Abstract: In the dynamic design of pedestrian structures, vibration serviceability assessment is based on the comparison between the predicted human-induced vibrations and the relevant comfort levels. To obtain reliable predictions, walking trajectories and speeds of pedestrians are required to apply the walking loads. Thus, a modified social force model in normal conditions is applied to simulate crowd behaviour on pedestrian structures. This model considers crowds with different densities, geographic areas, travel purposes and directions. Also, different arrival times, initial positions, and initial walking speeds are considered. An illustrative example is presented. Simulation results show that, for pedestrians in the crowd, their walking trajectories are not along straight lines when they are in the state of free walking. Walking speeds show inter- and intra-subject variabilities, and the mean value is lower than that of free walking speed. The global distribution of pedestrians in the crowd varies with time. All these can provide information and reference for getting reliable crowd walking load.