Mechanical Analysis And Collapse Vibration Research Of Chimney By Directional Blasting

At present,directional controlled blasting is the safest,most economical and most efficient method to demolish RC chimneys.In order to ensure the accurate,stable and safe collapse of the chimney in the pre-designed direction after blasting,combined with engineering examples,the complex mechanical changes and collapse vibration effects during the directional blasting of chimneys are researched.(1)Based on the longitudinal force balance of the supporting part,a backward movement time-varying model of the neutral axis is derived.The model can better describe the backward movement law of the neutral axis.On this basis,the mechanical model of chimney directional dumping is established,and the mechanical changes during the chimney dumping are analyzed.(2)Aiming at the phenomenon of sitting down and aerial fracture during the chimney blasting demolition,corresponding mechanical models are established for analysis and discussion.The results show that the sitting down of the chimney's upper cylinder generally occurs after the blasting cut is formed.Reasonably reducing the cutting angle and height can effectively control the sitting down of the upper cylinder.During the dumping process,the cylinder will be broken in the air due to bending damage,especially the chimney with a height of more than 150 m,it is not easy to be damaged by shearing and cause aerial fracture.The higher the chimney height,the easier it is to break in the air first during the dumping process.(3)Aiming at the phenomenon of forward and back ward collapse during the chimney blasting demolition,corresponding mechanical models are established for analysis and discussion.The results show that the criterion one is more reasonable as the mechanical basis of chimney forward,and the calculation results of the chimney forward analysis theoretical model are conservative.The chimney back ward collapse with positive trapezoidal cut conforms to the theoretical model of chimney sliding,and the chimney back ward collapse with inverted trapezoidal or rectangular cut conforms to the theoretical model of chimney back ward collapse.Under the premise of ensuring that the chimney can be smoothly unstable and dumped,the cutting center angle can be reduced reasonably,which can effectively reduce the range of the chimney back ward collapse.(4)Analysis of the results of on-site vibration monitoring shows that the surface vibration effect induced by the continuous collapse and touchdown of the chimney is the most harmful to nearby buildings(structures).Therefore,using numerical simulations to study the effect of delay time,cutting shapes,cutting heights and angles on collapse vibration.The results show that increasing the delay time in the third zone can reduce the surface collapse vibration,but the delay time of the third zone should not be too long.It is suggested that the delay time of the second zone should be 100 ? 200 ms to control the collapse vibration best.The collapse vibration caused by the chimney collapse with positive trapezoidal blasting cut is greater than the collapse vibration caused by the chimney collapse with inverted trapezoidal blasting cut.Reducing the cutting height or cutting angle can significantly reduce the chimney collapse vibration.However,the method of reducing the blasting cutting angle is more obvious than the method of reducing the cutting height for the damping effect.