# Black Loaded Columns--State of the Art Review
## 2 Experimental Testing
### Building Columns
of the concrete cover. Column damage profiles are shown in Figure 7:2 A contact explosion causes significant local damage on at least three sides of the column, while a far-field explosion causes the worst damage on the front, exposed side. [PERSON] et al. [28] investigated the same blast load scenario on the column concerning the increase in the cross-sectional width of the column. They experimentally tested columns of dimensions 50 cm \(\times\) 30 cm, 70 cm \(\times\) 30 cm, and 90 cm \(\times\) 30 cm. Rectangular columns showed better behavior under contact explosion than squares. They examined the residual load-bearing capacity of the column and determined the column damage index. When the width dimension of the column subjected to the blast load is greater two and more times from depth, the damage index is lower. [PERSON] et al. [30] examined five half-scale RC columns. Three columns are strengthened with unidirectional and woven CFRP laminates while the other two remained unprotected. They were first tested in the shock tube on the induced blast load, and thereafter, their residual axial capacity was examined. The column strengthened with CFRP laminates with \(\pm\)45\({}^{\circ}\) woven fibers showed the best blast behavior and the most ductile response. [PERSON] and [PERSON] [43] investigated how longitudinal and shear reinforcement ratios, concrete strength, and the number of explosives affect the demolition of RC building columns. Their primary research goal is not terrorist attacks but the demolition of diligidated concrete buildings. They used a Composite 4 (C4) explosive because of its stability and ease of shaping and placed it in the core of the column. They found that shear reinforcement plays a significant role in the residual bearing capacity after blasting; the strength of the concrete also affects the increase in residual compressive and flexural resistance capacities. The quantities of explosives and reinforcement cannot be applied to the external action of the explosion, but certainly, conclusions about the role of reinforcement and the strength of concrete are useful. [PERSON] et al. [44] observed two scenarios: first is a contact explosion with the amount of PETN that fits in the suitcase, and the second is the close-in scenario when the explosive is in the vehicle. They investigated the impact on RC columns and strengthened columns. Polymer concrete, SIFCON (Slurry Infiltrated Fiber Concrete), DUCON (Ductile Concrete), and Ultra-High-Performance Concrete (UHPC) were used to improve the resistance of the bridge and building columns. The appearances of column damages after contact explosion and the residual load capacities are shown in Figure 7:3 The results showed an increase in residual bearing capacity by up to 70%. Figure 7:4 Column damages after blast loads: (a) 1 kg; (b) 0.5 kg and (c) 115 g TNT [27]. Copyright permission obtained from authors. [PERSON] et al. [45] tested five columns in an explosion containment vessel (ECV). The columns were exposed to an explosion of 40 g charge mass, and the distance of the explosive was changed in each test from a contact explosion to a standoff distance of 50 cm. They installed four smart aggregates (SAs) in each specimen for internal damage detection, shown in Figure 7:5 The propagation of the stress wave energy decreases with the formation of cracks under the blast load, and hence the amplitude of the time-domain signal recorded by piezometric smart aggregate sensors decreases with the appearance of cracks. This method of detecting internal damage has proven to be useful for completing the picture of the condition of the structure because internal cracks have a greater impact on the damage index of the structure than surface cracks. [PERSON] and [PERSON] [31] examined columns measuring 100 mm \(\times\) 100 mm \(\times\) 1000 mm on the action of a different amount of explosion placed at a vertical standoff distance of 300 mm.