Study on Selection of Blasting Incision Angle of Ultra-high Reinforced Concrete Chimney

The reasonable selection of the incision angle is an important factor for the success of blasting demolition of a typical reinforced concrete chimney. In order to determine the selection range of incision angle, the isolation method was adopted to establish a theoretical model according to the force and failure characteristics of the residual section. The solution formula of any angle position on the residual section was derived, and a revision coefficient k was defined to express the influence of the cylinder at the upper part of the unnotched section. Furthermore, the stress and bending moment conditions of the dumping cylinder were established, and the selection range of the incision angle was obtained by combining the solution formula and the damping conditions. The case study shows that with the increase of the incision angle, the maximum tensile stress, the maximum compressive stress and the bending moment generated by the upper cylinder of the incision tend to increase, while the resistance moment of the residual section tends to decrease. The upper limit of the selection of the incision angle can be obtained when the maximum tensile stress reaches to the material strength limit, and the lower limit can be determined when the two bending moments are equal. Changing the incision angle would have a greater effect on stress than changing the incision height. Under the condition that the actual incision height is 4.5 m in the engineering case, the selection range of incision angle based on the established theoretical model is 198°~237.6°, and the actual incision angle is 216° within the theoretical selection range, which further verifies the reliability of the theoretical model. More extensive application and guide engineering practice are expected.