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

Abstract

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.