# Black Loaded Columns--State of the Art Review
## 3 Numerical Modeling
Conventional Weapon Effects Predictions (ConWep) [80] and BlastX [81] are programs used to calculate the effect of a blast wave from different types of detonation. ConWep is more used for air-blast calculations, including free-field and reflected blast pressure histories from the free-air, surface, and hemispherical burst explosions, and BlastX calculates internal blast pressure histories. BlastX is based on semi-empirical methods, including nonlinear addition laws for blast pressures from multiple reflecting surfaces based on computational fluid dynamics. Second-order Hydrodynamic Automatic Mesh Refinement Code (SHAMRC) [82] is also used to investigate high explosive and blast effects based on finite-difference computational fluid dynamics (CFD) code. Nonlin [83] does not make the empirical adjustments just for blast loads because it is initially designed for earthquake loads. It has similarities with SPAn32 [84] because it performs a nonlinear dynamic response history analysis taking bilinear material properties. Both programs are based on the analysis of a system with a single degree of freedom (SDOF). MSC.Dytran [85] is an explicit finite element analysis (FEA) solution for simulating blast load effects and analyzing the complex nonlinear behavior that structures undergo during detonation. Ansys Autodyn [86], LS-Dyna [87], and Abaqus [88] are programs that provide the ability to simulate detonation, wave propagation from an explosion, interaction with a structure, and nonlinear material behavior, which are known as hydrocode programs specialized for simulations in fluid dynamics. [PERSON] et al. [46], in their research, compared three methods with three different resolutions for air blast prediction. In the scenario of below-deck detonation, ConWep has a low resolution of air blast prediction, and the charge can be observed as hemispherical or spherical, while BlastX has a medium resolution and considers the shape of the charge and reflections of the blast pressure. The 3D bridge and blast load can be modeled in the SHAMRC because it is an advanced Eulerian-based finite difference code that has high resolution. Research shows that the highest resolution is not always necessary, as it is a mostly low resolution that provides a conservative design. The authors stated that additional analysis is needed to determine the most economical and sufficiently precise tool for a particular problem [46]. The shape of the explosive also drastically affects the resulting pressure and impulse, so it is necessary to use a program that allows the input of charge geometry. [PERSON] et al. [36] determined concrete breaching using ConWep and calculated flexural response and support rotation on a reduced diameter column in SPAn32. They concluded that the strength of concrete does not significantly affect the maximum rotation of the support, but it does affect breaching, i.e., the lower strength causes greater breaching. [PERSON] et al. [2] use SPAn32 to calculate the flexural response of the columns and to define the equivalent SDOF stiffness and mass parameters based on the column properties. For the calculation of the blast load pressure history, the BlastX program was used. Other useful programs are AT Blast [89] and Nonlin. For the calculation of the pressure-impulse history using AT Blast, it is necessary to know the charge weight, angle of incidence, and standoff distance. However, AT Blast does not consider the effects of multiple reflections under the bridge explosions. They list four categories of bridge design concerning their importance, where category 1 represents very important bridges, and category 4, unimportant. [PERSON] et al. did not take the real conditions of the ground and energy absorption by creating craters but the ideal reflecting surface. Footing instability, however, could also result from large ground deformations, and this aspect of behavior must also be addressed. [PERSON] et al. [48] numerically simulated RC and composite columns in LS-Dyna for the contact-placed TNT charges from 2.5 to 25 kg.