受火冷却后钢管混凝土叠合短柱的轴压力学性能

Axially Loaded of Concrete-Encased Concrete Filled Steel Tubular Stub Columns after Fire

为掌握受火冷却后钢管混凝土叠合短柱的轴压破坏机理和力学性能,基于试验研究和有限元模拟,分析了叠合短柱的破坏模式、轴压极限承载力和轴向刚度.考虑截面形状、钢管尺寸和长细比3个参数的变化,完成了8根叠合短柱在ISO-834升温曲线作用下的受火试验和受火冷却后的轴压承载力试验,并采用ABAQUS进行了非线性有限元模拟.研究结果表明:与钢筋混凝土短柱相似,受火冷却后叠合短柱的破坏模式为受压破坏;与常温时相比,受火180 min冷却后,叠合短柱的轴压极限承载力下降27.4%~38.2%,轴向刚度下降61.4%~69.0%;当受火时间和钢管尺寸均相同时,钢管外部钢筋混凝土结构层增大1.53倍厚度,受火冷却后圆形叠合短柱的轴压承载力和轴向刚度降幅分别下降8.4%和1.3%,方形叠合短柱的轴压承载力和轴向刚度降幅分别下降5.8%和4.1%;与模拟值相比,提出的简化计算方法计算的轴压极限承载力偏差的平均值和标准差分别为4.9%和5.3,计算的轴向刚度偏差的平均值和标准差分别为13.8%和9.8.

In order to investigate the failure mechanism and structural performance of axially loaded concrete-encased concrete filled steel tubular （ C F S T ） stub columns after fire exposure, the failure mode, axial compression ultimate bearing capacity and axial stiffness of concrete-encased CF S T stub columns were analyzed based on experimental study and finite element model （ F E M ） simulation. A total of 8 concrete-encased CFST stub columns specimens with different cross-section types, steel tube dimension and slenderness ratios were tested after fire exposure, and the nonlinear FEM simulation was carried out by ABAQUS software. T he results show that compressive failure modes are observed for concrete-encased CFST stub columns, which is similar to reinforced concrete stub columns. Compared to a specimen at ambient temperature, the drop of axial compression ultimate bearing capacity of concrete-encased CFST stub columns is about 27. 4% - 38. 2% , and the drop of stiffness is about 61.4% -69. 0% . When the fire exposure time and the size of the specimens are the same, and the thickness of the reinforced concrete cover improve to 1. 53 times, the rate of decline of axialcompression ultimate bearing capacity and axial stiffness for circular specimens are 8 . 4 % and 1 . 3 % ,respectively, and for the square specimens, the rate of decline of axial compression ultimate bearing capacity and axial stiffness are 5. 8 % and 4. 1 % , respectively. Compared with the FEM simulation results, the mean and standard deviation of simplified method of calculation error are 4 . 9 % and 5. 3 for axial compression ultimate bearing capacity, the mean and standard deviation of axial stiffness calculation error are 13. 8% and 9.8.