# Black Loaded Columns--State of the Art Review
## 2 Experimental Testing
### Bridge Columns
In the C category (\(Z\leq 0.6\) m/kg\({}^{1/3}\)), columns are exposed to the higher loads than columns in A (\(Z>1.2\) m/kg\({}^{1/3}\)) and B (\(0.6<Z\leq 1.2\) m/kg\({}^{1/3}\)). Figure 2: CFST column—details of column-to-foundation beam connection [7]. [PERSON] et al., in Part II [35], provided a review of experiments represented in Part I [4]. Square columns experienced greater net resultant impulse than circular columns under the same blast loads and also had a larger cross-section area, so less shear occurred at the base. To increase the shear capacity of the column at the base and the ductility, it is necessary to increase the amount of transverse reinforcement. Moreover, columns with continuous spirals had a better performance than columns with discrete ties, which confirms the recommendation given in [8]. Due to changes in column design, the weight of charge, and standoff distance, several levels of damage were obtained [37; 38]. The test setup is shown in Figure 4. Superficial damage means that the column performed well and has only surface damage and cracks, while minor damage means spalling of the concrete cover and cracks along the column. Deformations, flexural cracking, and spalling of concrete all together are extensive damage, while the failure of the column means that a shear occurred at the base [4]. [PERSON] et al. [18] tested RC and Concrete-Filled Fiber-Reinforced Polymer (FRP) tube (CFFT) bridge columns at a scale of 1:5. CFFT columns are reinforced only with longitudinal reinforcement, while RC columns have spiral hoops in addition to longitudinal reinforcement, shown in Figure 5. The quantity and distance of the explosives were not provided for safety reasons. The columns experienced minimal visual damage, but measurements showed that both concrete and steel experienced large loads and strains. In the residual test, CFFT columns showed greater strength and ductility than RC columns. Figure 4: Test setup [4; 8]. Figure 3: Test setup in [7] and [9]. [PERSON] et al. [5] made the same prototype of the bridge columns as [9] and exposed them to the same blast load scenario. To improve the behavior of the steel jacked columns to the explosion, they added structural steel collars at the top and bottom of the column. The steel collar at the base of the steel jacked RC column is shown in Figure 2 in [5]. They concluded that the modified column was effective in preventing direct shear and had increased ductility. The obtained maximum base rotation ranges from 8.6 to 10.3\({}^{\circ}\), and all the columns showed satisfactory behavior. [PERSON] et al. [23] experimentally tested two RC bridge columns in scale 1:3 under 1 kg TNT contact explosion placed at the height of 33 cm from the ground. As a retaining structure that prevents the rotation and displacement of the column at the top, they used a wall with the opening that was placed at a distance of 1.4 m from the detonation point. Both columns experienced spallation and crushing of concrete cover, but the stirrup fracture was observed only in the square column. The damages to the front and back sides of the circular and square columns are shown in Figure 13. Therefore, the test results showed that the square column had more severe damage than the circular column. [PERSON] et al. [29] investigated the impact of contact explosions of 1 kg, 2 kg, and 3 kg of TNT on the mode of failure and original and residual axial capacity of Ultra-High Performance Cementitious Composite Filled Steel Tube (UHPTCC-FST) bridge column. The columns were made in 1:4 scale and are tested horizontally, and the views of the test setup are shown in Figure 6. The top of the column is pinned, and the bottom of the column is fixed.