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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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Authors:Obed Samuelraj Isaac, Omar Gharib Alshammari, Samuel David Clarke, Samuel Edward Rigby Abstract: International Journal of Protective Structures, Ahead of Print. Obstacles arranged into a pre-fractal shape (Sierpinski carpet) were tested for their blast attenuation abilities using 250 g PE4 at three different scaled distances (Z = 1.87, 2.24, 2.99 m/kg1/3). Three pre-fractal iterations were tested, as well as free-field tests for comparative purposes. Reductions in peak overpressure up to 26% and peak specific impulse up to 19% were observed, attributed to a mechanism known as ‘trapping’. This mechanism is characterised by a reduction in the ability of a blast wave to advect downstream, with corresponding increases in pressure observed within the bounds of the pre-fractal obstacle. Attenuation magnitudes and areas of reduced pressure and impulse were found to be drastically different with each pre-fractal iteration, with a transition from shadowing to wave trapping as the obstacles more closely resembled true fractals. A linear dependence on a newly-defined obstruction factor (OF) was found for arrival time, overpressure and impulse at the sensor locations, suggesting that the attenuation of a pre-fractal obstacle is inherently determinable. The results indicate that the mechanism of blast mitigation of pre-fractal obstacles is fundamentally different from singular or arrays of regular obstacles, and could be exploited further to develop novel protective structures with enhanced blast attenuation. Citation: International Journal of Protective Structures PubDate: 2022-12-09T08:32:22Z DOI: 10.1177/20414196221144066
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Authors:Mona Zahedi, Shahriar Golchin Abstract: International Journal of Protective Structures, Ahead of Print. Current empirical and semi-empirical based design manuals are restricted to the analysis of simple building configurations against blast loading. Prediction of blast loads for complex geometries is typically carried out with computational fluid dynamics solvers, which are known for their high computational cost. The combination of high-fidelity simulations with machine learning tools may significantly accelerate processing time, but the efficacy of such tools must be investigated. The present study evaluates various machine learning algorithms to predict peak overpressure and impulse on a protruded structure exposed to blast loading. A dataset with over 250,000 data points extracted from ProSAir simulations is used to train, validate, and test the models. Among the machine learning algorithms, gradient boosting models outperformed neural networks, demonstrating high predictive power. These models required significantly less time for hyperparameter optimization, and the randomized search approach achieved relatively similar results to that of grid search. Based on permutation feature importance studies, the protrusion length was considered a significantly more influential parameter in the construction of decision trees than building height. Citation: International Journal of Protective Structures PubDate: 2022-12-07T06:14:27Z DOI: 10.1177/20414196221144067
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Authors:Anita Bhatt, Priti Maheshwari, Pradeep Bhargava Abstract: International Journal of Protective Structures, Ahead of Print. This study presents a probabilistic analysis of a single degree of freedom (SDOF) system subjected to drift-controlled distant blast loading employing Monte-Carlo simulation using MATLAB. The simulations are achieved using an equivalent static force (ESF)–based model as the deterministic model. The loading and structural parameters are treated as random variables in the parametric sensitivity analysis. ESF factor and the resistance of the SDOF system are observed as the response parameters. ESF factor is found to be highly sensitive to positive pulse duration, whilst the resistance is found to be more sensitive to both positive pulse duration and the peak blast force. With the log-normal distribution of input parameters, the ESF factor and the resistance of the SDOF system follow the log-normal distribution. The present study suggests that the probabilistic analysis is more conservative than the deterministic analysis. The uncertainty can be incorporated in a deterministic approach for both analysis and design purposes by opting suitable factor of safety (FOS) based on probabilistic analysis. Citation: International Journal of Protective Structures PubDate: 2022-12-03T03:27:28Z DOI: 10.1177/20414196221142905
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Authors:Yeou-Fong Li, Gobinathan Kadagathur Ramanathan, Jin-Yuan Syu, Chih-Hong Huang, Ying-Kuan Tsai Abstract: International Journal of Protective Structures, Ahead of Print. Impact and blast wave loadings act as high instant energy and might cause damage to reinforced concrete infrastructures. This research aims to investigate the effect of using different length proportions of carbon fiber on the mechanical behaviors of concrete. Moreover, in this study, original carbon fiber and sizing-removed carbon fiber were added into concrete with different mix-proportions. The sizing on the carbon fiber surface was removed by using heat-treated method. In addition, the carbon fiber was dispersed by a high-pressure air compressor. Lengths of 12 mm and 24 mm carbon fibers were used in different mix-proportions to find the highest mechanical strength of carbon fiber reinforced concrete (CFRC) under a 1% fiber-to-cement weight ratio. Compressive, flexural, and impact tests were conducted on CFRC specimens. The CFRC specimen with 50% 12 mm and 50% 24 mm sizing-removed carbon fiber attained the highest impact resistance, and it also had the best performance under blast wave loading compared with the other CFRC specimens. The broken CFRC specimens were examined by an optical microscope to identify the failure mode of the carbon fibers in CFRC specimens. The addition of 50% 12 mm and 50% 24 mm sizing-removed carbon fiber can significantly improve the compressive and flexural strength of reinforced concrete. Citation: International Journal of Protective Structures PubDate: 2022-11-10T07:36:59Z DOI: 10.1177/20414196221138596
