large with smaller number of pedestrians because this is a forced vibration. The lateral girder response at a walking frequency 0.87 Hz is less than that at 0.66 Hz, indicating that the walking frequency with less than 0.9-1.0 Hz may cause the lateral vibration. Observing the pedestrians’ behaviour on these bridges, the girder amplitude of about 25 mm (equivalent to an acceleration of about 750 mm/s2) would be the serviceability limit for the lateral vibration.