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Authors:Adam A Dennis, Sam E Rigby Abstract: International Journal of Protective Structures, Ahead of Print. Machine learning (ML) methods are becoming more prominent in blast engineering applications, with their adaptability to new scenarios and rapid computation times providing key benefits when compared to empirical methods and physics-based approaches, respectively. However, ML approaches commonly used for blast analyses are regularly provided with inputs relating to domain-specific parameters, restricting their use beyond the initial problem set and reducing their generality. This article presents the ‘Direction-encoded Neural Network’ (DeNN); a novel way to structure an Artificial Neural Network (ANN) to predict blast loading in obstructed environments. Each point of interest (POI) is represented by the proximity to its surroundings and the shortest travel path of the blast wave in order to prime the network to learn the underlying physics of the problem. Furthermore, a bespoke wave reflection equation creates a zone of influence around each point so that obstacles are only captured in the network’s inputs if they would alter the path of the wave. It is shown that the DeNN can predict peak overpressures with mean absolute errors ∼5 kPa for unseen, complex domains of any shape or size, when compared to the results from physics-based numerical models with ∼30 times the solution time of the DeNN. The network is used to develop maps of likely human injury following detonation of a high explosive in an internal environment, with eardrum rupture levels being correctly predicted for over 93% of unseen test points. It is therefore highly suited for use in probabilistic, risk-based analyses which are currently impractical due to excessive computational cost. Citation: International Journal of Protective Structures PubDate: 2023-06-01T11:38:52Z DOI: 10.1177/20414196231177364
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Authors:Hugo Bento Rebelo, Beatriz Assunção, Chiara Bedon, Filipe Amarante dos Santos Abstract: International Journal of Protective Structures, Ahead of Print. This paper is focused on the study of innovative bi-stable supports to improve the impact performance of point-fixed glass panels, for typical use in facades. To mitigate the effects of impact and reduce potential risk for people, the introduction of innovative, bi-stable, mitigation devices between the fixing system and the primary building structure is addressed. The proposed dissipative system is able to control and minimise the input force which is transmitted to the primary building, controlling the damage around the supports and preventing the detachment of the glass panels. Based on LS-Dyna Finite-Element (FE) models, the proposed protection system is designed to have a snap-through behaviour under impact. The performance of the system is quantified for two different glazing systems, which are numerically investigated under various impact configurations. Citation: International Journal of Protective Structures PubDate: 2023-06-01T11:24:45Z DOI: 10.1177/20414196231175979
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Authors:J Liu, CZ Gao, ZY Sun, JW Yin Abstract: International Journal of Protective Structures, Ahead of Print. In the near field, the air blast peak overpressure from cylindrical charges may vary by several times with angles at the same scaled distance. We propose an estimation equation for the peak overpressure from cylindrical charges, which can predict the peak overpressure from cylindrical charges at any positions in the near field. The estimation equation is in the form of piecewise function which contains three variables of length-to-diameter ratio, angle and scaled distance, and the applicability of our estimation equation is verified by experiment and simulation. After preliminary verification, the application range of length-to-diameter ratio of cylindrical charge is [math] and that of scaled distance is [math]. The estimation equation can be rapidly applied to the assessment of near-field target damage and protection against air blast from cylindrical charges, which is a significant supplement to the traditional empirical equations for spherical charge. Citation: International Journal of Protective Structures PubDate: 2023-05-19T09:48:56Z DOI: 10.1177/20414196231177358
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Authors:Kirtika Samanta, Priti Maheshwari Abstract: International Journal of Protective Structures, Ahead of Print. Behaviour of machine foundations is investigated in this study under harmonic loading with varying frequency and pulse loading. Owing to excessive vibrations from the pulse, the machine encounters an emergency shutdown where the machine’s exciting frequency reduces to zero exponentially. The analysis is performed considering an elastic plastic single degree of freedom system with hardening and softening behaviour. Two cases are analysed depending on the time of application of pulse loading to the foundation system. For both the cases, the governing equations of motion are acquired and solved numerically using the fourth order Runge-Kutta method. Using these solutions, displacement-time graphs are obtained for a variety of parameters such as time constant, hardening/softening index, mass of machine and the foundation block, stiffness, pulse load magnitude, damping ratio and decay coefficient to study their influence on the behaviour of the machine-foundation system. The study helps in predicting the dynamic response of foundations under the emergency shutdown conditions due to pulse loading. Further, these also help in taking the decision if there exists a need for vibration barriers to have the displacements well within the permissible limits. Citation: International Journal of Protective Structures PubDate: 2023-05-11T11:14:50Z DOI: 10.1177/20414196231174916
