Study on Movement Dynamics of Crowd Evacuation With Spatial Constraints

Abstract

Modern facilities such as high-rise buildings, metro stations and transportation vehicles are becoming increasingly inseparable part of our daily lives because of the conveniences they offer. However, when facing a disaster such as a fire event or a terrorist attack, large numbers of occupants of these complex facilities have to travel several floors downstairs or upstairs before getting to a safety zone. During the evacuation process, the spatial configuration of a built facility plays a critical role in movement of people during emergencies situations, especially when the ground is unstable. It is noticed that the influence of spatial constraints on pedestrian movement has been examined rather sparsely in extant research. As a result, crowd evacuation performance is investigated in this thesis, taking into account spatial constraints.
Considering that pedestrian movement when descending or ascending stairs may have features different from level movement, we first designed and performed well-controlled single-file pedestrian movement experiments to explore the constraints of stairways. Pedestrian movement characteristics including speed, density and inter-person headway were investigated. The trends of fundamental diagrams covering a large range of pedestrian densities for staircase movement were captured. It was found that with the increase of pedestrian density, the speed decrease rate varies; with the decrease of headway, the speed presents two regimes, i.e., free movement and linear constrained movement. Besides, pedestrian speed has a direct relationship with the number of steps separating pedestrians in longitudinal direction.
Based on the experimental findings and filed observations, a new computer simulation model named Pedestrian Footstep model was proposed. In this model, pedestrian movement is described by Newton equations. The stair dimension features, i.e., the tread depth and riser height are constraints that affect the next-step choice. As a result of this constraint, the equivalent footstep length lines present discontinuity and heterogeneous features for descending and ascending movement. To further reflect the feature that in densely packed situations each stair step can hold one pedestrian, the pedestrian agent in the model occupies a space of varying area. The area size changes with the pedestrian speed. In this way, the model bridges the stair dimension features and pedestrian movement features. Dynamics of pedestrian crowd movement has been analyzed considering different stair dimension features and pedestrian flow situations.
To further explore pedestrian movement dynamics on unstable ground, e.g., ground moving or tilting aboard ships, the proposed Pedestrian Footstep model was further extended to take into account motion induced pedestrian gait adaptions. When compared with general buildings, ship evacuation is unique because ships display a six-degree-of-freedom motion feature due to the periodic water movement and wind influence. As a result, constrained by the kinetic motion of the ground, pedestrian agents in the model can adapt gait according to the motion-induced stability conditions. Simulation results indicate the model can capture the well-known empirical features of pedestrian movement. Then, detailed influence of ship motion on pedestrian walking features was investigated. From the simulation results we can see the effect of ship motion on pedestrian movement features is very complex and nonnegligible. The proposed model can thus serve as a useful tool for evaluating passenger ship evacuation performance.
Although kinetic motions can significantly lower evacuation efficiency, sometimes, the motion of the ground can even benefit the evacuation process, for example, using elevators to evacuate occupants. The efficiency of mechanically assisted evacuation in ultra high-rise buildings was thus investigated. To quantitatively evaluate elevator assisted evacuation process, an event-driven agent-based modeling approach was proposed. This modeling approach can capture not only the movement characteristics of stair-using occupants but also the detailed elevator motion features. The combined effects of occupants’ and elevators’ parameters on the evacuation efficiency have been investigated. Results indicate that the model is helpful to reveal the dynamics of elevator assisted evacuation, and sometimes, using elevators to move all occupants to ground safety point may not be an optimal solution.

Date of Award	8 Aug 2017
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Siu Ming LO (Supervisor)