Blasting demolition is a widely preferred method for safe and efficient demolition of high-rise buildings. Due to the variation in the complexity of building structure, it is extremely important to study the dynamic characteristics of high-rise buildings subjected to controlled blast loadings for the effective design of blasting scheme. In general, blasting demolition involves two critical steps, namely, the development of crushed zones in the columns or walls and collapsing of the weakened structure. However, most studies on blasting demolition have focused majorly on the collapse of the weakened structure with little attention on the development of crushed zones in the columns. Currently, numerical simulations are widely used in the prediction of blasting results. However, the accuracy of the simulations results has raised a lot of questions considering that most engineers usually ignore the explosion of explosives and fracture of reinforced concrete columns mainly because they require a lot of time to model and simulate. Consequently, the blasting mechanism of reinforced concrete columns in controlled blasting demolition of raised buildings has not been fully explored despite the extensive research on blasting of reinforced concrete columns.
To this note, a group of Jianghan University researchers: Professor Jinshan Sun, Professor Yongsheng Jia, Professor Yingkang Yao and Professor Xianqi Xie conducted an experimental investigation of stress transient characteristics and failure mode of blasted reinforced concrete columns in the blasting demolition of buildings. In their approach, the authors blasted a 1000 mm by 700 mm by 4100 mm column in a 56-m-high frame structure demolished by controlled blasting technology. In particular, a new stress transient model for blasted reinforced concrete columns was proposed based on the collected data and experiment results. Finally, the proposed new model was validated by comparing the obtained results to the experimental results from field testing. Their research work is currently published in the journal, Engineering Structures.
The authors observed a multipeaked and jagged-triangular shaped explosion induced stress-time history curve because nonel detonators generally have longer time delay errors compared to the detonation time of the explosives in the blast holes. The bearing capacity of the blasted column gradually decreased after the detonation of the explosives. When it reduced to the initial axial compressive stress, however, the initial stress was released linearly to 0. Moreover, the residual column exhibited transient tensile stress under the push-pull movement of the concrete fragments due to the strong bending and extrusion of the longitudinal reinforcement bars. Furthermore, the proposed stress transient model agreed well with the experimental field-testing results thus confirming its feasibility for blasting demolition of high-rise buildings applications.
In summary, the study presented an investigation of transient stress characteristics of reinforced concrete columns under practical demolition blasting loading. Based on the experimental results, a new stress transient model for a detailed description of the stress state of blasted reinforced concrete columns in demolished high-rising buildings was proposed and successfully validated with experimental results from field testing. In a statement to Advances in Engineering, the authors noted that the proposed model has great potential of enhancing the accuracy of numerical simulations of blasting demolitions. Additionally, the study provides useful insights that would help future researchers to effectively determine the key parameters and monitor the adjacent columns for further verification of the proposed model.
Sun, J., Jia, Y., Yao, Y., & Xie, X. (2020). Experimental investigation of stress transients of blasted RC columns in the blasting demolition of buildings. Engineering Structures, 210, 110417.