Abstract: In the Chimney blasting demolition, field data shows that chimney is affected by the dynamic load effect in blasting instant. If the blasting cut angle is designed improper, it will affect the accuracy of the chimney dumping direction. Relies on the law of conservation of energy, the computational formula of the impact dynamic factor of chimney blasting is deduced, the dynamic stress of the remaining weak cross－section of the chimney blasting cut is studied .By theory calculating the value of the stress of the remaining part under the action of blasting impact load, comes to the higher limit of the cut angle which ensuring that the chimney would not sitting down. Engineering examples and field data are given to verify the correctness of the theory.

Key words: chimney, dynamic load effect, blasting demolition, impact dynamic factor, cut angle