Research on the influence of building convex exit on crowd evacuation and its design optimization

Building exit has always been an emphasis of research in the field of evacuation. Existing studies on crowd flow characteristics at building evacuation bottlenecks usually focus on plane exit, but insufficient attention has been paid to the characteristics of crowd flow at the convex exit. Convex exit can be considered as such a structure like a double-bottleneck linked passage. This paper aims to study the influence of geometric structure characteristics of the convex exit on crowd evacuation and put forward the optimal design strategy of this structure, so as to improve the efficiency of evacuation in an emergency. Using social force model-based software, MassMotion, it is found that convex exit is indeed more efficient and safer than common plane exit in terms of evacuation time and pedestrians' congestion, especially when the desired speed is relatively higher, indicating that convex exits are more suitable for crowd evacuation in case of emergency. Four size-related parameters of convex exit are analyzed in detail, namely the width of the bottleneck at passage (W_p), the passage width (W), the passage length (L), and the exit width (W_e), to find out the optimum design of convex exit. The research shows that the optimal size ratio is that W_p: W: L: W_e equals 1.5:1.75:3.5:1, and as the overall magnification of building size and the number of pedestrians increases, the evacuation time gradually tends to a stable value, which indicates that this optimal ratio has good adaptability in size effect. Finally, based on the in-depth mechanism of pedestrian flow at the convex exit, three possible application scenarios are proposed to illustrate the feasible optimum design of the convex exit. The results of this study can provide new ideas for research on the structure of building exits.