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Authors:Gaetan Ruscade, Isabelle Sochet, Karim Djafer Abstract: International Journal of Protective Structures, Ahead of Print. Nowadays, the safety of infrastructure and people is a primary concern. To ensure safety in public, industrial, or military facilities, it is necessary to be able to predict the behavior of shock waves in any environment. However, while the physical phenomena that occur in free field are well known, they cannot be applied to follow the path of a shock wave in a closed medium, where the phenomena are more complex. The aim of the present study was to define the origins of the different reflections and the path followed by the shock waves after the first reflection in a closed environment composed of two chambers separated by a wall with a variable opening. To achieve this, a fast code was developed based on the shortest path algorithm to determine the parameters of the shock wave at any point of a simple geometry. The code was designed from small-scale experiments that enabled the predictive laws of the distribution of maximum overpressure, total impulse, and the arrival times of the first four peaks to be established. An application of the code is presented in the last part of the paper. Citation: International Journal of Protective Structures PubDate: 2022-11-01T05:18:36Z DOI: 10.1177/20414196221137918
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Authors:Jack Denny, Genevieve Langdon, Sam Rigby, Alex Dickinson, James Batchelor Abstract: International Journal of Protective Structures, Ahead of Print. Explosions increasingly occur in densely populated, urban locations. Primary blast injuries (PBIs), caused by exposure to blast wave overpressure, can be predicted using injury criteria, although many are based on idealised loading scenarios that do not necessarily reflect real life situations. At present, there is limited understanding of how, and to what extent, blast-structure interaction influences injury risk, and the suitability of injury criteria that assume idealised loading. This work employed computational fluid dynamics to investigate the influence of blast interaction effects such as shielding and channelling on blast load characteristics and predicted PBIs. The validated modelling showed that blast interaction with common urban features like walls and corners resulted in complex waveforms featuring multiple peaks and less clearly defined durations, and that these alter potential injury risk maps. For example, blast shielding due to corners reduced peak overpressures by 43%–60% at locations behind the corner. However, when the urban layout included a corner and a wall structure, higher pressures and impulse due to channelling were observed. The channelling significantly increased the injury risk at the exposed location and reduced the shielding effects behind the corner. In these cases, the application and interpretation of existing injury criteria had several limitations and reduced reliability. This demonstrates that structural-blast interaction from common urban layouts has a significant effect on PBI risk. Specific challenges and further work to develop understanding and reliability of injury prediction for urban blast scenarios are discussed. Citation: International Journal of Protective Structures PubDate: 2022-10-28T08:10:38Z DOI: 10.1177/20414196221136157
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Authors:Shuoyan Zhang, Chuanbo Zhou Abstract: International Journal of Protective Structures, Ahead of Print. Subway station is usually located in the dense area of urban buildings (structures). The blasting construction of subway station foundation pit is bound to have adverse effects on adjacent buildings (structures). Therefore, it is necessary to study the dynamic response of the building (structure) and propose the safety threshold of vibration velocity. Based on the foundation pit blasting project of Hejialong Station of Wuhan Rail Transit Line 12, the vibration monitoring of the field blasting test is carried out. Combined with LS-DYNA numerical simulation software, the dynamic response characteristics of a reinforced concrete rigid frame natatorium near the foundation pit are studied, and safety thresholds for structural vibration velocities are derived. It is worth noting that the structure is a large span reinforced concrete rigid frame structure, which is different from the general reinforced concrete frame structure. The safe allowable vibration velocity in the specification is not fully applicable to the structure. Therefore, it is necessary to focus on the dynamic response of the structure under the blasting effect and propose the safety threshold of structural vibration velocity, which can provide reference for the subsequent foundation blasting. The results are as follows: Blasting seismic waves in different propagation media, their energy attenuation is different. By analyzing the vibration velocity of reinforced concrete rigid frame structures, it is found that the high-level amplification effect occurred at specific height range. In addition, the vibration velocity changes abruptly at the parts where the shape and dimensions of the rigid frame cross-section change. The peak vibration velocity and the maximum principal stress of the concrete elements were statistically analyzed to obtain the linear relationship equation, and the vibration velocity safety control threshold of the structure was predicted to be V = 5.089 cm/s. Citation: International Journal of Protective Structures PubDate: 2022-10-26T04:02:30Z DOI: 10.1177/20414196221136159
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Authors:Huazhang Cao, Nan Jiang, Yingkang Yao, Jinshan Sun, Yiwen Huang Abstract: International Journal of Protective Structures, Ahead of Print. Urban concrete pipelines are prone to damage in blasting projects such as excavation of adjacent metro tunnels. Therefore, it is necessary to evaluate the safety of buried concrete pipeline subjected to blasting vibration. Based on the field blasting test of full-scale buried concrete pipeline, considering the factor of pipeline diameter, the dynamic response of concrete pipelines with different diameters was studied by using finite element software ANSYS/LS-DYNA. According to dimensional analysis, a prediction model of particle peak velocity (PPV) considering pipeline diameter was established. Combined with the tensile strength of concrete, the safety criterions of PPV for concrete pipeline with different diameters were proposed, which provided guidance for actual blasting. Citation: International Journal of Protective Structures PubDate: 2022-10-01T03:10:02Z DOI: 10.1177/20414196221116650
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Authors:Obed Samuelraj Isaac, Omar Ghareeb Alshammari, Erik Green Pickering, Samuel David Clarke, Samuel Edward Rigby Abstract: International Journal of Protective Structures, Ahead of Print. Blast–obstacle interaction is a complex, multi-faceted problem. Whilst engineering-level tools exist for predicting blast parameters (e.g. peak pressure, impulse and loading duration) in geometrically simple settings, a blast wave is fundamentally altered upon interaction with an object in its path, and hence, the loading parameters are themselves affected. This article presents a comprehensive review of key research in this area. The review is formed of five main parts, each describing: the direct loading of a blast wave on the surface of a finite-sized structure; the modified pressure of the blast wave in the wake region of three main obstacle types – blast walls, obstacles, wall/obstacle hybrids; and finally, a brief description of some methods for predicting loading parameters in such blast–obstacle interaction settings. Key findings relate to the mechanisms governing blast attenuation, for example, diffraction, reflection (diverting away from the target structure), expansion/volume increase, vortex creation/growth, as well as obstacle properties influencing these, such as porosity (blockage ratio), obstacle shape, number of obstacles/rows, arrangement and surface roughness. Citation: International Journal of Protective Structures PubDate: 2022-09-26T11:16:36Z DOI: 10.1177/20414196221118595
