| Partially encased composite steel and concrete columns,referred to as PEC columns,is a new type of composite columns consisting of welded H-shaped steel section and concrete casted between the flanges.It has good ductility,bearing performance and economic performance,and is suitable for prefabricated buildings and urban renewal building.In order to improve the construction efficiency of the prefabricated PEC structural system,light-weight aggregate concrete is introduced into the PEC column to form partially encased composite steel and light-weight aggregate concrete columns,referred to as PELC columns.Due to the exposed steel flanges of PELC column,fire protection must be carried out.However,the researches on PEC columns are mainly focus on the performance under normal temperature,while the experimental and theoretical researches related to fire resistance are relatively lacking,especially for the research on fire protection of PEC columns.In order to learn the failure mode,temperature distribution and fire resistance of PELC columns under fire,this paper studied the fire resistance performance of PELC columns and the fire protection effect of coatings.The main research contents are as follows:(1)18 steel plates coated with fire-retardant coatings were tested under ISO 834 standard heating conditions,and the temperature-time relationship curves of the components and furnace were obtained.Then,the thermal conductivity of intumescent and non-intumescent fire-retardant coatings with different thicknesses were obtained.The influence of types,thicknesses and temperatures on thermal conductivity of fire-retardant coatings were analyzed.It was found that the thermal conductivity of the fire-retardant coating decreased with the increase of the coating thickness,and the fire performance of the intumescent fireproof coating is obviously better than that of the non-intumescent coating fireproof coating.(2)One axially-compressed full-scale PEC column and five axially-compressed fullscale PELC columns were tested under ISO 834 standard heating conditions.The temperature of key measuring points,the fire resistance limit of specimens,the axial displacements-time relationship curves,the lateral deformation-time relationship curves and the typical failure mode were obtained.At the same time,the influence of the load ratio,concrete types and fire-retardant coatings on the fire resistance were studied.(3)The temperature field models of the PELC columns under ISO 834 standard heating conditions were established using ABAQUS,and their reliability were verified by the measured temperature data in this paper.The influences of section sizes,concrete types,heating time,fire conditions and thicknesses of fire-resistant coating on the temperature distribution of the PELC columns under fire condition were studied.And the heating process of the PELC column was analyzed in detail.(4)The thermodynamic models of PELC columns under ISO 834 standard heating conditions were established using ABAQUS,and their reliability were verified by the actual test data in this paper.The influences of load ratio,slenderness ratio,section size,concrete compressive strength,and thickness of fire-retardant coatings on fire resistance of PELC columns were studied.And the whole process of the PELC column under fire was analyzed in detail.(5)A simplified equation was regressed based on the parametric analyses to predict the fire resistance of PELC column subjected to the ISO 834 standard heating condition on four sides considering the influence of fire-retardant coating.At the same time,the influences of section size,slenderness ratio,and fire exposure time on the bearing capacity coefficient of PELC columns were studied,and an equation is regressed based on the parameter analysis to predict the bearing capacity influence coefficient,then the calculation method of bearing capacity of PELC columns at high temperature was obtained. |
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