| In recent years,in order to meet the needs of the development of building structure to the direction of long span and super high-rise,steel tube activated powder concrete structure has gradually become a research hotspot.As a basic composite structure,CFST structure has the advantages of high strength,strong seismic performance,and reactive powder concrete has the characteristics of high toughness,high tensile and compressive strength.In recent years,the incidence of fire is increasing worldwide.As one of the main load-bearing components of building structures,the fire resistance of columns will greatly affect the stability of buildings in fire,which may lead to structural instability or even collapse.Therefore,it is of great significance to study the fire resistance of steel tube active powder concrete column specimens.At present,the research of activated powder concrete column with square steel tube mainly focuses on the normal temperature,and the research of fire resistance at high temperature is less,which limits the popularization and application of this structure.In this paper,considering the influence of steel tube wall thickness(4 mm,6 mm,8 mm,10 mm),axial compression ratio(0.55,0.6,0.65),configuration of spiral stirrs and spacing(no configuration,spacing 60 mm,spacing 80mm),fire resistance tests were carried out on 8 square steel tube activated powder concrete column specimens at high temperature.Finite element simulation and theoretical analysis verification.The specific research content and main conclusions are as follows:(1)In order to investigate the fire resistance of activated powder concrete column with square steel tube,temperature rise test was carried out on 8 specimens under constant load,and the surface phenomenon and failure mode of each specimen after high temperature were analyzed.(2)The distribution of temperature field,axial displacement-time curve and fire resistance of each specimen were analyzed.According to the test data,the influences of wall thickness,axial compression ratio,configuration and spacing of spiral stirrups on fire resistance were studied.(3)By using ABAQUS finite element software,the numerical simulation of 8 square steel tube active powder concrete column specimens was carried out.The temperature field,failure mode,axial displacement-time curve of each specimen and the difference between the test value and the simulation value were analyzed and compared,and the reliability of the established finite element model was verified.(4)Based on the calculation method of equivalent compressive strength and limit analysis method of reactive powder concrete at high temperature,the calculation formula of ultimate bearing capacity of specimens at different times in high temperature was derived,and the theoretical fire resistance limit of specimens was calculated,which verified the feasibility of the calculation method.Main conclusions:(1)The oxide layer will gradually fall off after the surface of the steel tube is heated.The failure mode of the specimens without internal stirrup is shear slip failure,and the failure mode of the specimens with internal stirrup is waist drum failure.The smaller the wall thickness of the steel tube,the more obvious the buckling deformation of the specimen.(2)Each temperature measuring point of the specimen increases gradually with the increase of time and furnace temperature.The temperature rise rate of the measuring point near the steel pipe is faster,while the temperature rise rate of the measuring point inside the activated powder concrete is slower as the measuring point is deeper.The temperature rise of the inner test point of the specimen equipped with spiral stirrup is faster than that of the specimen without stirrup.(3)The fire resistance of the specimen increases gradually with the increase of steel tube wall thickness.Compared with the specimen with steel tube wall thickness of 4 mm,the fire resistance of the specimen increases by 10 min,4 min and 8 min with the increase of steel tube wall thickness by 2 mm,respectively.With the increase of axial compression ratio,the fire resistance limit of specimens decreases gradually.Compared with the specimens with axial compression ratio of 0.55,the fire resistance limit of specimens with axial compression ratio of0.60 decreases for 15 min,and that of specimens with axial compression ratio of 0.65 decreases for 26 min.The greater the axial compression ratio,the smaller the difference in fire resistance limit.The configuration of spiral stirrup has a great influence on the improvement of the fire resistance of the specimen.The fire resistance of the specimen equipped with spiral stirrup spacing of 80 mm is increased by 31 min compared with that without spiral stirrup,and the fire resistance of the specimen equipped with spiral stirrup spacing of 60 mm is increased by 35 min compared with that without spiral stirrup.It has little effect on improving the fire resistance of specimens.(4)After analyzing and sorting out the test data,the formulas for calculating the refractory limits of specimens under different factors are obtained by fitting.(5)By comparing the finite element simulation results with the temperature distribution of the section,the axial displacement-time curve and the fire resistance limit of the test,it can be seen that the error between the simulated values and the test values is small and the consistency is good,which can provide a reference for the fire resistance analysis of the steel tube activated powder concrete column under high temperature.(6)Based on the calculation method of equivalent compressive strength and limit analysis method of reactive powder concrete at high temperature,the calculation formula of ultimate bearing capacity of specimens at different times in high temperature was derived.The theoretical fire resistance limit of specimens was obtained by comparing the calculated results with the applied load in the test.It can be used to calculate the ultimate bearing capacity and fire resistance of activated powder concrete column of square steel tube during fire. |
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