Frequency Dependent Pedestrian Load Model for Lateral Vibration of Footbridges

In an attempt to study the phenomenon of lateral vibration of footbridges thoroughly and propose a solution that captures the essence of the problem, a simplified mathematical model is presented. In this research, a mathematical proof of the linear relationship between the force induced by pedestrians and the bridge local velocity is presented. It is concluded the constant “K” in Dallard’s model is only dependent on damping coefficient of the bridge, not the critical damping ratio. The model emphasizes how the pedestrians will react to the bridge movement as it starts to wobble. A biomechanical model is proposed in this study to model the amplitude of lateral force induced by pedestrians. The model relates this lateral force to the stride (walking) frequency and hence the footbridge acceleration can be determined and compared with comfort level proposed by codes. The proposed model is verified through available full scale testing data and proved to be promising.

In addition, the model emphasizes the importance of the pedestrians’ and bridge masses combined in calculating the bridge natural frequency as they are of relatively comparable weight, especially for long span footbridges.

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