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Authors:Piotr R Nowak, Tomasz Gajewski, Piotr Peksa, Piotr W Sielicki Abstract: International Journal of Protective Structures, Ahead of Print. The clearance of underwater ordnance is one of the most complex tasks entrusted to appropriately trained and equipped soldiers. State-of-the-art knowledge in this area is rarely published and is most often possessed by a narrow group of navy specialists. The aim of this paper was to find a link between the existing mathematical models for the peak pressure of underwater explosion with measurements of small charge detonations for long ranges to the observation point in real life scenarios. We have shown the results of the research in which the underwater explosion tests were presented for different TNT equivalents and standoff distances and thus distance ratios. The curves of pressure versus time of ignition were reported. The measurements were confronted with empirical formulas. The comparison showed large, but expected, differences, since the empirical formulas are advised for smaller distance ratios. Based on the conclusions from the study, the new methodology to identify the loading from underwater explosions based on a database collected was postulated. By creating a survey methodology for ships crew for recording explosion parameters, a large number of events can be registered without a strict setup of the test area. The database obtained can be used by military commanders to identify the explosive hazard in the Baltic Sea region. Citation: International Journal of Protective Structures PubDate: 2022-09-26T03:07:28Z DOI: 10.1177/20414196221120511
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Authors:Mohtady Sherif, Hesham Othman, Hesham Marzouk, Hassan Aoude Abstract: International Journal of Protective Structures, Ahead of Print. This paper presents a new material constitutive model for simulating the uniaxial material behavior of ultra-high performance fiber reinforced concrete (UHP-FRC). The model accounts for the contribution of the steel fiber content to the tensile behavior. The model variables are the fracture energy, the characteristic length, and the crack bandwidth. Thus, it guarantees a mesh size independent numerical modeling of UHP-FRC. The model is developed based on the reported results of a state-of-the-art and highly accurate experimental investigation for the uniaxial behavior of UHP-FRC. This paper also adopts the concrete damage plasticity model (CDP) as a multi-axial yield surface criterion and presents the applicability of the material constitutive model and CDP for modeling UHP-FRC under unconfined non-contact blast loading.The results of the numerical models are validated against the experimental data of shock tube testing conducted by the authors at the University of Ottawa shock tube in collaboration with Ryerson University. The results revealed that the developed material constitutive model accurately represented the uniaxial behavior of UHP-FRC. The CDP model combined with the material constitutive model developed in this study can accurately model UHP-FRC structures under unconfined non-contact blast loading. Citation: International Journal of Protective Structures PubDate: 2022-09-07T02:25:56Z DOI: 10.1177/20414196221120512
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Authors:Omar Ghareeb Alshammari, Obed Samuelraj Isaac, Samuel David Clarke, Samuel Edward Rigby Abstract: International Journal of Protective Structures, Ahead of Print. Obstructing the passage of blast waves is an effective method of mitigating blast pressures downstream of the obstacle. To this end, the interaction between a blast wave and a simplified structural shape, such as a cylinder, has been widely investigated to understand the complex flow pattern that ensues around the obstacle. The patterns include the interference zones of the incident wave, the diffracted wave, and other secondary waves in the downstream region. Such zones are responsible for causing significant modifications to the blast wave parameters. This research aims to identify and study the factors that serve to mitigate the resulting blast loads downstream of a cylindrical obstacle – both on the ground, and on a rigid wall target that the obstacle is aiming to protect. Inputs from this numerical study are also used to develop a fast-running predictive method based on an artificial neural network (ANN) model. It was found that the size of the cylinder, the strength of the blast wave, the position of the cylindrical obstruction, and the target length, all have remarkable effects on the development of the complex flow-field downstream, and on the impulse mitigation on a reflective target. A number of key mitigation mechanisms are identified, namely shadowing and interference, and their origins and significance are discussed. An ANN model trained using scaled input parameters could successfully predict impulse values on such a reflective target. Using this model to predict the response of previously unseen configurations (for the ANN) gave excellent correlation, thereby demonstrating the high fidelity of this fast-running tool, and its ability to predict the effectiveness of various wave-cylinder interactions in mitigating blast loading. Citation: International Journal of Protective Structures PubDate: 2022-09-02T08:23:11Z DOI: 10.1177/20414196221115869
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Authors:Yeou-Fong Li, Yan-Ru Huang, Jin-Yuan Syu, Ying-Kuan Tsai, Chih-Hong Huang Abstract: International Journal of Protective Structures, Ahead of Print. Reinforced concrete structures sometimes are deteriorated and damaged by seismic and blast wave loadings, and the resistance of fiber-reinforced concrete was tested at a loading of high-strain rate. Therefore, concrete structures were needed to improve the dynamic load resistance and energy absorption capabilities. In infrastructures, fiber is incorporated into concrete and is used to strengthen structures to increase its durability and resistance to high-strain rate loadings. In this study, the quasi-static and dynamic mechanical behaviors of Kevlar fiber-reinforced concrete were studied by the compressive strength test and Split Hopkinson Pressure Bar test, respectively. The 0.5% weight ratio Kevlar fiber content of KFRC specimens attained the highest strength in the quasi-static and dynamic test compared with benchmark and other 1.0%, 1.5% weight ratios. The KFRC specimens with the length of 12 mm and 24 mm exhibit similar effects in the quasi-static compressive strengths, but the KFRC specimens with the length of 24 mm fiber attained higher strain energies under dynamic loading. Citation: International Journal of Protective Structures PubDate: 2022-08-14T12:47:21Z DOI: 10.1177/20414196221118596
