Zhijian Fu

Investigation of combined stairs elevators evacuation strategies for high rise buildings based on simulation

Abstract Based on computer modeling and simulation, the problem of evacuation strategies that utilize a combination of stairs and elevators for high rise buildings is investigated in this paper. First, by using the Pathfinder software, a 28-storey building model with stairs and elevators is established. Then, based on the obtained model, several evacuation scenarios are designed for researching this issue. The simulation results show that the optimal percentages of the occupants evacuated by the elevators, when achieving the shortest evacuation time, is almost not related to the number of evacuated persons and floors. Furthermore, the evacuation time decrease achieved by increasing the elevator maximum speed is not as much as that obtained by increasing the number of elevators. Moreover, when evacuating different age groups, it is found that selecting the aged (slow-moving) people, who may create congestion in the stairs, to be evacuated by elevators can speed up the evacuation efficiently, and selecting the children to be evacuated by elevators can improve the utilization rate of the elevators. Finally, the evacuation with a priority order from lower floors to upper floors is considered. Results show that the evacuation with a priority order from lower floors to upper floors can effectively decrease the congestion on the stairs caused by the aged people, and achieve a faster evacuation rate during most of the evacuation process, although the total evacuation time increases a little.

INTERACTIONS OF PEDESTRIANS INTERLACED IN T-SHAPED STRUCTURE USING A MODIFIED MULTI-FIELD CELLULAR AUTOMATON

Little work has been done before in the study of separating pedestrian flow interlaced. Under open boundaries, the interaction of separating pedestrian flow interlaced in a T-shaped structure was simulated, using a modified multi-field cellular automaton updating synchronously. The free-jammed phase transition diagram of pedestrian flow and principles of the pedestrian interference were obtained. The movement of pedestrians is free flow in the low entrance density. While it is a complete jammed flow with the entrance density increasing to a certain level and little difference existing between the left moving probability and the right moving probability. Thus, the dominant factor influencing pedestrian flow is the interference of opposite pedestrian flows due to changing movement directions. And it is changing to an incomplete jammed flow with this difference increasing. Thus, the dominant factor is changing to the interference of the coincident pedestrian flow and the limitation of the bottleneck.

Numerical analysis of combined buoyancy-induced and pressure-driven smoke flow in complex vertical shafts during building fires

Purpose – The purpose of this paper is to study the behavior of smoke flow in building fires and optimize the design of smoke control systems. Design/methodology/approach – A total of 435 3-D fire simulations were conducted through NIST fire dynamics simulator to analyze thermal behavior of combined buoyancy-induced and pressure-driven smoke flow in complex vertical shafts, under consideration of influence of heat release rate (HRR) and locations of heat sources. This influence was evaluated through neutral pressure plane (NPP), which is a critical plane depicting the flow velocity distributions. Hot smoke flows out of shafts beyond the NPP and cold air flows into shafts below the NPP. Findings – Numerical simulation results show that HRR of heat source has little influence on NPP, while location of heat source can make a significant difference to NPP, particularly in cases of multi-heat source. Identifying the location of NPP helps to develop a more effective way to control the smoke with less energy con...

Modeling pedestrian flow on multi-storey stairs considering turning behavior

Pedestrian flow both in normal and emergency situations (i.e. evacuation) has been widely studied by means of experiments as well as modeling methods. In this paper, an extended lattice-gas model is proposed to reproduce the pedestrian flow on multi-storey stairs during evacuations. Two-stage turning strategy is incorporated into the proposed model to simulate the 180∘ turning behaviors of pedestrians on staircase mid-landings, and some movement characteristics such as walking preference and the probabilistic feature of turning are also considered in the extended model. The effectiveness of the model is demonstrated on different evacuation scenarios with different basic parameters. The results show that turning behavior indeed influences the pedestrian flow under the emergency situation (i.e. the drift force in the lattice-gas model is large) while walking preference has a clear negative effect on the pedestrian flow at the normal situations (i.e. the drift force in the lattice-gas model is small). In addition, the results indicate that the entrance period has more effect on the flow performance when compared with the entrance rate. The study may be useful for understanding the flow phase of pedestrians on stairs and developing efficient strategy for crowd management during evacuations.

Gas characteristics and effectiveness of smoke control systems in elevator lobbies during elevator evacuation in a high-rise building fire

ABSTRACT Elevator evacuation has attracted increasing attention as an efficient transport method in high-rise buildings, which is one of the most complex and interesting areas of modern fire research. Through a 3D numerical model built from ANSYS Fluent, this paper studied the influence of elevator motion on the gas characteristics as well as the effectiveness of the smoke control system in the lobby during elevator evacuation in a high-rise building fire. Pressure distribution, temperature distribution and CO concentration distribution in the elevator lobby were analyzed. It was found that the elevator motion decreased the pressure in the elevator lobby while increased the temperature and CO concentration, which indicated that more fire smoke had spread into the lobby when the elevators moved and the effectiveness of the smoke control systems had been weaken. When the elevator velocity was increased from 0 m/s to 2 m/s, the lowest pressure in the lobby was decreased by 566.7%; the temperature line was mostly above the line representing the still elevator; the CO concentration experienced the most change at the height of 2 m: the highest CO concentration was, respectively, increased by 30.4% and 26.7% when the air supply volume (qs) was 0 m3/h and 20000 m3/h. As the air supply volume in the lobby increased, the pressure was increased while the temperature and the CO concentration was decreased. Changes of temperature lines and CO concentration lines under various air supply volumes were very similar. When qs was increased from 0 m3/h to 20000 m3/h, the pressure in the lobby was increased from 0 Pa to around 8 Pa, the highest temperature and CO concentration were decreased by 23.8% and 87.5%, respectively.

Simulation study of overtaking in pedestrian flow using floor field cellular automaton model

Properties of pedestrian may change along the moving path, for example, as a result of fatigue or injury, which has never been properly investigated in the past research. The paper attempts to study tactical overtaking in pedestrian flow. That is difficult to be modeled using a microscopic discrete model because of the complexity of the detailed overtaking behavior, and crossing/overlaps of pedestrian routes. Thus, a multi-velocity floor field cellular automaton model explaining the detailed psychical process of overtaking decision was proposed. Pedestrian can be either in normal state or in tactical overtaking state. Without tactical decision, pedestrians in normal state are driven by the floor field. Pedestrians make their tactical overtaking decisions by evaluating the walking environment around the overtaking route (the average velocity and density around the route, visual field of pedestrian) and obstructing conditions (the distance and velocity difference between the overtaking pedestrian and the obstructing pedestrian). The effects of tactical overtaking ratio, free velocity dispersion, and visual range on fundamental diagram, conflict density, and successful overtaking ratio were explored. Besides, the sensitivity analysis of the route factor relative intensity was performed.