# Numerical investigation of a new structural configuration of a concrete barrier wall under the effect of blast loads

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## Abstract

In this study, a non-linear three-dimensional hydrocode numerical simulation was carried out using AUTODYN-3D, which is an extensive code dealing with explosion problems. A high explosive material (comp-B) is blasted against several concrete wall barriers. The model was first validated using referenced experimental tests and has shown good results. Several numerical models were carried out to study the effect of changing the shape of wall barrier from flat to convex curve and concave curve, and also investigated the effect of changing the angle of curvature. The results showed that changing the shape of a wall barrier from flat to convex curve has the best performance in mitigating the effect of blast waves. It is also concluded that convex walls with 60° angle of curvature have the best performance compared to other barrier walls.

## Keywords

Concrete Explosion Composition B Wall barrier Numerical simulation Blast wave## Introduction

With the increasing threat of terrorism and the rapid development of technology, the probability of accidental explosions such as incident blasts, mine explosions, and terrorist attacks has increased; protecting important structures against explosive impacts has become a great concern (Goel and Matsagar 2013; Hetherington and Smith 2014; Hinman and Engineers 2011; Li et al. 2009; Remennikov and Rose 2007; Wang et al. 2013; Wu 2012; Wu et al. 2010; Zhou and Hao 2008).

The intensive pressure of these explosions causes critical damage to the nearby buildings and human beings in the perimeter of the explosion (Alsubaei 2015; Baker et al. 2012; Berger et al. 2015). To reduce the losses of lives and building resources, protecting structures against blast load is studied extensively with different techniques or methods. One of these techniques is using different sizes and shapes of Barriers to diffract the blast wave, leaving behind it a complex flow field that changes the load exerted on the target (Aghdamy et al. 2013; Luccioni and Ambrosini 2010; Tiwari et al. 2016; Xia et al. 2014).

Numerous researchers have studied the effects of shock waves on different geometric configurations theoretically, numerically, and experimentally (Azmi et al. 2019; Chaudhuri et al. 2013; Igra et al. 2001; Lu et al. 2005; Nam et al. 2016; Nurick et al. 1996, 2006; Smith et al. 1999). Such as, Rouse (2010) studied the mitigating effects of a blast barrier wall. This study used a scaling method to make an experimental research on the effect of the barrier wall in reducing the effect of the pressure wave on the area behind the barrier. Two parameters were studied in this research: the barrier height and the standoff distance where the study used 73 grams of hemi-spherical-shaped C4 explosive charges on a barrier wall.

Berger et al. (2015) investigated experimentally and numerically using different barrier configurations to attenuate the shock wave effects. The experiments were performed in a shock tube equipped with a high-speed camera. Aghdamy et al. (2013) investigated numerically the effect of retrofitting masonry walls subjected to blast with nano-particle reinforced polymer and aluminum foam numerical models were validated using available test data. Different pressures and impulses were applied on the retrofitted walls and their efficiency was investigated. Xia et al. (2014) performed a numerical investigation on reinforced concrete cladded with metallic foam using LS-dyna. The model was validated using field blast testing.

Parametric studies were conducted to investigate the effect of the thickness of the reinforced concrete members and the different properties of foam. Due to the development in the engineering technologies, researchers/designers developed a new way of thinking to solve the daily life problems. Recently, numerous researchers have concluded that the inspiration from nature (Biomimicry) is the optimum solution to solve the most sophisticated engineering problems (Rong and Thong 2015).

Bio-inspired technique is an approach to solve the human challenges through studying the natures’ designs and then imitate/mimic them to seek sustainable solutions (Wilson 2008). Since, the current work discusses the protection/armor systems, several investigations have been carried out to study the armor mechanisms, protection systems, ballistics armor, and flexible armor; for instance, the multifunctional shell of chitons. The shell consists of two completely different segmented armors, central plates, and peripheral scales, which are seamlessly integrated together in one system. The plates and scales differ in size, degrees of freedom, and level of protection (Connors 2014). Another example is that the seahorse tail is composed of subdermal bony plates arranged in articulating ring-like segments that overlap for controlled ventral bending and twisting (Porter et al. 2013). The bony plates are highly deformable materials designed to slide past one another and buckle when compressed. This complex plate and segment motion, along with the unique hardness distribution and structural hierarchy of each plate, provide seahorses with joint flexibility while shielding them against impact and crushing.