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Authors:Feng Yang, Nan Jiang, Chuanbo Zhou, Guopeng Lyu, Yingkang Yao Abstract: International Journal of Protective Structures, Ahead of Print. To ensure the safety and stability of adjacent underground structures is a key problem for the subway tunnel blasting construction. In this paper, there is a tunnel group (Sheshan civil air defense engineering) composed of several tunnel units right above a subway tunnel under blasting construction (Wuhan Metro Line 5). The vibration of the tunnel group induced by two blasting excavations of the subway tunnel was monitored. For further research, an effective 3D numerical model established by LS-DYNA, which was verified by field monitoring data, was used to analyze the dynamic response of the tunnel group in the whole process of the subway tunnel blasting. According to the numerical simulation results, the dynamic response characteristics of each tunnel unit were studied, and the most vulnerable area in each tunnel unit was determined. Then, the functional relationships between the maximum vibration velocities and the maximum tensile stresses of the vulnerable areas were established. Based on the maximum tensile stress criterion, the safety vibration velocity threshold of each vulnerable area was calculated using the relationship models. Furthermore, for convenient field monitoring during the subway construction, the safety vibration threshold at the floor of the tunnel group was also calculated. Lastly, to obtain the maximum charge per delay, five cut blasting with different charges were simulated. The maximum charge of the cut blasting in different stages of the subway tunnel blasting excavation was proposed. The research results of this paper have reference value for the blasting vibration safety control of similar tunnel excavation projects in the future. Citation: International Journal of Protective Structures PubDate: 2022-08-12T11:49:03Z DOI: 10.1177/20414196221119234
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Authors:Kewei Liu, Megan Walske, Mi Zhou, Xihong Zhang Abstract: International Journal of Protective Structures, Ahead of Print. The use of rammed earth (RE) as a construction material has recently received renewed interest due to its sustainability characteristics and potential for low-cost construction. Modern RE includes the addition of a binder to increase its performance. The mechanical performance of stabilised RE particularly the dynamic material properties is still not well understood. During the design life, a structure could experience dynamic loading. It is necessary to properly understand the dynamic properties of stabilised RE for safe applications. In this study, the quasi-static and dynamic material properties of cement and calcium carbonate residue (CCR) stabilised RE are experimentally investigated. The failure of the stabilised RE under different loading rates is investigated. Dynamic increase effect on cement and CCR stabilised RE are studied. The unconfined uniaxial compressive strength (UCS), Young’s modulus of the two types of stabilised RE at different strain rates are quantified. Empirical formulae of dynamic increase factor are derived for engineering application. Citation: International Journal of Protective Structures PubDate: 2022-08-12T02:22:21Z DOI: 10.1177/20414196221119239
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Authors:Qiyao Li, Li Chen, Chengjun Yue, Yuzhou Zheng, Jiayi Yuan, Xudong Chen Abstract: International Journal of Protective Structures, Ahead of Print. Concrete shrinkage usually results in the decrease in bearing capacity, durability and impact resistance of Concrete-Filled steel tube (CFST) structures during its service life. High strength expansive concrete (HSEC) is recently developed to deal with the shrinkage cracking in CFST structures. In this study, dynamic compressive tests and dynamic splitting tensile tests on the developed grade C60, C70 and C80 HSEC were performed using a split Hopkinson pressure bar device. Test results show that the expansive concrete is a typical rate-sensitive material, and its dynamic compressive strength and dynamic splitting tensile strength both increase with the strain rate. The compressive strength dynamic increase factor (DIFc) of HSEC is smaller than that of the ordinary concrete under the same strain rate, whereas the splitting tensile dynamic increase factor (DIFt) is larger than that of the ordinary concrete. All the test data were classified to establish calculation models of DIFc, peak toughness (Rp), specific energy absorption (SEA), and DIFt, which provide a theoretical basis for the design and application of HSEC and CFST in engineering. Citation: International Journal of Protective Structures PubDate: 2022-08-09T09:30:14Z DOI: 10.1177/20414196221119232
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Authors:Umur Ibrahim Cicek, Darren John Southee, Andrew Allan Johnson Abstract: International Journal of Protective Structures, Ahead of Print. This paper investigates the effect of material extruded body armour specimen size on stab penetration depth and back-face signature (BFS) and establishes the minimum thickness required for a series of material extrusion materials to provide protection against the UK Home Office Scientific Development Branch (HOSDB) body armour KR1-E1 requirements. In stage one, material extruded planar test specimens ranging from 40 × 40 mm to 80 × 80 mm in length and width with 10 mm increments at three different thicknesses, 6, 8 and 10 mm, were stab tested under 24 joules of impact energy using a gravity driven drop test apparatus. In stage two, 50 × 50 mm specimens in six material categories, PC, ABS, PLA, TPLA, PA and TPU, were manufactured at different thicknesses via material extrusion and impacted in accordance with the UK HOSDB KR1-E1 stab impact energy level as they were the optimum size when considering overall stab and BFS performance. The study established the fundamental steps towards the use of material extrusion in future personal protection solutions. Results demonstrated that stab penetration and BFS were dependent on specimen size, thickness and material type, and there was an inverse relationship between stab penetration depth and BFS. Also, a minimum thickness of 5 mm for PC and TPLA, 6 mm for ABS, 7 mm for PLA, 11 mm for PA and 12 mm for TPU, with 100% print density, was required in order to provide protection against the HOSDB KR1-E1 level of 24 J stab impact energy. Citation: International Journal of Protective Structures PubDate: 2022-06-29T04:50:05Z DOI: 10.1177/20414196221112148
