Experiental Study On Fire Safety Of Steel Frame Structure In Rural Buildings

Building fire is one of the disasters with high frequency and serious hazards.Both the incidence and the resulting mortality and property losses of fires in rural areas have always been high.High temperature has a significant adverse effect on the mechanical properties of structural steel,and it is believed that steel will lose its full strength in an environment exceeding 700°C.Based on all researches at home and abroad,fire protection design methods have been proposed for steel structures.However,the existing researches have not been fully verified on the mechanical properties of steel frame structures under real fire.The current code’s approach to fire protection design for steel structures is still lacking in practical application.Therefore,it has theoretical significance and engineering application value to carry out the research on fire safety of steel frame structures in rural buildings.In this paper,an experimental study on fire safety of steel frame structures in rural buildings is carried out.Through five full-scale steel frame structure fire tests,temperature distribution and mechanical response of steel frame structures under different fire conditions are obtained.The fire conditions contains ISO834 standard curve heating,residential fire heating,warehouse fire heating and heating without fire protection.The fire resistance of steel frame structures is further clarified through comparative analysis.Based on existing experimental results and specified fire protection design methods,the specific fire protection design suggestions are put forward.The main research work is as follows:(1)Based on the layout and stress characteristics of rural buildings,a complete fire test scheme of steel frame structure is designed and implemented.Considering the force of the building,the size and external load of the test piece,the corresponding heating scheme and the response monitoring schemes was selected,In order to ensure the safety of the test,the structures such as ground beam,external steel cable system and support column are designed to prevent structural overturning and failure of the test column.(2)By analyzing the air temperature change in the test,the real fire temperature distribution law of the villages and towns is obtained.Compare the actual fire temperature rise curve of villages and towns with the standard one to explore the difference between the maximum temperature and temperature change.For residential and warehouse fires,the maximum air temperature is only 62.8% and 85.3% of the standard heating curve,and the fire develops rapidly.The heating time does not exceed 85 min,and then enters the rapid cooling stage immediately.(3)Summarize the changing rules of stress and deformation of fire-bearing members during the whole test process,and define the fire response mechanism of steel frame structural members.According to the determination,the fire of steel frame structural members can be judged as three stages: expansion,compression,cooling and contraction.By analyzing the temperature distribution,deformation law and failure mechanism of components in each stage,it is found that the deformation of components is effectively restrained due to the overall restraint of structure and the redistribution of internal force.The fire resistance limit is increased by more than26%,and the fire resistance is obviously due to the independent components.Based on the temperature and strain distribution of non-fire members and their variation rules,the fire impact range of steel frame structure is determined as the interval formed by adjacent non-fire joints.(4)Evaluate the fire safety performance of steel frame structure in rural buildings according to the test phenomena and reflection rules,and put forward fire protection design suggestions for steel frame structure.According to the comparison of the maximum deformation generated during the fire process and the bearing limit value,it is found that the steel frame structure of rural buildings has better fire resistance and has large safety redundancy in the corresponding fire conditions.Summarize the methods and conclusions of existing fire resistance tests for structural members at home and abroad,define the current fire protection design methods for steel frame structures in China,and combine with the analysis of test conclusions,draw a conclusion that the current fire protection design methods are inadequate.In terms of fire resistance grade,fire conditions,checking objects and methods,Adverse load selection and fire safety performance of structures are proposed for fire protection design of steel frame structures in rural buildings.