Close-range Blast Response Prediction of Hollow Circular Concrete Columns with Varied Hollowness Ratio, Arrangement of Compression Steel, and Confining Stirrups’ Spacing

Blasts and accidental explosions are being reported more frequently than before with grievous injuries and loss of lives and damage to the structure, increasing the concern of disaster management authority officials. Structural engineers apprehend that such events may trigger progressive structural collapse leading to movable and immovable property losses and casualties, and therefore, the design of important load-carrying members such as columns is required to be improvised against blast loading. In this research work, a high-fidelity numerical model of 3000 mm long reinforced concrete (RC), 300 mm x 300 mm, solid square column provided with conventional transverse reinforcement carrying an axial working load of 950kN subjected to 82 kg-TNT explosive load at a scaled distance 1.0 m/kg 1/3 is developed in ABAQUS/Explicit-v.6.15 commercial software provided with Concrete Damage Plasticity (CDP) model with strain rate effects. The nonlinear behavior of compression steel re-bars and transverse stirrups are taken into account. Computational results corroborate the available experimental ones. To improvise the performance of the column, one solid circular RC column and hollow concrete columns (HCCs) equivalent to the solid square one with the same axial load but having circular lateral reinforcement have been considered. Available Codes of Practice guidelines for the design of reinforced cement concrete do not have any mention of the hollowness of the compression members for obvious reasons as these codes are meant not for their design against impulsive loadings (blast and impact). The effects of hollowness ratio, arrangement of the compression steel, and stirrups’ spacing are key studied design parameters in this numerical investigation. Results showed that a higher hollowness ratio with a single layer of reinforcement marginally decreases the peak displacement but produces a negative effect on the damage by exceeding its value that of the solid RC column. Configuration of the HCC column having 0.29 hollowness ratio with compression steel provided radially in two layers, more in the outer layer than in the inner one, connected with radial links and also tied with double circular transverse reinforcements at 150mm c/c exhibits the excellent blast performance in terms of peak displacement and damage. Besides, the HCC column having an angular deviation of 30 degree between the outer and inner layers of the steel bars performs better with regard to concrete crushi