钢筋混凝土烟囱爆破拆除的下坐及早期断裂预测

为分析钢筋混凝土烟囱在爆破拆除时发生下坐与空中断裂现象的机制并对其进行预测，对一高180 m烟囱的下坐和空中断裂过程进行了观测和分析。基于混凝土的压缩全应力-应变曲线特征，分析了烟囱支撑区的破坏过程，构建了烟囱失稳下坐的判别模型。通过建立烟囱下坐冲击作用下爆破切口以上烟囱的动力响应模型，分析了下坐冲击附加动应变波在烟囱中的传播特征。研究结果表明，考虑混凝土全应力-应变曲线特征和支撑区横截面应力和应变分布特征时，倾覆力矩与抵抗力矩的比值f可作为失稳下坐的判别条件之一；烟囱发生下坐的必要条件是支撑区最小残余承载力小于烟囱的重量。烟囱在下坐结束阶段，获得一定初速度的烟囱冲击基础时将产生冲击荷载，并在烟囱中部引起大于底端应变的应变，即产生动应变高程放大效应，该效应是导致烟囱发生早期断裂的主要原因。烟囱越高，下坐冲击历时越短，动应变高程放大效应越显著，发生断裂的风险也越大。随着烟囱高度的增加，烟囱最危险截面的位置也越高:由烟囱中下部移至烟囱中上部。

Prediction of sinking down and early break in the air of reinforced concrete chimney during blasting demolition

The collapse of the support part and break in the air of the reinforced concrete chimney during blasting demolition seriously affect engineering safety. Monitoring and analysis of a 180m chimney demolition were carried out to analyze the mechanism of these phenomena and distinguish them. Based on the characteristics of the stress-strain curve of concrete, the progressive failure process of the support part is analyzed. The static equilibrium equation of the cross-section is constructed, and the discrimination model for the instability and support part collapse of the chimney is proposed. By establishing the dynamic response model of the chimney above the blasting notch under the bottom impact, the propagation characteristics of the stress wave in the chimney are analyzed. The results show that the ratio of gravity moment to resisting moment can be used as a criterion of instability determination, considering the distribution characteristics of stress and strain in the cross-section of the support part. The compression failure of the concrete in the support part is almost inevitable under large eccentric compression. The necessary condition to prevent support part collapse of the chimney is that the minimum residual bearing capacity of the support part is not less than the weight of the chimney. When the chimney with a certain initial velocity impacts the foundation at the end of the support part collapse, an impact load will be generated and cause the strain in the middle of the chimney greater than the strain at the bottom. The elevation amplification effect of dynamic strain is an important reason for the chimney breaking in the air. The higher the chimney is, the shorter the impact duration is, and the more significant the dynamic strain elevation amplification effect is. As the height increases, the position of the most dangerous section of the chimney will move from the middle and lower to the middle and upper.