RANDOM VIBRATION OF FOOTBRIDGE GENERATED BY CROWDS’ TWO-WAY WALKING

This paper investigates the crowd-footbridge random vibration in the consideration of a two-way walking of crowd. For this purpose, a random vibration model is developed. In this model, the gamma distribution, widely used in traffic flow theory to describe the headway distribution, is adopted to generate the crowd flow. FFT technique is employed to obtain load power spectral density (PSD) in the exciting points and then the acceleration PSD of any position is calculated by a pseudo excitation method. The results show that the acceleration PSD predicted by the random vibration model agrees with that evaluated by a time domain method. Also, when the footbridge frequency falls within the frequency bandwidth of a crowd excitation, the excessive vibration caused by crowd-footbridge resonance, has a tendency to exceed the vibration comfort requirement of pedestrians, although the footbridge accords with the current footbridge design code in China. Moreover, the footbridge vibration corresponding to the two-way walking of crowd differentiates from that of a one-way walking. Namely, the two one-way walking effects superpose if the footbridge vibration mode of resonance is symmetrical, or otherwise counteract if it is asymmetrical.