Study On Rapid Assessment Method Of Building Ruins Rescue Safety Under Aftershock

The damage and collapse of buildings were the main causes of casualties in the earthquake.In the earthquake rescue,aftershocks caused the ruins of the secondary collapse will threaten the safety of rescuers and trapped people.In order to ensure the life safety of rescue workers and trapped people,assessing the living space in the ruins body is an essential part of earthquake rescue.At present,China does not give relevant standards and norms for the safety assessment of earthquake rescue sites in ruins,and the evaluation results are very dependent on the discipline background,work experience,cognitive differences and the physical and psychological conditions of the field commanders at that time.In the earthquake rescue site "time is life",determining an accurate and reasonable debris safety rapid assessment criterion is of great significance to improve the rescue efficiency.Therefore,in view of the urgent need of ruins safety assessment in earthquake rescue,this paper starts the following parts of work:1.Collect 100 groups of main aftershocks of magnitude 6 or above in mainland China from January 1966 to December 2021,and divided into 4 groups of 6.0-6.4,6.5-6.9,7.0-7.4 and 7.5;including 1118 aftershocks of magnitude 4 or above,which were divided into 8 groups of 4.0-4.4,4.5-4.9,5.0-5.4,5.5-5.9,6.0-6.4,6.5-6.9,7.0-7.4 and7.5 according to the magnitude.According to the rescue survival rate of emergency rescue period is divided into 12 hours,24 hours,48 hours,72 hours,96 hours,120 hours,144 hours and 168 hours(7 days)after the earthquake,to the above collected the main aftershocks record time statistics,get the biggest aftershocks and the main magnitude experience relationship formula,the maximum aftershocks in the probability and different magnitude of strong aftershocks.2.Analyzed the actual earthquake damage cases,summarized the main forms of collapse of the buildings,analyzed their stress characteristics,divided the typical building ruins with living space into four types: stacked cake,inclined,V-shaped collapse and suspension collapse,condensed the corresponding simplified mechanical analysis model,and obtained the PGA formula of critical collapse.3.Based on the established debris body simplified mechanical analysis model and critical collapse PGA discrimination criteria of combining debris body safety assessment method,gives the living space damage state of critical collapse PGA estimates and critical collapse magnitude,considering the magnitude aftershocks in different period of probability,gives all kinds of typical building ruins under the action of aftershock the probability of secondary collapse.4.Numerical simulation analysis was used to evaluate the safety of four typical living space under the influence of aftershocks in building debris.The comparative analysis results with the safety evaluation results based on the simplified mechanical analysis model show that the difference in the probability of secondary collapse obtained by the two methods is small,between 3.57% and 21.43%,which verifies the rationality of the simplified mechanical model and the PGA classification formula proposed in this paper,which can be used for the safety assessment of earthquake rescue site.