Multi-Risk Analysis Of Lagre Space Steel Structure Building Based On Fire Randomness

Large space steel structure building is more and more widely used in the new architectural,such as super market,convention and exhibition center,stadium,high-speed railway station.It has the characteristics of large scale,wide area,high space,special structure and dense personnel,which puts forward new requirements for fire prevention and rescue.In this paper,available safe egress time and required safe egress time are introduced to measure fire risk.The available safe evacuation time is the time when the environment inside the building reaches the point where people cannot survive after the fire happens.Survival threats mainly include high temperature thermal damage,physiological toxicity of smoke and mechanical injury caused by building collapse.Required safe egress time is the time from the start of a fire when people flee to a safe area,mainly including fire alarm time,pre-action time and evacuation action time three parts.Based on the heat fluent and material fluent in fire in the process of fire,the smoke filling model,smoke temperature rise model and steel structure temperature rise model are established in this paper.Then the reliability of the theory is verified through full-size experiment,heat transfer experiment of steel structure and coupling simulation of FDS,Matlab and Fluent.Four experiments and nine simulations show that the average error of theoretical and experimental values of smoke temperature rise is 14.51%,the average error of smoke filling is 12.55%,and the average error of steel component temperature rise is 18.67%.Based on the behavior characteristics and building characteristics of evacuation in fire,the model of required safe egress time must be established,which includes fire alarm time model,pre-action time model and evacuation action time model.After that,the Pathfinder software was used to simulate the evacuation process,and the average error between the theoretical value and the simulated value was 9.59%.This indicates that the above model can be used to evaluate fire risk,but the occurrence,development of fire and the evacuation process are both deterministic and random.On the one hand,it follows the fire theory and statistical law,on the other hand,it is affected by many uncertain parameters.In this paper,the fire growth rate and burned area are taken as random parameters and input into the fire risk assessment model.Through Maltab software,Latin hypercube sampling method is used to establish the random model under the influence of single risk and multiple risk factors in the fire.The sampling results show that: considering only the single risk effect,the probability of building casualties caused by smoke filling is 17.75%,the probability of building casualties caused by high temperature is 12.04%,and the probability of building casualties caused by structural collapse is 2.54%.Considering the impact of multiple risks,the probability of casualties in the building is 18.13%.According to the independent analysis of each individual evacuation process in the building,the probability of all casualties in the building is 3.97%,and the random risk distribution function is established based on the sampling results.