Experimental Study On Fire Resistance Of Concrete Filled Circular Steel Tubular Columns With Earthquake Damage

Secondary fires after the earthquake are a common disaster and pose a great threat to the safety of the engineering structure.Although the conventional circular steel tube concrete structure with fireproof coating usually has good fire resistance,the fire resistance behavior of the circular steel tube concrete structure after the damage is significantly deteriorated.Therefore,based on the large-scale circular steel tubular concrete double-column specimens,the quasi-static test,open flame test and other research methods are used to investigate the fire resistance of the shock-damping circular steel tubular concrete columns.The main research and conclusions of this paper mainly include:1.The quasi-static test of six circular steel tubular concrete double-column specimens with fire-retardant coatings was carried out,revealing the effect of the double column test piece column end fireproof coating caused by the maximum interlayer displacement angle,axial compression ratio,fire retardant coating thickness,whether to use steel mesh reinforcement fireproof coating and other parameters.Based on the analysis of the crack initiation and peeling of the double-column specimens at the end of the test,the development law of the cracks and the spalling model of the column end fireproof coating with the damaged circular steel tube concrete double columns were preliminarily established.The research shows that:(1)the thicker the fire retardant coating layer,the increased number of cracks and flaking and the increase of the maximum crack width and the maximum flaking length,and the more serious the damage;(2)with the use of steel mesh to reinforce the fire retardant coating layer,the crack development rate slows down,the maximum peeling length becomes smaller,and the maximum width of the crack becomes larger;(3)The unloading and reloading process of the damaged specimen in the in-situ state has a serious influence on the displacement in the severe direction of the damage.2.The open flame test of six seismically damaged circular steel tubular double-column specimens and one undamaged comparative specimen was carried out,analyzing the characteristics of the temperature field of the column end section of the seismic damage specimen,and reveals the influence of parameters such as maximum interlayer displacement angle,axial compression ratio,fire retardant coating thickness,and steel mesh reinforcement on the fire resistance of seismically damaged circular steel tubular double-column specimens.The research shows that:(1)When the strip end fireproof coating is severely peeled off,the rate of heat transfer from the outside to the inside of the plastic hinge area is accelerated;Under high temperature,the damage area of the circular steel tubular double-column specimen with severe seismic damage will be transferred from the vicinity of the column to the plastic hinge area of the column end;(2)With the increase of the maximum inter-layer displacement Angle,the fireproof limit of the specimen decreases seriously,and the maximum axial expansion decreases linearly;(3)With the increase of coating thickness,the fireproof limit decreased by 26.8%,and the maximum axial deformation is also reduced by 1 time;(4)The fireproof coating layer of steel wire mesh reinforcement improves the fire resistance limit of the test piece by 151.9%,prolonging the high temperature expansion time of the core concrete in the column,and nearly doubled the axial deformation..