钢筋混凝土轴压圆柱耐火性能的尺寸效应

Size effect on fire resistance performance of reinforced concrete circular columns under axial compression

为研究钢筋混凝土缩尺模型柱与足尺原型柱耐火性能的关系,对几何相似的若干不同尺寸钢筋混凝土圆柱开展了明火试验和有限元分析,考察轴压比、体积配箍率、纵筋配筋率和升温条件等因素对柱耐火性能尺寸效应的影响,分析不同缩尺比柱的受火时间等效关系及热力响应相似性。结果表明:截面尺寸越大,随轴压比增加,钢筋混凝土柱的高温爆裂越严重;箍筋间距减小会加剧混凝土的爆裂程度,从而削弱混凝土柱的耐火性能;随轴压比增大、纵筋配筋率减小,柱的耐火极限降低,且轴压比和配筋率对大尺寸柱耐火性能的影响更显著;小尺寸柱的耐火性能受升温条件影响较大,但大尺寸柱的耐火性能对升温条件变化较为不敏感;在ISO 834标准升温条件下,当柱轴压比不超过0.4、混凝土高温爆裂不明显时,不同缩尺比柱受火时间服从缩尺比的1.46次幂的等效关系,在该关系下不同缩尺比柱的纵筋温度发展、截面平均温度发展、轴向变形发展以及耐火极限均呈现良好的相似性;而当混凝土高温爆裂较为严重、轴压比超过0.4,或升温条件为非标准升温时,采用小尺寸柱的耐火极限及该时间等效关系预测大尺寸柱耐火极限可能偏于不安全。

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 O.4,or the heat-rising curve is not the standard temperature-time curve.