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Authors:Rodrigo Mourão, Andreia Caçoilo, Filipe Teixeira-Dias, Arturo Montalva, Hollice Stone, Eric Jacques Abstract: International Journal of Protective Structures, Ahead of Print. The response of structures subject to impulsive loads remains a field of intense research. Whilst traditional construction materials, such as steel and concrete/masonry, have been the focus of most studies, further research on the performance of alternative materials for blast-resistant applications has been driven by their growing use in sustainable construction. Over the last years, engineers have been re-evaluating the use of timber as a prime construction material for a range of building types, from small office to high-rise residential buildings. As a result, there is now a growing need to study the blast resistance of timber structures, as they may become potential targets of terrorist attacks or being placed in the blast-radius of other critical buildings. A review of existing research on the blast resistance of timber structures is presented and key factors on the blast analysis and design of such structures are discussed. Most of the research has been conducted on light-frame wood stud walls, glued- and cross-laminated timber, and addresses material properties under high strain rates, typical failure modes, behaviour of structural connections and retrofitting solutions. Failure modes are reported to be highly dependent on the element layout and manufacturing aspects, and dynamic increase factors for the modulus of elasticity and maximum strength in the ranges of [1.05, 1.43] and [1.14, 1.60], respectively, have been proposed for different timber elements. Mechanical connectors play a significant role in dissipating energy through plastic deformation, as the brittle nature of timber elements compromises the development of their full capacity. Regardless the element type, SDOF models can accurately predict the dynamic response as long as idealised boundary conditions can be considered. Overall, although a good amount of research is available, more extensive research is needed to guide the design and engineering practice and contribute to the development of design codes and testing standards for timber structures under blast loading. Citation: International Journal of Protective Structures PubDate: 2022-05-30T08:11:14Z DOI: 10.1177/20414196221092466
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Authors:Emily M Johnson, Nick Grahl, Martin J Langenderfer, David P Doucet, Joseph Schott, Kelly Williams, Barbara Rutter, Catherine Johnson Abstract: International Journal of Protective Structures, Ahead of Print. Since the inception of high explosives as an industrial tool, significant efforts have been made to understand the flow of energy from an explosive into its surroundings to maximize work produced while minimizing damaging effects. Many tools have been developed over the past century, such as the Hopkinson–Cranz (H-C) Scaling Formula, to define blast wave behavior in open air. Despite these efforts, the complexity of wave dynamics has rendered blast wave prediction difficult under confinement, where the wave interacts with reflective surfaces producing complex time-pressure waveforms. This paper implements two methods to better understand blast overpressure propagation in a confined tunnel environment and establish whether scaled tests can be performed comparatively to costly full-scale experiments. Time–pressure waveforms were predicted using both a 1:10 scaled model and three-dimensional air blast simulations conducted in Ansys Autodyn. A comparison of the reduced scale model simulation with a full-scale blast simulation resulted in self-similar overpressure waveforms when employing the H-C scaling model. Experimental overpressure waveforms showed a high level of correlation between the reduced scale model and simulations. Additionally, peak overpressure, duration, and impulse values were found to match within tolerances that are highly promising for applying this methodology in future applications. Using this validated relationship, the simulated model and reduced scale tests were used to predict an overpressure waveform in a full-scale underground mine opening to within 2.12%, 2.91%, and 7.84% for peak overpressure, time of arrival, and impulse, respectively. This paper demonstrates the effectiveness of scaled, blast models when predicting blast wave parameters in a confined environment. Citation: International Journal of Protective Structures PubDate: 2022-05-25T12:52:20Z DOI: 10.1177/20414196221095252
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Authors:Md. Jahidul Islam, Tasnia Ahmed, Sheikh Muhammad Fahad Bin Imam, Muhammad Ifaz, Hamidul Islam Abstract: International Journal of Protective Structures, Ahead of Print. Steel is susceptible to corrosion and requires a significant concrete cover, which increases self-weight and cost. Therefore, an alternative to traditional reinforcements is needed. Textile reinforced concrete (TRC) is a favorable composite using textile material as reinforcement with a fine-grained concrete matrix. This study represents a comparison between different TRCs having different textile reinforcements subjected to flexural bending and impact loading. Four types of textiles—glass (GT), a square oriented galvanized iron (SGIT), diagonal pattern galvanized iron (DGIT), and carbon (CT) are used. All four types of textiles are used to prepare 400 x 50 x12 mm textile reinforced mortar (TRM) and tested for tensile strength properties. This study tests TRC panel and plate samples by three-point bending and drop-weight impact methods. The uniaxial tensile strength test of the textiles shows that CTs can take around 2.3 times higher tensile load than SGITs. However, their tensile load capacity is almost similar in the case of TRM, where SGIT textile shows about 30% higher extension. The flexural bending test of the TRC panels shows that the load-carrying ability increases nearly two times with the increase of 25 mm in thickness even when the number of reinforcement layers remains the same. With the increase in thickness, SGIT textile shows better performance. Drop-weight impact test of the TRC plates shows that the impact energy absorption in CT textile plates is up to two times higher than SGIT plates for various thicknesses. This study summarizes that CT shows overall better performance than SGIT. Citation: International Journal of Protective Structures PubDate: 2022-05-25T12:51:20Z DOI: 10.1177/20414196221095250