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Authors:Ayham Ali Salamy, Ibrahim Hammoud Abstract: International Journal of Protective Structures, Ahead of Print. The field tests conducted by the American Engineering Research Associates (ERA) provided important results about the distribution and extension of the damage zones and the failure area that occurred in unlined tunnels as a result of buried explosions in the rock mass surrounding these tunnels. Despite the importance of these results, they did not include specific values for the failure thickness and the fracture angle in the damaged tunnel sections. In the current study, a 3D numerical model is used to simulate one of ERA’s tests using ABAQUS. In this model, the impact of a buried explosion on a tunnel located at (5m) away from the center of the detonation is studied. The results of this model are in good agreement with the published results of ERA’s tests. In addition, the current numerical results give complete values for the change in the failure thickness and the fracture angle over the entire length of the damaged zones of the tunnel. The results of the current study show that the thickness of the failure remains almost constant beyond damage zone 1, while the angle of the fracture decreases remarkably as the charge-to-tunnel distance increases, which causes a decrease in the failure area. Citation: International Journal of Protective Structures PubDate: 2023-04-04T11:25:09Z DOI: 10.1177/20414196231167596
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Authors:Cheng-Wei Hung, Ying-Kuan Tsai, Li-Kai Chien, Sheng-Jung Pi Abstract: International Journal of Protective Structures, Ahead of Print. This study adopted the LS-DYNA mapping algorithm to implement a numerical simulation of a near-surface burst and steel plate non-contact explosion experiments. The rationality and reliability of the mapping technique used in the numerical simulation were validated by a comparison between the experiments and the numerical simulation. The findings showed that the numerical simulation result was consistent with the experimental blast attenuation, meaning the numerical mapping technique could effectively enhance the simulation accuracy and could reflect the experimental blast wave propagation. Citation: International Journal of Protective Structures PubDate: 2023-03-29T01:16:16Z DOI: 10.1177/20414196231166067
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Authors:Andria Antoniou, Tore Børvik, Martin Kristoffersen Abstract: International Journal of Protective Structures, Ahead of Print. Concrete is used for protective structures all over the world. Accurate response estimates to a given threat is vital for designing such structures. Concrete models often require numerous input parameters for which sufficient experimental data can be challenging to obtain. Some models are accompanied by parameter generators which use the unconfined compression strength to extrapolate the remainder of the parameters based on experimental databases. This study investigates simulation of ballistic impact on high-strength concrete with 75 MPa nominal unconfined cylindrical compressive strength. The first objective is to investigate the accuracy parameter generators to produce input data for commonly used concrete material models. The second objective is to establish and evaluate a simplified parameter calibration procedure based on standard material experiments and data from the literature. The results employing parameter generators varied notably between the models while still giving decent ballpark estimates. The parameters obtained from inverse modelling of standardized material tests improved the results significantly. The findings of this study recommend caution when using automatic parameter generators. Although a detailed calibration of these concrete models is complicated, a simplified calibration gives reasonable predictions, making this the advisable approach for designing concrete protective structures. Citation: International Journal of Protective Structures PubDate: 2023-03-24T01:10:21Z DOI: 10.1177/20414196231164431
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Authors:Vladimir R. Feldgun, David Z. Yankelevsky, Yuri S. Karinski Abstract: International Journal of Protective Structures, Ahead of Print. This paper presents theoretical research that is supported by experimental data, aiming at investigating and explaining unexpected experimental results that were obtained on low velocity pounding response of adjacent concrete rods. The experimental results indicate inelastic response expressed by the post-impact relative velocity and coefficient of restitution that is smaller than one, although elastic response is expected. This research conjectures that the inspected response is due to the roughness of the impacting surfaces. A theoretical analytical and a following numerical investigation examined the behavior of the surface roughness represented by small size asperities in an idealized model. Analysis