Coupling evacuation model of air-supported membrane buildings subjected to air-leakage based on multi-velocity cellular automaton

Highlights

• Incorporating air-leakage process of air-supported membrane buildings in evacuation analysis.

• Experimenting to test individual velocity under different membrane elevations.

• Building a multi-velocity FFCA-based coupling simulation model to analyze evacuation dynamics in deflating membrane buildings.

• Proposing two indices to manage evacuation in deflating air-supported membrane buildings quantitively.

Abstract

Air-supported membrane buildings may suffer from air-leakage caused by the opening of exit, failure of inflation system or environmental force majeure, which is essential for pedestrians' evacuation but receives less attention. The paper proposes a coupling evacuation model based on multi-velocity cellular automaton by incorporating dynamic air-leakage process in evacuation analysis to quantitatively assess the impact of air-leakage on evacuation. Two factors are considered to determine evacuation process in deflating building— herding behavior caused by panic among crowd and the variation of moving velocity. An experiment was conducted to obtain individual velocity under different elevations of membrane surface to provide practical velocity for the model. Coupling simulation results show that evacuation efficiency can be raised in the deflating building with small population density, which is reduced as population density grows. The maximum capacity of the double-exit building is improved by 24% of the single-exit building. This work offers a possible method to predict crowd movement process and assess the level of security of air-supported membrane buildings suffered air-leakage under emergency from the aspect of evacuation dynamics.

Introduction

Recently, a growing number of buildings with large span and space are emerging, such as air-supported membrane buildings, which have a wide application in public constructions, like stadiums, due to its characteristics of reusability, lightweight, low cost, and quick construction [1]. Such public places usually serve a great number of people, which poses a threat to safe evacuation management.

Air-supported membrane buildings keep structural integrity and appropriate shapes by a tensioned membrane surface and inner pressurized air [2] (see Fig. 1 (a)). When emergencies, such as fires, and earthquakes occur, crowd needs to escape from the building as quickly as possible. With the opening of emergency exits or failure of inflation system or other environmental force majeure, like blizzard and typhoon, the building will gradually become deformable and flexible due to progressive air-leakage, and the elevation of membrane surface will experience a persistent decline (see Fig. 1 (b)). The descending membrane surface can affect evacuation efficiency by obscuring personal vision, causing a panic, reducing individual travel velocity, or changing evacuation routes, which is significant for safe evacuation but has received little attention in evacuation research field.

Previous literature [2], [3], [4], [5] explored air-leakage behavior through field tests and numerical simulations according to ASCE (American Society of Civil Engineers) standards [6], which qualifies air-supported membrane buildings if a 20-min air-leakage duration can be provided for pedestrians' timely evacuation without considering crowd evacuation dynamics in buildings. The influence of fire on the deflating behavior of membrane buildings were also explored [7,8], they analyzed fire temperature field characteristics and smoke flow, providing the basis for further study on performances of safe evacuation. Despite the contribution of those published articles focusing on structural safety of air-supported membrane buildings, few are related to evaluating the level of security of these buildings from the aspect of evacuation dynamics.

Plenty of representative evacuation models were put forward to simulate crowd dynamics, which was divided into macroscopic and microscopic models. Crowd movements in macroscopic models are regarded as fluid flow and are depicted by a series of differential equations [9,10]. To better describe pedestrians' behaviors and interactions, microscopic models are proposed, including social force model [11], floor field cellular automata (FFCA) model [12,13] et al. FFCA model has been widely used [14], [15], [16] due to its advantages of depicting individual behaviors and high computation efficiency through translating the long-ranged interaction to local interaction [12]. This paper intends to build a coupling evacuation model to simulate crowd dynamics in air-supported membrane buildings by considering air-leakage process based on FFCA model.

An increasing number of CA-based coupling models concerning the impact of hazards on evacuation were proposed. Fire safety engineering group at the University of Greenwich had done lots of work related to coupling evacuation in a fire [17], [18], [19], [20], and Gwynne et al. [17] developed buildingEXODUS model considering the behavior of pedestrians who were engulfed in smoke or faced with a smoke barrier. They constructed the redirection probabilities from real fire incidents. Coupling simulations were also conducted to explore how pedestrians evacuating from flood [21], [22], [23]. For instance, Y. Zheng et al. [22] researched the influence of flood spreading process on evacuation dynamics by proposing a modified FFCA model and used four stages to describe moving behavior in such situation. Earthquake is another kind of disaster that affects crowd dynamics [24], [25], [26], [27]. Evacuation and building collapse simulations were coupled based on CA model [24], and casualty estimation became analytical rather than experiential or statistical. Investigating evacuation dynamics in disaster and risk becomes a popular and necessary trend, however, there is a lack of understanding of how coupling simulations between air-leakage process and evacuation analysis can be systematically conducted, as well as its challenges and practical values.

This paper proposes a method to build a coupling evacuation model based on FFCA by incorporating the dynamic air-leakage process in evacuation analysis and assess its safety level in terms of evacuation quantitatively. An experiment was conducted to collect individual velocity under different elevations of membrane surface as input parameters to the model. The study compares evacuation dynamics in two evacuation scenarios and explores the impact of the air-leakage process on evacuation efficiency by calculating the total evacuation time and the number of trapped pedestrians.

The rest of this paper is organized as follows: Section 2 presents the coupling evacuation model of air-supported membrane buildings. Section 3 introduces the experiment conducted to test individual velocity under different elevations of membrane surface. The simulation scenario, results, further comparisons and discussions are presented in Section 4. Section 5 discusses the safe assessment rules in ASCE. Conclusions are summarized in Section 6.