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Authors:Gopinath Kanakadandi, Vijayabaskar Narayanamurthy, Y V Daseswara Rao Abstract: International Journal of Protective Structures, Ahead of Print. This paper presents the structural deformation and failure of a thin domed-scored metallic disc (SMD) applied at the bottom of a pressurized rocket silo which needs to withstand a storage pressure and undergo instantaneous rupture under an impulsive pressure. Initially, the large deformation and rupture of a flat-thin SMD subjected to a pressure impulse is numerically studied and validated with experimental results. Subsequently, the behavior of a domed-thin SMD is investigated for the aforementioned loadings in the rocket silo. The influence of loading rates [math], score depth and width-to-disc thickness ratio (t1/t and b/t), diameter-to-disc thickness ratio (D/t), dome height-to-disc diameter ratio (H/D), score length-to-disc radius ratio (l/R), score pattern, and score geometry on the deformation and failure response of the domed-thin SMD is investigated. The studies demonstrate that (1) the failure initiation point shifts from 1/4th radius to the disc center for loading rates> 10 MPa/s; (2) under impulse loading, the responses are (i) sensitive to the loading rates up to 100 MPa/s, (ii) sensitive to score’s depth, only up to half the disc thickness and insensitive to score’s width, (iii) unaffected for number of scores N> 6, (iv) stabilized for l/R> 0.4, and (vii) almost the same for semi-circular, rectangular and triangular score geometries; (3) the failure do not initiate and propagate along all scores for N> 10 in the disc; and (4) behavior of the domed SMD approaches to that of a spherical dome for H/D> 0.3. Citation: International Journal of Protective Structures PubDate: 2022-05-25T12:51:04Z DOI: 10.1177/20414196221095249
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Authors:Jordan J Pannell, Sam E Rigby, George Panoutsos Abstract: International Journal of Protective Structures, Ahead of Print. Transfer learning offers the potential to increase the utility of obtained data and improve predictive model performance in a new domain, particularly useful in an environment where data is expensive to obtain such as in a blast engineering context. A successful application in this respect will improve existing surrogate modelling approaches to allow for holistic and efficient strategies to protect people and structures subjected to the effects of an explosion. This paper presents a novel application of transfer learning for the prediction of peak specific impulse where we demonstrate that previous knowledge learned when modelling spherical charges can be transferred to provide a performance benefit when modelling cylindrical charges. To evaluate the influence of transfer learning, two artificial neural network architectures were stress tested for three levels of random data removal: the first model (NN) did not implement transfer learning whilst the second model (TNN) did by including a bolt-on network to a previously published NN model trained on the spherical dataset. It is shown the TNN consistently outperforms the NN, with this out-performance increasing as the proportion of data removed increases and showing statistically significant results for the low and high threshold with less variability in all cases. This paper indicates transfer learning applications can be used successfully with considerable benefit with respect to surrogate modelling in a blast engineering context. Citation: International Journal of Protective Structures PubDate: 2022-05-24T08:59:40Z DOI: 10.1177/20414196221096699
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Authors:S.M. Anas, Mehtab Alam, Mohammad Umair Abstract: International Journal of Protective Structures, Ahead of Print. Composite structural members such as concrete-filled double-skin steel tube (CFDSST) and concrete-filled double steel tubular (CFDST) columns are increasingly being utilized in modern structures owing to their capability to integrate the beneficial properties of constituent materials to carry heavy loads as compared to conventional reinforced concrete columns. Axial compression performance of such composite columns has been extensively investigated and available in the open literature. However, their response under impulsive loadings such as those induced by explosions is not very well studied because not many investigations have been conducted on these columns. Performance of composite compression members under short-duration/high-magnitude blast loading is of considerable interest under the prevailing environment of hi-tech wars, subversive activities, and accidental explosions. The recent devastating accidental Ammonium Nitrate explosion at Beirut port (Lebanon), and the ongoing invasion of Ukraine by Russia raise the concern of researchers and engineers for the safety of structural elements/components. In this study, a 3-D finite element model of axially loaded 2500 mm long CFDSST column of ultra-high-strength concrete (170 MPa) is developed in ABAQUS/Explicit-v.6.15 computer code equipped with Concrete Damage Plasticity (CDP) model, and investigation has been carried out for its blast performance under the 50kg-TNT explosive load at a standoff distance of 1.50 m in free-air. The effects of strain rate on the compressive strength of the concrete are considered as per fib Model Code 2010 (R2010)and UFC-3-340-02 (2008). The non-linear behavior of the steel is also taken into account. Damages in the form of (1) a - concrete crushing on the explosion side of the column and b - concrete cracking on the tension side and their spread over the column length, and (2) yielding of tubes are observed. Computational results are validated with the available experimental observations. To improve the column response, the analysis has been extended to investigate the blast performance of axially loaded CFDSST columns with and without core concrete having an inner steel tube of circular/square cross-section and their response have been compared with the equivalent single skin concrete-filled steel tubular circular/square columns of same axial load capacity. Citation: International Journal of Protective Structures PubDate: 2022-05-24T06:04:49Z DOI: 10.1177/20414196221104143
