Modeling Ultra-High-Density Exposure and Evacuation Dynamics in a High-Density Urban Plaza: An Agent-Based Simulation Study of Guangzhou Huacheng Plaza

High-density urban plazas hosting multi-session public events often experience pulsed inflows, prolonged crowd retention, and localized bottleneck congestion, creating crowd-safety risks that cannot be fully captured by static capacity or total evacuation time alone. This study develops an agent-based simulation framework to evaluate ultra-high-density exposure and evacuation dynamics in Guangzhou Huacheng Plaza during the International Light Festival. The model was constructed in AnyLogic using site-layout data, event organization records, official attendance information, historical event timelines, and publicly available video observations. Two scenarios were examined: normal dynamic entry–exit operation under different inter-performance intervals, and overload-triggered evacuation under alternative spatial management strategies. Model calibration and event-process validation were conducted by comparing simulated congestion hotspots, key event timing, delayed dispersal patterns, and evacuation-duration ranges with historical observations and documented event records. The results show that extending the inter-performance interval from 90 min to 120 min reduced the overload duration from 75 min to 5 min and decreased cumulative ultra-high-density exposure from 25.62 to 13.93. Under overload evacuation, zonal guidance mainly improved early-stage crowd redistribution, whereas increased exit capacity produced a stronger reduction in total evacuation time and sustained congestion. Total evacuation time decreased from 185 min in the baseline condition to 160 min under the combined strategy, while effective discharge capacity increased from 231.12 to 338.28 pedestrians/min. These findings indicate that crowd safety in open urban plazas depends not only on total attendance, but also on event pacing, bottleneck recovery time, and effective discharge capacity. The proposed exposure-oriented framework provides a quantitative basis for evaluating crowd accumulation and evacuation strategies in high-density open public spaces.