Research On Evacuation Behavior In Urban Underground Complex

With the continuous development of social economy,limited space on the ground is difficult to meet the demand of high-speed urbanization.Nowadays,many cities in China and other countries have already carried out the planning and construction of their underground complexes integrating commerce,catering and entertainment.Different from traditional high-rise buildings above the ground,urban underground complexes are deeply underground,huge single size and limited in evacuation exit.Consequently,some common problems may occur during the fire emergency evacuation,such as long horizontal evacuation distance,large number of people waiting for evacuation at a same floor,the crowd panic problem,and so on.The most popular evacuation researches nowadays are mainly based on high-rise buildings above the ground,from which the research results cannot be effectively applied to solve the evacuation problems of urban underground complexes.Therefore,it is important to study and solve the existing problems on the evacuation behavior of urban underground complexes at current stage.Research in this paper was conducted in macroscopic,mesoscopic and microscopic dimensions on evacuation behavior in urban underground complexes through model construction,field experiments,software algorithms programming.The main research and results are as follow:In macroscopic dimension,the research on large-scale emergency evacuation behavior in urban underground complexes was conducted with the crowd waiting for evacuation as research object and evacuation model construction as research content.System dynamic model was applied to the construction of evacuation model through interdisciplinary methods.Compared with pretty matured simulation software for evacuation-Pathfinder and FDS+Evac,it was revealed that system dynamic model constructed in this paper was pretty high in accuracy;it integrated the advantages of both successive and discrete models and was free from the restriction of crowd size during the analog calculation;meanwhile,it was able to describe the interaction of individuals within the crowd,reproducing the typical features of group behavior:"faster is slower".In mesoscopic dimension,the panic mood of the crowd trapped in the urban underground complexes was conducted with the crowd waiting for evacuation as research object and the game of individual behavior strategies as main research content.Improved game model for the evolution of group evacuation was constructed on the basis of selfishness coefficient and panic threshold.By simulating the changes of individual behavior strategies,the model reproduced the changes from non-panic to panic mood of the crowd.The research showed that the efficiency of crowd evacuation would decrease with higher selfishness coefficient under non-panic conditions,whereas the evacuation efficiency would be higher with decreasing selfishness coefficient;when overall outcome from the system is stable,the outbreak and large-scale spread of panic was related to the panic threshold of the crowd,and the higher the panic threshold,the more likely they would fall into panic and stampede.Therefore,it was recommended that reasonable measures should be taken to reduce the panic threshold of the system to effectively suppress the occurrence of mass panic and prevent its rapid spread.In microscopic dimension,the research on the influencing factors of the behavior of evacuation route selection was conducted in light of the characteristics of long horizontal distance for large-scale evacuation and complex environment of urban underground complexes.In this research,a part area of an underground complex in city F was selected to conduct field experiments.Five different scenarios were set up to simulate the influence of different factors in the complex environment on the evacuation route selection.In order to make the research results more universal,570 questionnaires were designed and distributed to increase the number of participants.Through the construction of the structural equation model,the questionnaire data was analyzed in depth,and the key influencing factors were finally determined in combination with the results of physical experiments.The research showed that the questionnaires and field experiments had different results due to the different stress environments where the research objects in;illumination conditions,route distance,direction of pedestrian flow and instruction markers had a great influence on the evacuation route selection,and there were certain differences in the effect of various factors in different stress state.In microscopic dimension,with individual evacuees as the research object,considering the complicated evacuation routes in the urban underground complexes,ant colony algorithm was improved on the basis of considering the real-time spread of danger zone of the fire and the model for evacuation route selection of the urban underground complexes was established.The research showed that,compared to the traditional quadrilateral grid map,the hexagonal grid map used in the model would guarantee that the distance of moving in any direction was equal and the moving speed was also equal in unit time;normally,the pace of crowd is vp=1.7m/s;among the four types of products of the fire,CO concentration,O2 concentration,visibility of smoke and dust,temperature,CO concentration is the first one to reach the critical value of safety,so its diffusion velocity was used to determine the spread speed of danger zone of the fire——Vk=0.137m/s;the model could quickly provide a safe and reasonable evacuation route for the trapped people;greatly reduce their stranded time in dangerous areas and avoid straying into dangerous areas or“walk through the wall" during the movement.A software "Intelligent Evacuation Route Search System"(software registration number:2017SR530933)was programmed to try to put the research results into practice.