of the asperity behavior clarified its inelastic behavior that affects major parameters on the response. An integrated parameter has been identified, which includes major parameters of the asperity affecting the dynamic behavior and helping to relate the geometrical parameters of an asperity with the measured pounding data. It was found that asperities may explain the energy absorption during low velocity pounding. This explains the lower coefficient of restitution than expected even at low velocity pounding. An effective and simple analytical approach is developed to simulate the rods collision with an idealized surface asperity and demonstrates the role of the asperities on a realistic simulation of the experimental result. Citation: International Journal of Protective Structures PubDate: 2023-03-23T12:47:13Z DOI: 10.1177/20414196231166017
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Authors:S. M. Anas, Mohd Shariq, Mehtab Alam, Mohammad Umair Abstract: International Journal of Protective Structures, Ahead of Print. Explosions are continually occurring in many parts of the world endangering human lives and seriously affecting the health of infrastructures and facilities. Low-rise buildings having a height of fewer than 13 m are load-bearing structures generally made of unreinforced masonry (URM), particularly in semi-urban areas, villages, and war-prone border areas. Many structures of importance including buildings constructed in the pre- and post-independence era of courts, monuments, etc., are masonry load-bearing structures. URM is also used as non–load-bearing partition walls and compound/boundary walls. Such walls are susceptible to out-of-plane blast loading. Under such loadings, these walls fail to survive and thus either get severely damaged or collapsed, jeopardizing the stability of the entire structure. Resistance of masonry walls against blast loading is vital for the safety of the building and its users as injuries sustained and casualties are generally not caused due to explosion, but by the brittle dynamic fracture and fragments of masonry walls, window glass panes shattering, and other secondary objects propelled as missiles by the blasts. In general, buildings are not designed for blast loading. For the safety of the building users, it is imperative that the walls must withstand such short-duration high-magnitude extreme loadings without not only undergoing catastrophic collapse but also not producing deadly fragments which could cause grievous injuries to the users. To protect URM walls from high-intensity blast waves, an out-of-box wall protecting technique using foams of polymer (e.g., polyurethane) and metals namely; aluminum and titanium, is considered on the face of the wall exposed to the blast pressure. This study describes a numerical technique implemented in ABAQUS/Explicit software to predict the overall anti-blast performance of URM wall strengthened externally with the above three different crashworthy foams. For this purpose, a braced URM wall made of clay bricks, with two transverse bracing walls one at each end on the same side, tested experimentally by Badshah et al. in the year 2021 under the chemical explosive loads of 4.34 kg and 7.39 kg-TNT, respectively, at scaled distances 2.19 m/kg1/3 and 1.83 m/kg1/3 is considered as the reference model and is validated against the test observations. Explosion load is modeled with ABAQUS built-in ConWep simulation program to simulate the wall-explosion wave interactions in the free field. Material nonlinearities of the brickwork have been attributed to bricks, joint-mortar, and brick-mortar interfaces through constitutive laws considering strain-rate effects. The foams are modeled using ABAQUS’s inbuilt Crushable Foam Plasticity Hardening model considering foam hardening and rate-dependent schemes. Results show that the higher Young’s modulus and inelastic stiffness of the foams contribute to dissipating more explosion energy and improve the resistance of the walls from savage explosions. Citation: International Journal of Protective Structures PubDate: 2023-03-17T12:53:21Z DOI: 10.1177/20414196231164432
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Authors:Richard A Perkins, Chris Duncan, Daniel Johnson, Tonya Stone, Jesse Sherburn, Mei Chandler, Robert Moser, Bhasker Paliwal, Raj K Prabhu, Youssef Hammi Abstract: International Journal of Protective Structures, Ahead of Print. Concrete offers superior strength in compressive loadings and is implemented for many applications. The high compressive strengths enable concrete to resist high strain rate loading scenarios such as ballistic impacts. A variety of concrete denoted as Cor-Tuf, which is classified as ultra-high-performance concrete with a compressive strength of 210 MPa, is evaluated in this study. The response of this concrete is assessed through a finite element analysis under the high strain rate loadings of ballistic impacts. To capture the response of the concrete, a plasticity and damage constitutive model denoted as the HJC model is implemented. The parameters of this model are calibrated to the Cor-Tuf concrete using confined compression experiments, unconfined compression experiments, and shock experiments. The concrete target is impacted at speeds between 610 m/s through 1112 m/s, and the results are compared to existing experimental data. Our results show that the HJC model can predict the response of this impact to the Cor-Tuf concrete targets as an average error of 5.85% is found. The results of this study present parameters which can be implemented with the HJC concrete model for future studies to model the response of the Cor-Tuf UHPC. Citation: International Journal of Protective Structures PubDate: 2023-02-28T09:30:43Z DOI: 10.1177/20414196231160235
