# Black Loaded Columns--State of the Art Review
## 4 Discussion and Conclusions
### Numerical Modeling  
Numerical simulations make it possible to study the effect of large amounts of explosions (more than 1000 kg) on columns in full-scale. The most widely used software for analyzing the nonlinear behavior of elements on blast load is LS-Dyna. The most accurate simulation of the blast pressure requires as finer mesh as possible, which leads to a long duration of simulations and congestion of the computer processor. Due to the use of a larger mesh size than recommended, the LS-Dyna underestimates the pressures. Most researchers use the ConWep program to calculate pressures and import the resulting pressures into LS-Dyna.  
Defining a model of concrete material is the most demanding because many parameters affect its behavior. Karagozian and Case (KC) concrete is mostly used in LS-Dyna. The proper definition of erosion criteria has proven to be very important in modeling column damage.  
The position of the explosive plays a significant role in the behavior of the column. Placing the charge in the far-field causes a uniformly distributed load per column and global response, while a charge placed in the near-field, close-in, and contact creates local damage.  
Moreover, the columns exposed to the charge placed in the lower half showed greater damage and lowered residual capacity than the columns where the charge was placed in the middle.  
In all fields (far, near, close-in), changes in the quantity, shape, and position of the explosives showed a great impact on column behavior. The shape of the column, the ratio of reinforcement, and the concrete grade showed an influence only at small-scaled distances. The concrete grade does not affect the rotation of the column but does affect the reduction in concrete breach and spallation.  
Until recently, the axial load on bridge columns was neglected in the calculation because it was considered to be on the safe side. However, numerical simulations showed that axial load has a large impact on increasing damage when the charge is placed near the column or in contact with the column and should not be neglected.  
Conceptualization, S.L. and H.D.; methodology, S.L. and H.D.; resources, S.L. and H.D.; data curation, S.L.; writing--original draft preparation, S.L.; writing--review and editing, H.D.; visualization, S.L.; supervision, H.D.; project administration, H.D.; funding acquisition, H.D. All authors have read and agreed to the published version of the manuscript.  
This research was in part funded by Croatian Science Foundation (HRZZ), grant number UIP-2017-05-7041.  
Not applicable.  
Data Availability Statement: Data available on request due to restrictions, e.g., privacy or ethics. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to limited access to certain literature used in the article.  
This paper has been supported in part by Croatian Science Foundation (HRZZ) under the project UIP-2017-05-7041 \"Blast Load Capacity of Highway Bridge Columns\", and support for this research is gratefully acknowledged.  
The authors declare no conflict of interest.