Study On Contact Force And Evacuation Characteristics Of High Density Crowd

With the growth of global population and the rapid development of economy and society,mass gatherings become more and more frequent.In these mass gatherings,it is easy to cause crowd disasters,resulting in fatalities and injuries.The causes of fatalities and injuries triggered by high density crowd are mainly divided into two categories,one is crushing and the other is trampling.The contact force is the essential cause of the complex flow field,special movement phenomenon and casualties.Therefore,the causes of casualties of high density crowd are set as the main line,and different types of contact forces are studied in this paper.Firstly,according to the instantaneous contact force of individuals before trampling,the controlled experiments were designed and carried out to study the movement characteristics of single and double individuals under the action of different forces respectively.The real contact force is correlated with the pedestrian movement behavior and the quantitative transfer laws of impulse between two pedestrians are studied.In the single pedestrian experiment,the polynomial relation is adopted to correlate the real contact force with the movement behavior and the empirical relations among speed,move distance and exerted impulse are established.In the double pedestrians experiment,when the crowd density exceed 2 m-1 and the exerted impulse does not exceed the individual tolerance,the transmitted impulse increases as the exerted impulse increases and the quantitative relation between the exerted impulse and transmitted impulse can be established by the exponential relation.And the average transmission coefficient increases first and then decreases as the crowd density decreases.When the crowd density is less than 2.5 m-1,the transmitted impulse will continue to decrease.The quantitative relation between the average transmission coefficient and distance can be established by the rational relation.Then according to the sustained contact force of crowd during crushing,the controlled experiments were designed and carried out to study the contact forces of individual in stationary and moving high density crowd respectively.The quantitative relation among contact force,space occupancy rate and speed are studied and the fluctuation characteristics of the time series of the contact force are revealed.In this chapter,the density ranges from 8 to 12 pedestrian/m2,and the corresponding space occupancy rate ranges from 0.57 to 0.87.In the stationary crowd,the contact force increases as the space occupancy rate increases and the quantitative relation between the contact force and space occupancy rate can be established by linear relation.In the moving crowd,the contact force increases as the speed increases under different space occupancy rates and the polynomial relation is adopted to establish the quantitative relations among contact force,speed and space occupancy rate.Based on the autocorrelation coefficient,the Fisher-Shannon analysis and the correlogram-based periodogram,the time series of contact force in high densiy crowd show strong fluctuation,high uncertainty and low order degree.And the contact forces show similar periodic fluctuation characteristics and the average period of contact forces in higher density is larger than that in lower density.A clear discrimination in the Fisher-Shannon information plane is found between contact forces measured in the two conditions of lower and higher pedestrian density.Finally,in view of the high density crowd interacting with the bottleneck easily,the controlled experiments were designed and carried out to study the force on the bottleneck and the relation between the force and evacuation characteristics in emergency situations were established.In this chapter,the width of the exit ranges from 0.5m to 1.2m and it is found that as the width of the exit increases,the force of the crowd on the walls can be reduced to a certain extent,and the force of the male is larger than the female.The quantitative fundamental diagram is obtained and the physically inaccessible region in fundamental diagram of emergency situation is expanded.Combining the force with the classical fundamental diagrams,a three-dimensional fundamental diagram including speed,density and force is proposed.The instantaneous flow decreases with the increase of the force,and the mean value of force when the instantaneous flow is not zero can be used as the critical value to guide the crowd evacuation in emergency situations.This study reveals the laws of contact force and the characteristics of evacuation movement in high density crowd.A lot of experiment data and more detailed quantitative description are obtained.The results not only provide theoretical support for direct real force in crowd as an index of high density crowd risk assessment and also provide theoretical support for building design guide and emergency evacuation.