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Authors:Yanchao Shi, Shaozeng Liu, Zhongxian Li, Yang Ding Abstract: International Journal of Protective Structures, Ahead of Print. Extreme explosion events result in demands for emergency rescue service. From the civil engineering perspective, a quick safety assessment of building structures in the explosion’s vicinity will provide the emergency rescue committee with concrete support to make scientific decisions. In this paper, three primary issues, namely, inverse analysis of explosive characteristics, blast wave propagation in complex urban areas and blast-induced damage identification, are reviewed. These are often performed stepwise and form a multi-step whole to assist the emergency rescue service. The paper begins by introducing the inverse analysis of explosives based on craters, building damages and seismic or acoustic records. In this step, explosive characteristics, for example, charge type, original time, yield and location, could be produced and input into blast load calculation in the next step. Then, the existing literature on blast wave propagation and blast load determination is presented with close attention to complex urban environments. It shows that the current study remains in its infancy and relies on advancement in computational fluid dynamics (CFD). Besides, pressure–impulse (P-I) diagrams which predict the structural damage based on the calculated blast loads are illustrated. Onsite damage detection techniques, such as visual inspection, non-destructive testing (NDT) and vibration-based methods, are also discussed. The paper ends with a discussion of the shortcomings of previous work and the outlooks of further work. Citation: International Journal of Protective Structures PubDate: 2022-05-23T10:21:48Z DOI: 10.1177/20414196221104146
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Authors:Adam A Dennis, Danny J Smyl, Chris G Stirling, Samuel E Rigby Abstract: International Journal of Protective Structures, Ahead of Print. Numerical analysis is increasingly used for batch modelling runs, with each individual model possessing a unique combination of input parameters sampled from a range of potential values. Whilst such an approach can help to develop a comprehensive understanding of the inherent unpredictability and variability of explosive events, or populate training/validation data sets for machine learning approaches, the associated computational expense is relatively high. Furthermore, any given model may share a number of common solution steps with other models in the batch, and simulating all models from birth to termination may result in large amounts of repetition. This paper presents a new branching algorithm that ensures calculation steps are only computed once by identifying when the parameter fields of each model in the batch becomes unique. This enables informed data mapping to take place, leading to a reduction in the required computation time. The branching algorithm is explained using a conceptual walk-through for a batch of 9 models, featuring a blast load acting on a structural panel in 2D. By eliminating repeat steps, approximately 50% of the run time can be saved. This is followed by the development and use of the algorithm in 3D for a practical application involving 20 complex containment structure models. In this instance, a ∼20% reduction in computational costs is achieved. Citation: International Journal of Protective Structures PubDate: 2022-05-17T04:28:54Z DOI: 10.1177/20414196221085720
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Authors:Chanel Fallon, Graham J. McShane First page: 3 Abstract: International Journal of Protective Structures, Ahead of Print. Elastomer coatings have been found to offer protection to structural components when subjected to dynamic load cases, such as impact and blast. One such application of interest is the protection of concrete structures. Elastomer coatings have the potential to provide a cost effective and practical protective solution. The dynamic response of quasi-brittle concrete structures to blast loading is complex, with a range of dynamic response regimes. It remains to be identified in which regimes of response an elastomer coating can offer a protective benefit. Numerical and analytical modelling of thin, one-way reinforced concrete slabs subjected to varying intensities of simulated blast loading is carried out, in order to ascertain the protective effect of an elastomeric coating. Three configurations are considered: uncoated, coated with elastomer on the blast-receiving face and coated with elastomer on the non-blast-receiving face. It is found that the slab is relatively insensitive to the elastomer coating during response regimes where concrete damage is minimal. At higher load intensities, where the slab exhibits severe damage, the numerical results indicate a substantial reduction in slab deflections may be achieved by coating on the non-blast-receiving face. At the highest loading intensities, a shift in failure mechanism is observed to one dominated by transverse shear at the supports. An analytical model quantitatively predicts a substantial coating benefit in protecting against this failure mechanism. Citation: International Journal of Protective Structures PubDate: 2022-03-27T04:21:48Z DOI: 10.1177/20414196221075821
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Authors:Vimal Kumar, Mohd. Ashraf Iqbal, Achal Kumar Mittal First page: 28 Abstract: International Journal of Protective Structures, Ahead of Print. This study is planned to explore the performance of pretensioned concrete (PC) plates under multiple impacts. A detailed investigation has been carried out on pretensioned concrete plates (0.8 × 0.8 m2) against drop impact. The plates prepared using Mix-40 and Mix-60 grade concrete have been induced with two different levels of initial prestress, that is, 1/10 and 1/5 (i.e. level-1 and level-2) times the strength of the concrete. The PC plates have been impacted by a falling impactor (2382 N) dropped from 0.5 m height. The response of those plates has been obtained and compared with the reference RC plates. The post-impact performance of the damaged plates has been further discovered by subsequently dropping the impactor multiple times from the identical height. The FE simulations of the problem have been carried out using Johnson-Holmquist-2 and metal-plasticity constitutive models for concrete and steel, respectively. The models have been initially verified with the experimental results available in literature, and subsequently the simulations for drop impact have been carried out. The simulation results are also compared with the results of drop impact experimentations performed. In general, both the pretensioned and reinforced concrete have witnessed flexural cracks at the beginning, such that pretensioned concrete witnessed lesser cracks compared to reinforced concrete. As the number of drops increased, one major splitting crack developed only in pretensioned concrete, whereas the reinforced concrete exhibited additional punching cracks. For a given concrete grade, the pretensioned concrete level-2 witnessed the smallest damage, minimal cracks, and also minimal spalling followed by the pretensioned concrete level-1 and reinforced concrete. The reinforced concrete absorbed the minimal impact energy followed by the pretensioned concrete level-1 and level-2 under the multiple impacts. The FE simulations predicted the impact force and reaction within 11.9 and 9.9% variation, respectively, with the corresponding experimental results. Citation: International Journal of Protective Structures PubDate: 2022-03-27T09:04:42Z DOI: 10.1177/20414196221078025
