Performance Based Fire Resistance Design Of Steel Frames Under Post-earthquake Fire

Under the action of earthquake,the integrity of steel structure will be damaged.In case of post-earthquake fire,due to the poor fire resistance of steel,the probability of further damage and even collapse of steel structure will increase significantly.At present,the main research directions of post-earthquake fire include the fire resistance of building structures,the probability model of post-earthquake fire by using the existing post-earthquake fire data,and the risk assessment of post-earthquake fire.At home and abroad,the research on the vulnerability of structures under earthquake and wind load has been more in-depth,while the research on the vulnerability of structures under local fire or post-earthquake fire is relatively few.Therefore,it is of great significance to study the vulnerability of steel structures under post-earthquake fire,which can provide research reference for structural damage assessment under post-earthquake fire.In this paper,the fire vulnerability of three story and three span plane steel frame after earthquake damage is studied.The main research contents are as follows:(1)The basic knowledge and theory of heat transfer are briefly described.The thermal and thermodynamic parameters of steel and fire retardant coatings are selected and applied to the post-earthquake fire analysis of the whole frame,and the temperature field and thermal coupling analysis results of the whole frame under the action of post-earthquake fire are obtained.(2)In this paper,the fire load density is selected as the fire intensity index and the fire resistance limit as the failure state index to divide the different performance levels of the structure,and the calculation samples are determined by Latin hypercube sampling.The multi-storey and high-rise integral frame model is established by ABAQUS,and the post-earthquake fire vulnerability analysis of multi-storey and high-rise steel frame based on fire load density is carried out considering the fire condition at the bottom of the frame.The results show that the probability of steel frame failure increases with the increase of fire load density;Under the frequent,fortified and rare earthquakes of El Centro wave,the probability of different damage of 9-story steel frame is significantly higher than that of3-story steel frame.(3)Considering the fire condition of the bottom layer of the frame,the fire resistance limit and vulnerability of multi-storey steel frame structure under the action of post-earthquake fire under different influencing factors are studied by selecting the ground motion records of different strength,different load ratio and different thickness of fire retardant coating,and the vulnerability curve results are compared.The results show that the probability of different failure of steel frame under El Centro wave is significantly higher than that of the other seven seismic waves;The fire endurance time of steel frame decreases with the increase of load ratio,and the exceedance probability of steel frame failure increases;After the fire protection of the fire components,the fire endurance time of the steel frame is significantly improved,and the probability of different degrees of damage of the steel frame decreases with the increase of the thickness of the fire retardant coating.(4)By changing the fire position of steel frame,such as single column fire,single beam fire,local single room fire,two room fire,single span fire and multi span fire,the post-earthquake fire vulnerability of multi-storey steel frame under different fire conditions is studied.The results show that the probability of different degrees of failure of multi-storey steel frames under different fire locations increases with the increase of fire load density;With the expansion of fire area,the probability of different failure of steel frame increases;Under similar working conditions such as single beam and single column under fire,the probability of different degrees of failure of steel frame varies slightly.