Size effect on fire resistance performance of reinforced concrete circular columns under axial compression
The fire tests and finite element analysis were carried out on reinforced concrete circular columns with proportional geometric dimensions to study the size effect on fire resistance of reinforced concrete circular columns under axial compression.The influences of axial compression ratio,volume stirrup ratio,longitudinal reinforcement ratio and heating conditions on the size effect of fire resistance of columns were investigated.The equivalent relationship of the fire duration and the similarity of thermal-mechanical responses of columns with different scales were explored.The results show that the larger the section sizes or the higher the axial compression ratio,the more severe the fire-induced concrete spalling on the columns.A decrease in the stirrup spacing may aggravate the spalling degree,thus weakening the fire resistance of concrete columns.With an increase in the axial compression ratio or a decrease in the longitudinal reinforcement ratio,the fire resistance of columns decreases.In particular,the influence of the axial compression ratio and reinforcement ratio on large-scale columns is more significant.The fire resistance of small-scale columns is greatly affected by the heating conditions,but that of large-scale columns is not sensitive to the change of heating conditions.In ISO 834 standard fire,the fire duration of columns with different scales follows the equivalent relationship of the 1.46 power of the size scale ratio,when the axial compression ratio is less than 0.4 and the concrete spalling is not significant.Under this equivalent relationship,the temperature evolution of longitudinal reinforcement,the average sectional temperature variation,the development of axial deformation and the fire resistance of columns with different scales exhibit good similarity.However,the fire resistance of a large-scale column predicted by that of a small-scale column and the time equivalent relationship may be higher than the real value,when the concrete spalling is severe,or the axial compression ratio exceeds 0.4,or the heat-rising curve is not the standard temperature-time curve.
reinforced concrete circular columnfire testfinite element simulationfire resistancesize effect
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