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Authors:İ.Kürşad Türkoğlu, Hasan Kasım, Murat Yazıcı First page: 63 Abstract: International Journal of Protective Structures, Ahead of Print. Auxiliary metamaterials designed according to the Negative Poisson’s Ratio (NPR) property are exciting structures due to their high impact strength, impact energy absorption abilities, and different damage mechanisms. These good mechanical features are suitable for aviation, automotive, and protective construction applications. These structures, whose most significant disadvantages are production difficulties, have become easier to produce with the development of 3D production technology and have been the subject of many studies in recent years. In this presented study, two conventional core geometries and three different auxetic geometries, commonly used in sandwich structures, were designed and produced with 3D printer technology. The strength and energy absorption capabilities of prototype sandwich structures investigated experimentally under bending loads with static and dynamic compression. Except for the re-entrant (RE) type core, the auxetic core foam sandwich structures demonstrate higher rigidity and load-carrying capacity than classical sinusoidal corrugated (SC) core and honeycomb (HC) core sandwich structures under both quasi-static and impact-loaded compression and three-point bending experiments. Double arrowhead (DAH) and tetrachiral (TC) auxetic cores outperformed honeycomb core in terms of specific quasi-static and impact load-bearing performance under compression by 1.5 ± 0.25 times. In three-point bending experiments under both quasi-static and impact loading conditions, the load-carrying capacity of the double arrowhead and tetrachiral auxetic cores was found to be more than 1,86 ± 0.38 times that of the honeycomb core sandwich panels. Citation: International Journal of Protective Structures PubDate: 2022-03-27T10:01:08Z DOI: 10.1177/20414196221079366
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Authors:Linghao Xiong, Nan Jiang, Chuanbo Zhou, Haibo Li First page: 87 Abstract: International Journal of Protective Structures, Ahead of Print. The connecting passage between two adjacent tunnels is conducive to the rescue and evacuation of subway tunnels when disasters occur. The blasting method is usually used in the construction of connecting passage. The vibration caused by blasting construction may endanger the safety of subway tunnel structure. As a result, the influence of blasting pressure on the stability of subway tunnel lining structure during the excavation of connecting passage is studied, and the safe blasting construction distance is proposed, which is crucial to the safety of adjacent subway tunnel lining. This study takes the connecting passage of Wuhan Metro Line 8 as an example. Using Finite element software ANSYS/LS-DYNA, an accurate numerical calculation model of construction site is established. The nonlinear elastoplastic mechanical characteristics of soil, rock, and tunnel lining are simulated by Drucker Prager, Plastic Kinematic, and Johnson Holmquist Concrete constitutive material models, respectively. The credibility of the three-dimensional numerical calculation model and material constitutive model was proved by contrasting the field measured data of the connecting passage with the numerical calculated results. Analysis of numerical results, the axial and radial PPV, frequency, and Von Mises stress of subway tunnel lining are obtained. The influence of subway tunnel lining under adjacent blasting can be obtained by analyzing the distribution law of PPV and Von Mises stress. Non-static tensile strength is needed considering the high pressure and high strain rate process of concrete during blasting. By fitting the relationship between PPV and dynamic tensile stress, and referring to DIF parameters, the safety range of PPV in subway tunnel lining blasting is determined. The critical safety distance between blasting construction and tunnel lining is obtained by Sadovsky vibration velocity attenuation formula, which is used to guide the subsequent blasting excavation of continuous tunnels. Citation: International Journal of Protective Structures PubDate: 2022-04-22T11:27:43Z DOI: 10.1177/20414196221083687
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Authors:Hamid Nikkhah, Nida Naveed, Roghaiyeh Assaedi Beiragh, Sina Dadashzadeh, Quang-Tri Truong First page: 107 Abstract: International Journal of Protective Structures, Ahead of Print. This study aims to investigate the effects of the draw beads on the crashworthiness of the aluminum tubes under axial quasi-static loading. Based on this design philosophy, a total of 12 beading tube designs with various configurations were developed. Within each design, the effect of arrangement bead form on the crashworthiness performance was also analyzed. A finite element model, validated using experimental tests, was used to study the crashworthiness performance and progressive deformation of the tubes. Based on the results, a multi-criteria decision-making method known as Technique of Order Preference by Similarity to Ideal Solution was employed to determine the most suitable tube that features high energy absorption and low impact force. The best tube with a high score was selected to investigate the effect of bead formed direction on aluminum tubes. Consequently, the study identified a bead shape tubes configuration that exhibits superior crashworthiness and low impact force. The beading tube design methodology presented in this study allows the exploitation of variable shapes geometries for the development of high-efficiency energy-absorbing structures and their crushing behaviors. Citation: International Journal of Protective Structures PubDate: 2022-05-27T12:32:28Z DOI: 10.1177/20414196221090989
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Authors:Yaniv Vayig, Zvi Rosenberg, David Ornai First page: 122 Abstract: International Journal of Protective Structures, Ahead of Print. This work deals with several issues related to the deep penetration of spherically nosed rigid projectiles impacting metallic targets at normal incidence. The most important issues in these processes are the constant resisting stress acting on the projectile beyond the initial entrance phase, the extent of the entrance phase, and the onset of cavitation at impact velocities higher than a certain threshold velocity. In this work, we derive a new relation for the target’s resisting stress in terms of its bulk and shear moduli and we also use a simplified analysis to account for the effect of the entrance phase on the depth of penetration for spherically nosed rigid projectiles. In addition, we highlight the role of cavitation in this process through numerical simulations for targets having very different densities. Citation: International Journal of Protective Structures PubDate: 2022-05-26T12:58:30Z DOI: 10.1177/20414196221092475
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