Based on the aforementioned literature review, it is concluded that there are different techniques that can be used to mitigate the effect of shock waves. The shape configuration of the concrete barrier wall is modified from the ordinary flat barrier wall to curved barrier wall mimicking the protecting shield of the turtle and armadillo where their curved shield protects them from the various attacks of enemies and it provides these animals with the maximum protection it can offer according to its characteristics. Their shield could have a lot of shapes to protect them but nature gave them the curved shape, so we thought that this shape is the best protection for them, so we could benefit from this shape in protection from various loads (in our case blast loads).

Therefore, the new proposed protected wall is based on these natural facts. Numerical analysis is performed to simulate the effect of the explosion on the new proposed and traditional configuration of a concrete barrier wall using finite-element software AUTODYN-3D (Autodyn 2005). The finite-element model is validated by available published experimental tests (Hajek et al. 2016). Then, the effect of the geometrical shape of a wall barrier is studied as a comparison is made between flat and curved wall with different angles of curvature to achieve the best performance in the mitigation of the blast wave resulting from the detonation.

## Numerical simulations

Numerical simulations are an important means of studying the effect of explosion and blast effects on different structures as conducting experimental investigations is very expensive and needs a lot of equipment and precautions during execution.

### Numerical tool: hydrocode

A computer program that is capable of computing strains, stresses, velocities, and propagation of shock waves as a function of time and position is known as a hydrocode. In this study, the hydrocode simulations on the explosion effect on a concrete target are performed using AUTODYN-3D (Mizukaki 2007). In AUTODYN-3D, the fundamental equations together with the initial and boundary conditions are solved using a finite-difference scheme.

### Model validation

This paper presents a 3D hydrocode simulation using AUTODYN-3D (Autodyn 2005) on the effect of explosion on a barrier wall target. The experimental data published by Hajek et al. (2016) for two tests carried out using a 500 g explosive are used for validation.

### Proposed structural configuration

The curved barrier wall is placed in two positions, the first one the side facing the blast wave is the convex side, while the second one the side facing the blast wave is the concave side with different angles of curvature Ø (50°, 60°, and 70°) which are subjected to the detonation of a 10 kg comp-B detonated at a distance 2 m from the barrier wall (Yusof et al. 2014) to detect the geometrical shape which gives the best performance in the mitigation of the blast wave resulting from the detonation.

### Finite-element model

Remap technique was used during numerical simulation (Autodyn 2005). The initial detonation and blast wave propagation of the explosive in free air are first calculated in a 2D domain; the result was then remapped into a 3D space. This technique is used to save time and make the model more efficient.

The concrete target is described with the Lagrange solver. Composition B is modeled using Jones–Wilkins–Lee equation of state which models the pressure generated by chemical energy in an explosion. Air was modeled by an ideal gas equation of state, which is one of the simplest forms of equation of state.

### Numerical results and analysis

Peak pressure for gauges

Model | TFBW | CCVW-70 | CCVW-60 | CCVW-50 | CCXW-70 | CCXW-60 | CCXW-50 |
---|---|---|---|---|---|---|---|

Gauge no. | Peak pressure (kPa) | ||||||

1 | 233 | 1334 | 232 | 365 | 799 | 110 | 446 |

2 | 2203 | 2151 | 1676 | 1332 | 2169 | 428 | 1410 |

3 | 233 | 1139 | 356 | 223 | 1098 | 460 | 104 |

4 | 870 | 698 | 306 | 293 | 389 | 142 | 379 |

5 | 1497 | 3355 | 1335 | 1591 | 1666 | 1038 | 1401 |

6 | 870 | 202 | 378 | 550 | 304 | 146 | 578 |

7 | 282 | 308 | 162 | 234 | 308 | 124 | 237 |

#### Over-pressure

Gauge 2 is in the front middle part of the concrete barrier. As shown in Fig. 14, the results of pressure measured on this gauge show different responses of different barrier shapes and configurations on the pressure measured in this location as the pressure measured in the model TFBW is the highest and it decreases slightly in model CCVW70 (2151 kPa). When the angle of curvature (Ø) of the wall decreased to 60° (model CCVW60), the pressure decreased to 1676 kPa, and then, the pressure decreased much more to 1332 kPa when the angle of curvature (Ø) decreased to 50° (CCVW50).

For gauge 2 as shown in Fig. 15, the pressure measured for the model CCXW-70 is 2169 kPa. When the angle of curvature (Ø) of the wall decreased to 60° (model CCXW-60), the pressure decreased to 428 kPa, and then, the pressure increased again to 1410 kPa when the angle of curvature (Ø) decreased to 50° (CCXW-50).