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Authors:Mohammad Mohsin Khan, Mohd Ashraf Iqbal Abstract: International Journal of Protective Structures, Ahead of Print. Split Hopkinson pressure bar (SHPB) system is significantly used for dynamic material characterization in the range of strain rates 102–104 s-1; however, there is no standard design methodology or readily available technique for the development of this apparatus. The objective of this study is to present a detailed design, development and calibration of SHPB apparatus for dynamic material characterization of concrete in compression. The calibration of the loading and bar components has been presented with the help of experimental results and validated following an analytical approach for one-dimensional stress wave propagation. The experimental pulse duration, 124.5 microsecond, and elastic wave speed, 4820 m/s, was measured with 2% deviation from the analytical results. Under three different impact velocities, a minimum 1.09% and maximum 4.14% decrement was observed in the incident wave as compared to analytical formulation. The recorded strain signals were captured in the transmission bar with a decrement of 1, 3, and 3.3% in peak strain when compared to the incident bar, at 4.5, 4.9, and 5.7 m/s impact velocities. The incident and transmission bars had almost identical wave characteristics demonstrating that the bar system has been perfectly and precisely aligned, and almost complete wave transfer is seen to have occurred. Experiments performed on M35 concrete specimens using the developed SHPB setup have been presented and discussed. The results demonstrated that the developed SHPB setup is capable to provide accurate results for the dynamic material characterization of concrete at high strain rate loading. Citation: International Journal of Protective Structures PubDate: 2023-02-08T09:34:19Z DOI: 10.1177/20414196231155947
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Authors:Bowen Zhao, Nan Jiang, Chuanbo Zhou, Yingkang Yao, Wenbin Zhou, Zhongwei Cai Abstract: International Journal of Protective Structures, Ahead of Print. Modern railroad infrastructure is subject to blast vibrations. The dynamic safety of an operating railroad under the influence of tunnel blasting is a primary problem for metro development in urban areas. In this paper, the blasting excavation of Wuhan Metro Line 5 was selected as a case. The ballast rail- sleeper- ballast bed composite structure numerical model was developed and validated in order to evaluate the ballast railway’s safety. The smoothed particle hydrodynamics element was chosen to replicate the ballast bed due to the instability and unpredictability of the ballast bed constructed from crushed stone. Further analysis was conducted on the dynamic response characteristics of the ballast rail-sleeper-ballast bed composite structure. On the basis of the parameter calculation and analysis, a prediction model of the blast vibration velocity of the ballast rail under blasting conditions was developed. Next, the rail was simulated as a semi-infinite Euler beam and placed on the Kelvin foundation to calculate the rail displacement at the train’s limited operation speed. By substituting the maximum rail displacement when the train is running at maximum speed into the rail velocity prediction model, it is possible to determine the maximum blast velocity that the rail can withstand in this instance. In this case, the ballast bed, sleeper, and ballast rail were also deemed safe. Citation: International Journal of Protective Structures PubDate: 2023-01-09T05:35:04Z DOI: 10.1177/20414196221150661
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Authors:Dain G. Farrimond, Scott Woolford, Andrew Tyas, Sam E. Rigby, Samuel D. Clarke, Andrew Barr, Mark Whittaker, Dan J. Pope Abstract: International Journal of Protective Structures, Ahead of Print. A significant amount of scientific effort has been dedicated to measuring and understanding the effects of explosions, leading to the development of semi-empirical methods for rapid prediction of blast load parameters. The most well-known of these, termed the Kingery and Bulmash method, makes use of polylogarithmic curves derived from a compilation of medium to large scale experimental tests performed over many decades. However, there is still no general consensus on the accuracy and validity of this approach, despite some researchers reporting consistently high levels of agreement. Further, it is still not known whether blast loading can be considered deterministic, or whether it is intrinsically variable, the extent of this variability, and the range and scales over which these variations are observed. This article critically reviews historic and contemporary blast experiments, including newly generated arena tests with RDX and PETN-based explosives, with a view to demonstrating the accuracy with which blast load parameters can be predicted using semi-empirical approaches. Citation: International Journal of Protective Structures PubDate: 2023-01-05T10:50:17Z DOI: 10.1177/20414196221149752
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