Application of controlled blasting demolition technology in ultra-high coaxial thin-walled steel inner cylinder reinforced concrete chimney

To achieve the goal of 'carbon neutrality', it is of great significance to accelerate the process of dismantling high-carbon and high-pollution thin-walled cylinder structures such as chimneys and so on. A 183 m ultra-high coaxial thin-walled steel-inner-cylinder reinforced concrete chimney (UCTS-RCC) was successfully demolished for the first time. To successfully dismantle the UCTS-RCC by controlled blasting demolition technology, the necessary structural mechanics theoretical analysis and the critical blasting designs rationality verification were carried out. Based on the equilibrium equation of force and bending moment, a theoretical model of incision angle selection was established to determine the incision design of the steel inner cylinder (SIC). The stability of SIC under the designed incision parameters was verified based on FEM statics analysis. The cutting experimental on the target steel plate was completed with a linear shaped cutter to obtain the cutting effect. The cutting process and the overall collapse process of the UCTS-RCC were simulated by LS-DYNA. Based on the fixed axis rotation differential equation, the synchronous toppling theoretical model were established to study the motion of the UCTS-RCC. The results showed that the maximum stress at the position of the directional window and the stresses of the remaining supports were less than the yield limit of Q235B steel after that several pretreatment windows were carried out, the SIC could maintain the stability of remaining structures. The cutting experimental results of the target steel plate using linear shaped cutter were basically consistent with the cutting simulation and the cutting effect satisfied the design requirements of instantaneous cutting separation of the supports. According to the obvious difference of material properties between Q235B steel and reinforced concrete, the ignition delay time of the SIC was set 2 s earlier than that of the RCC. According to the synchronous collapse simulations, it could be known that the ignition delay time setting was reasonable and the collapse motion state of the UCTS-RCC was approximately fixed axis rotation, which was in line with the established synchronous toppling theory model. The SIC and RCC finally successfully collapsed synchronously. The blasting scheme and the rationality verification methods were applied successfully in this project, which was of great significance to provide a reliable reference for such ultra-high thin-walled cylinder complex structural chimney.