Gauge 4 is in the lower back part of the concrete barrier in the back face. As shown in Fig. 16, the results of pressure measured on this gauge show different responses of different barrier shapes and configurations on the pressure measured in this location as the pressure measured in the model TFBW is higher (870 kPa) than the pressure measured in the model CCVW-70 (698 kPa), and when the angle of curvature (Ø) decreased to 60° in model CCVW-60, the pressure decreased to 306 kPa, and then, it decreased more to 293 kPa when the angle of curvature (Ø) decreased to 50° in model CCVW-50.

However, for gauge 4, as shown in Fig. 17, the pressure measured in the model CCXW-70 is 389 kPa, and when the angle of curvature (Ø) decreased to 60° in model CCXW-60, the pressure decreased to 142 kPa, and then, it increased again to 379 kPa when the angle of curvature (Ø) decreased to 50° in model CCXW-50.

Gauge 6 is in the upper back part of the concrete barrier in the back face. As shown in Fig. 18, the results of pressure measured on this gauge show different responses of different barrier shapes and configurations on the pressure measured in this location as the pressure measured on the flat wall in the model TFBW is 870 which is higher than the pressure measured in the model CCVW-70 (202 kPa).

However, when the angle of curvature (Ø) decreased to 60° in the model CCVW-60, the pressure increased to 378 kPa, and then, it increased once again to 550 kPa when the angle of curvature (Ø) decreased to 50° in the model CCVW-50.

While for gauge 6, as shown in Fig. 19, pressure measured in the model CCXW-70 is 304 kPa, but when the angle of curvature (Ø) decreased to 60° in the model CCXW-60, the pressure increased to 460 kPa, and then it increased once again to 578 kPa when the angle of curvature (Ø) decreased to 50° in the model CCXW-50.

#### Internal energy

^{7}μj), while the concrete barrier wall CCXW-60 has the highest internal energy (1.486e

^{8}μj).

### Discussion

When comparing the results of the concave and the convex wall, we can conclude that for the near side facing the detonation wave, the pressure values have no great difference for the middle portion, while for the upper and lower portion, the values are remarkably lower for the convex wall than the concave wall, the cause of this is the reflected waves as when the incident wave impacts the convex wall, it diffracts away from the wall in the upper and lower direction, while for the concave wall, it reflects them in the direction of the upper and lower portion which causes the pressure to go high.

For the internal energy, when we analyze the results, it is obvious that when the internal energy of the barrier wall decreases, this shows that the barrier wall has low resistance against blast loads, and hence, the pressure behind the barrier wall increases. On the contrary, when the internal energy of the barrier wall increases, this shows that the barrier wall has high resistance against blast loads; hence, the pressure behind the barrier wall decreases.

## Conclusion

- 1.
The numerical model presented has a good agreement with the experimental work in the validation; hence, it can be used for parametric studies.

- 2.
After comparing the different structural configurations proposed in our study, the best configuration for mitigation of blast hazards is using convex barrier walls facing the pressure wave as shown by model CCXW-60 which gave the best performance for the protection of the area behind the wall barrier where the pressure for gauge 7 behind the barrier wall for the model CCXW-60 was lower by 23.4% than the pressure measured for the concave wall (CCVW-60) with the same angle of curvature and was lower by 56% than the pressure measured for the flat wall (TFBW).

- 3.
The convex barrier walls have the best performance in lowering the pressure affecting the wall which will consequently affect the fragments ejecting from the wall as the pressure measured on the front face in the convex walls is lower than the concave walls with an average percentage of 63.2% and lower than the flat wall with an average percentage of 66.25%. While for the back face, the pressure measured of the convex walls is lower than the concave walls with an average percentage of 45.7% and lower than the flat wall with an average percentage of 65.85%.

- 4.
Moreover, it is also concluded that varying the angle of curvature has a notable influence on the effect of explosion on the wall barrier and the area protected by the barrier where the pressure measured behind the convex wall with 60° angle of curvature is lower by 59.7% than the pressure measured behind the convex wall with 70° angle of curvature and is lower by 47.68% than the pressure measured behind the convex wall with 50° angle of curvature. The current work proves that the response of the curvature configuration concept is much better than the flat configuration under the effect of the blast waves.

- 5.
The internal energy of barrier walls were measured and showed that the barrier wall with the highest internal energy has the most resistance to blast loads and vice versa.

## Notes

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