受火后内置格构式钢管混凝土十字形截面型钢混凝土短柱轴压性能研究

Study on axial compression behavior of built-in lattice concrete-filled steel tube cruciform steel reinforced concrete short columns after fire

为研究受火后内置格构式钢管混凝土十字形截面型钢混凝土柱的轴压性能,开展1根未受火和6根受火后短柱轴心受压试验,得到荷载-轴向位移曲线,分析受火时间和受火面数量对短柱剩余承载力、延性、耗能和初始轴压刚度等的影响。引入受火后混凝土材料性能折减系数,结合相关规范提出内置格构式钢管混凝土十字形截面型钢混凝土短柱受火后承载力计算式。结果表明:受火与不受火短柱破坏模式基本相同,荷载-位移曲线划分为弹性段、弹塑性段、下降段和平缓段,最终发生斜向剪切破坏;随着受火面数量的增加,短柱的剩余承载力、延性和初始轴压刚度呈下降趋势;随受火时间增加,内置格构式钢管混凝土承担外荷载比例逐渐增大,荷载-轴向位移曲线逐渐呈扁平状,峰值位移、破坏位移滞后,短柱表现出良好的延性;提出的短柱承载力计算式结果与试验结果吻合良好。

To study the axial compression performance of built-in lattice concrete-filled steel tube cruciform steel reinforced concrete columns after fire,axial compression tests were carried out with one unfired short column and six short columns after fire to obtain load-axial displacement curves of and analyze the effects of fire duration and the number of surfaces exposed to fire on the residual bearing capacity,ductility,energy dissipation and initial axial compression stiffness of the tested short columns.By introducing the reduction factor of concrete material properties after fire,combined with the relevant codes,the calculation formula for the bearing capacity of built-in lattice concrete-filled steel tube cruciform steel reinforced concrete columns after fire was proposed.The test results show that the damage mode of the specimen subjected to fire is basically the same as that of the specimen not subjected to fire,experiencing four stages,i.e.,the elastic stage,elasto-plastic stage,descending stage,and the flat stage,and finally occurring the oblique shear damage.With the increase of the number of surfaces exposed to fire,the residual bearing capacity,ductility and initial axial compression stiffness of the short column show a decreasing trend.With the increase of the fire duration,the proportion of external load born by the built-in lattice concrete-filled steel tube gradually increases,the load-axial displacement curve is gradually flattened,the peak displacement and damage displacement lag.The short column shows good ductility.The theoretical calculation results are in good accordance with the test results.