Evacuation time assessment and optimization of high-rise office buildings considering the vertical fatigue of evacuees

Large vertical height of high-rise buildings may induce fatigue among internal evacuees during emergency evacuations, consequently reducing evacuation efficiency and compromising life safety. Therefore, investigating fatigue-influenced evacuation in high-rise buildings holds significant importance. In this paper, a refined evacuation model considering architectural furniture was established by Pathfinder for a real high-rise office building. Based on the evacuation data in the existing literature, the vertical evacuation speed formulas of different age groups considering fatigue were fitted and verified. Subsequently, the effects of fatigue, occupant density, and age on evacuation time were studied, and the engineering evacuation optimization strategies were explored. The study demonstrates that the evacuation time is prolonged by nearly 20 % under the vertical fatigue situation, and this prolongation effect is more obvious after the evacuation starts for 1000s; when the occupant density is 4-6 m²/person, it has a significant impact on the evacuation time. When the occupant density is greater than 6 m²/person, the impact is small. The presence of evacuees aged 61-70 substantially prolongs evacuation time, and the evacuation time will increase significantly when the floor where the evacuees present higher than 6 floors. Based on these results, the formulas for building evacuation time for engineering reference were developed. Simulation results of optimization strategies indicate that the optimization strategy of supplementary outdoor staircases is the most effective when conditions permit. This strategy can effectively alleviate the pressure of the middle stairs and improve the evacuation efficiency. The floor-by-floor phased evacuation is relatively easy to implement in the simulated evacuation strategy. The optimization strategy can reduce the adverse effects caused by the confluence between floors and then effectively improve the evacuation efficiency.