# Black Loaded Columns--State of the Art Review
## 2 Experimental Testing
### Bridge Columns  
The experiments were carried out on standard RC columns, additionally retrofitted columns, and improved composite concrete columns. The columns are exposed to various scenarios of explosive attacks. In addition to the type of column, the scenarios also differ in the position, type, and amount of explosives. [PERSON] et al. (2019) provided the list of possible terrorist courses of action and indicated that the hand placed explosives on the column and large truck-bomb below the bridge superstructure can destroy columns and cause bridge collapse. Due to similarities between the effects of the explosions and earthquakes, [PERSON] et al. (2016) developed a multi-hazard pier concept that they expect to provide a satisfying level of protection against failure under both loadings. All specimens were concrete-filled circular steel columns (CFCSC) with three different diameters (10.16 cm (4\"), 12.7 cm (5\"), 15.24 cm (6\")) and a minimum steel thickness of 3.2 mm. Specimens were made in 1:4 scale of the prototype bridge columns. Due to security reasons, the actual values of charge weights and standoff distances are not provided. Experimental results showed that even a minimal increase in standoff distance and column diameter significantly reduces column deformation. The CFCS columns showed ductile behavior and high resistance to the effects of the explosion (2016). The same scale and scenario when the explosive was located under the bridge in a car placed near to the column were examined in (2016). They assumed the charge weight similar to the blast weights predicted in FEMA (2003) (2016) and FHWA (2003) (2016). Charges are set at heights of 0.25 m and 0.75 m, which correspond to the actual height of 1 m (car bomb) and the half column height, respectively. They concluded that only steel jacketing is not enough to provide adequate resistance to the large shear forces influencing the bottom of the column. Therefore, they found that a better solution is using a fully concrete-filled steel tube (CFST) continuously embedded into the footing. CFST columns provided ductile behavior and sufficient resistance to the lateral forces from earthquakes and explosions. Moreover, the advantage of CFST columns is that they do not have a breach and a spall of concrete, i.e., they do not produce flying debris (2016). Figure 2 shows the connection concept between the foundation beam and the CFST column, which provides the full moment capacity of the column. At a rotation of 3.8\({}^{\circ}\) of the bottom of the column, plastic deformation is visible but without cracking of the concrete. The first cracks occur at a rotation of 8.3\({}^{\circ}\), while the fracture of the steel tube occurs at 17\({}^{\circ}\). At the height of the explosive charge, pits and notches appeared on the steel tube, while concrete cracks occurred on the tension side at the bottom and top of the column due to the rigid boundary conditions (2016). They assumed the same blast scenario as [PERSON] et al. (2016) in their work at the same scale of 1:4, but there were four columns in the test specimen while the bridge prototype has three. Figure 3 shows the test setup for the same blast load scenario but on different types of columns. The RC column exhibited shear failure at the base and cracking of concrete along the column (2016), RC SJ shear failure (2016), and CFST column flexural failure