# Black Loaded Columns--State of the Art Review
## 2 Experimental Testing
### Building Columns
Polyurethane bricks are lighter and have cheaper protection for columns but give three times worse results than steel jacketing. It is recommended to set bricks of higher density to improve the effect in the area of blast load. In [16], they also examined reinforced resin panels with insulation layers as a possible improvement of the column. This protection system gave the best results, minimizing column damage and the greatest deflection reduction. The protection system in the field test is shown in Figure 12. [PERSON] et al. [22], after their research on plain RC columns [14], tested RC columns covered with reinforced resin panels with an insulation layer and steel jacketing. From the obtained results, it can be concluded that a significant reduction in damage and displacement was achieved with the cladding system, but the spalling and burst of concrete cannot be prevented. Figure 14 shows a schematic representation of all specimens and their damage covered by the studies of [PERSON] et al. Figure 12: RC columns reinforced with: (**a**) polyurethane bricks [15; 16] and (**b**) resin panels and insulation layer [22]. Copyright permission obtained from authors. Figure 7:0 Comparison of damages of circular and square RC columns after the detonation of 1 kg of TNT: (**a**) front side and (**b**) back side [23]. Copyright permission obtained from authors. [PERSON] et al. [17] subjected four Ultra-High-Performance Fiber Reinforced Concrete (UH-PFRC) and four High Strength Reinforced Concrete (HSRC) square columns to the effects of blast loads. Columns were tested under varied charge weights from 1.4 kg to 48 kg of emulsion explosive (TNT equivalence factor is 1.4). The standoff distance was fixed at 1.5 m in all tests. Specimens were placed horizontally, and the axial load was applied using a pneumatic jack. The results showed that UHPFRC columns could better withstand overpressure and shock waves, reducing the maximum displacements. [PERSON] et al. [25] tested 10 Ultra-High-Performance Concrete (UHPC; six reinforced with twisted fiber and four reinforced with micro fiber) and 5 High Strength Reinforced Concrete (HSRC) columns. The length of the specimens was 2.5 m, and the cross-section was square with dimensions 0.2 m \(\times\) 0.2 m. In experiments, the standoff distances of the explosive from the columns were constantly 1.5 m in all tests, but the explosive weight was changed. For the UHPC columns, weights of 17.5, 25, and 35 kg, and for the HSRC 8, 17.5 and 25 kg were used. Residual load capacity tests showed that UHPC columns after blast loads did not lose much on the axial load capacity. UHCP columns also showed much better load capacity after 35 kg TNT detonation than HSRC columns after 8 kg TNT detonation. [PERSON] et al. [26] experimentally tested 12 columns at a scale of 1:4 under the blast load. They varied the void ratio, diameters, and thicknesses of the outer and inner steel tubes. The specimens' cross-section generally experienced denting, and that deformation helped to energy absorption from the overpressure from the near-contact explosions. The inner steel tube played the role of a dowel preventing direct shear failure, and this is the advantage of the CFDST columns over CFST and RC columns. On the tensile side of the column, the concrete was crushed, or horizontal flexure cracks appeared. [PERSON] et al. [27] tested three RC columns (30 cm \(\times\) 30 cm \(\times\) 375 cm) in full scale with the same material and geometrical properties on contact explosion at the bottom of the column. They used 0.1 kg of plastic explosive (PEK--TNT equivalent 1.15) and 0.5 kg and 1 kg of TNT. The TNT charge of 1 kg made a hole in the column; 0.5 kg destroyed the concrete cover, and the remaining core has no residual capacity; 115 g TNT equivalent caused the spalling  
Figure 7:1 Damage after blast load on RC members: (**a**) without protection; (**b**) with steel jacketing; (**c**) with polyurethane bricks, and (**d**) with reinforced resin panels [15, 16, 22]. Copyright permission obtained from authors.