Experimental investigation of stress transients of blasted RC columns in the blasting demolition of buildings

Blasting demolition is the preferred method for safely and efficiently demolishing high-rise buildings, and numerical simulation is very helpful for the design of complicated blasting schemes. In simulations of demolition projects, the explosion processes and blast loadings are usually ignored to save computer time. However, the stress transients of blasted columns at the bottom of buildings are important boundary conditions, which may affect the accuracy of simulation results. Yet, few works have investigated it and provided a detailed model. To investigate the features of stress transients of reinforced concrete (RC) columns, an experiment was conducted in the present study. In a 56-m-high frame structure demolished by controlled blasting technology, a 1000 mm x 700 mm x 4100 mm column was blasted. The collected data include strain-time histories and failure mode of the column. The study shows that explosion-induced stress-time history curves far from the blastholes are jagged-triangular, which may have multiple peaks because of the delay time errors of detonators. After detonation of explosives, the bearing capacity of the column gradually decreases, which takes several milliseconds. When the bearing capacity reduces to less than the initial axial compressive stress in the column, the initial stress releases linearly, which also takes several milliseconds. The movements of the concrete fragments bent the longitudinal reinforcement bars, which induces a strong tensile stress in the residual column; their stress-time history curves are triangular. Based on the experiment results, a stress transient concept model is proposed to detailly describe the stress state of blasted RC columns in demolished high-rising buildings, which can be applied in the numerical simulation of demolition blasting.