Vibration Response Analysis Of Footbridge Under Dense Crowd Load

With the application of new materials and the development of construction technology,pedestrian bridges are developing toward lower frequencies,low damping,and large spans.However,under the action of crowds,more and more pedestrian bridges appear to have excessive vibration,causing crowds Unrest and even caused panic among the crowd,causing serious loss of life and property.Although scholars at home and abroad have carried out more systematic research on the load of pedestrians,the study of the load caused by the random walking of dense crowds is insufficient,and the load caused by the walking of dense crowds is one of the important causes of excessive vibration of pedestrian bridges It is necessary to further study the load caused by dense crowd walking.In order to accurately simulate the vibration response of the pedestrian bridge under the free walking action of the dense crowd,the field measurement of the pedestrian bridge and the modification of the pedestrian load model are first carried out;secondly,the characteristics of the free walking of the crowd in the dense state are summarized;finally,the vibration of the pedestrian bridge under the action of the crowd To study the mechanism,this article mainly studies the following points:First,the on-site measurement of a single person passing through the pedestrian bridge was conducted,and the vibration response of the pedestrian bridge was compared with the numerical simulation analysis results,and the existing single-person load model was revised.The on-site measurement of the free walking of the crowd through the pedestrian bridge was carried out.The random load model was used to simulate the free walking of the crowd.The test results were compared with the analysis results.The random crowd load model cannot accurately reflect the load generated by the free walking of the crowd.Secondly,aiming at the phenomenon that high-density crowds pass easily on pedestrian bridges,image observation of the walking state of pedestrians on pedestrian bridges,statistical analysis of the walking characteristics of high-density crowds,and the variation law of crowd pace and synchronization rate with crowd density are obtained.A dense crowd load model is established based on the walking characteristic parameters of the high-density crowd,and numerical simulation software is used to simulate the dense crowd to walk freely through the pedestrian bridge.The test results are compared with the analysis results to verify the correctness of the dense crowd load model.Finally,based on the conditions of crowd loading through the footbridge,the parametric numerical analysis of the crowd density,crowd pace,crowd walking route and other related characteristics of the human-induced load model is carried out,and the vibration response results of the crowd load parameters to the pedestrian bridge are compared.The results show that :(1)When the other variables of the ordered crowd are fixed and the crowd density is low,the pedestrian bridge vibration response increases with the crowd density and pace.When the random crowd density is less than 1 person per square meter,the vertical vibration response of the pedestrian bridge increases with the increase of crowd density.When the random crowd density exceeds 1 person per square meter,the vertical vibration response of the pedestrian bridge increases with the crowd density While decreasing.(2)When the crowd frequency does not exceed 2.5 Hz,the vibration response of the pedestrian bridge increases with the increase of the crowd frequency.(3)When the number of ordered people on the bridge is small,pedestrians walking side by side will have a greater impact on the vertical vibration response of the bridge than pedestrians walking in longitudinal queues,but as the number of ordered people on the bridge increases,this effect will gradually decrease When the number of ordered crowds on the bridge reaches a certain number,the effect of longitudinal pedestrian walking on the bridge’s vibration response is greater than when pedestrians walk side by side.