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This paper presents the nonlinear vibration analysis of a sandwich shallow shell with a honeycomb core and functionally graded graphene-reinforced skins (HCFG-GRCF) under blast load, where the core layer is composed of negative Poisson’s ratio material and the three kinds of graphene distribution patterns are considered for structural face layer. First, the material properties of functionally graded graphene platelet reinforced composite (FG-GRC) are calculated using the extended Halpin–Tsai model. Based on the First-order shear deformation theory (FSDT) along with von-Karman nonlinearity, the energy function of the shallow shells is derived. Then the direct iterative method and Newton–Raphson method are, respectively, adopted to solve the nonlinear free vibration and dynamic response in the temporal domain. The applicability and accuracy of the proposed dynamic model are verified by comparing the present results with literature solutions and Finite Element Method (FEM) results. In addition, the effects of temperature, graphene fraction, thickness ratio of core to face thickness, honeycomb cell inclined angle and boundary conditions on the dynamic response of the shallow shells are systematically analyzed. [ABSTRACT FROM AUTHOR]

Helmets exacerbate head injuries to some degree under blast load, which has been recently researched and referred to as the underwash effect. Various studies indicate that the underwash effect is attributed to either wave interaction or wave-structure interaction. Despite ongoing investigations, there is no consensus on the explanations and verification of proposed mechanisms. This study conducts experiments and numerical simulations to investigate the underwash effect, resulting from the interaction among blast load, helmets, and head models. The analysis of overpressure in experiments and simulations, with the developed simplified models that ignore unimportant geometric details, reveals that the underwash effect arises from the combined action of wave interaction and wave-structure interaction. Initially reflected in front of the head, the blast load converges at the rear after diffraction, forming a high-pressure zone. Decoupling the helmet components demonstrates that the pads alleviate rear overpressure through array hindrance of the load, resulting in a potential reduction of up to 36% in the rear overpressure peak. The helmet shell exacerbates the rear overpressure peak through geometric restriction of the load after diffraction, leading to a remarkable 388% increase in rear overpressure. The prevailing impact of the geometric restriction imposed by the shell of the helmet leads to a significant 57% increase in overpressure when employing a complete helmet. [ABSTRACT FROM AUTHOR]

For the first time, the isogeometric analysis (IGA) approach is used to model and analyze free and forced vibrations of doubly-curved magneto-electro-elastic (MEE) composite shallow shell resting on the visco-Pasternak foundation in a hygro-temperature environment. The doubly-curved MEE shallow shell types include spherical shallow shell, cylindrical shallow shell, saddle shallow shell, and elliptical shallow shell subjected to blast load are investigated. The Maxwell equation and electromagnetic boundary conditions are used to determine the vary of the electric and magnetic potentials. The MEE shallow shell's equations of motion are derived from Hamilton's principle and refined higher-order shear theory. Then, the IGA method is used to derive the laws of natural frequencies and dynamic responses of the shell under various boundary conditions. The accuracy of the model and method is verified through reliable numerical comparisons. Aside from this, the impact of the input parameters on the free and forced vibration of the doubly-curved MEE shallow shell is examined in detail. These results may be useful in the design and manufacture of military structures such as warships, fighter aircraft, drones and missiles. [ABSTRACT FROM AUTHOR]

The design of suspension bridges predominantly emphasizes wind and earthquake loads, frequently overlooking the consideration of extreme events in the design stage, thus posing a threat to bridge safety. The purpose of this research is to spread awareness among engineers for identifying weak zones in a bridge and to provide a new insight into how much damaging the blast loading could be for the long-span suspension bridges if not designed properly under the blast loads. The current dynamic analysis procedures for bridges under blast loads are complex and computationally expensive, making them unsuitable, especially for long-span bridges. To address this, a simplified dynamic analysis approach is proposed to assess the structural response and extreme limit state of suspension bridges exposed to blast loads. The method involves a bilayer solution: blast loading is modeled as nodal loads, and the structural aspect is represented by a three-dimensional (3D) fishbone skeleton finite-element (FE) model. Time-history simulations of blast loads are conducted for various bridge locations and explosive sizes. The parametric dynamic analysis reveals that the tower top node is the most vulnerable location in the suspension bridge under blast loads, which potentially exceeds the stress limits of nearby main cable elements and triggers the zipper-type progressive failure of the entire suspension bridge. Similarly, blasting at the deck nodes nearby tower on the main span side as well as on the side span side significantly amplifies axial stresses in nearby suspenders and the main cable, i.e., demand-to-capacity ratios of C18 and C19 surpass unity under BS4-6W and BS4-8W, respectively confirming that the failure state has reached for C18 and C19 under medium- to large-sized explosives. Therefore, it is recommended that the maximum demand-to-capacity ratio for all bridge components under medium- to large-sized explosives shall be kept below 0.8 to ensure the safety of the entire structure under extreme limit state. Practical Applications: This paper provides a methodology to investigate the structural redundancy of suspension bridges under extreme limit state by providing a bilayer solution: the blast aspect, which is simulated as nodal loads on the bridge road surface and the structural aspect, is simulated as a 3D fishbone skeleton FE model. The implicit dynamic analysis approach is adopted parametrically by considering variable explosive weights and locations. For each blast scenario, the time-history of nodal loads is applied to various locations of the bridge considering small- to large-sized blasts. From a practical viewpoint, this study is relevant to develop comprehensive understanding of the dynamic behavior exhibited by long-span bridges when subjected to extreme loading scenarios. In essence, the aim is to explore the benefits and applicability of this research to the design of long-span bridges under blast loading conditions. The simplified approach presented in this paper, along with the corresponding bridge response results, allows a bridge design engineer to analyze a suspension bridge effortlessly. This method eliminates the need for intricate computations required to assess blast pressure over a solid bridge model, enabling a straightforward visualization of the anticipated behavior under blast loading. The research serves a crucial role in checking and verifying the extreme limit state, in addition to assessing the serviceability and ultimate limit states according to AASHTO's requirements. For existing suspension bridges, the study proves beneficial in formulating a comprehensive blast-resistant plan through retrofitting and strengthening identified weak zones. Consequently, this research holds practical significance, serving as a foundation for further exploration and investigation into the effects of blast loading on various types of long-span bridges. [ABSTRACT FROM AUTHOR]

Hybrid composite honeycomb sandwich structures (HCHSS) were employed due to high specific strength and stiffness and higher impact resistance property required for the aerospace and defence fields. The numerical modelling of the efficient HCHSS was developed for the core, front and back face plate using the C3D8R elements to determine the realistic failure behaviour for the honeycomb sandwich structure. The ConWep blast simulation loading was applied for the HCHSS. Advanced composite materials were used for the blast analysis of the HCHSS (carbon/epoxy, graphite/epoxy, woven basalt fibres/polypropylene and woven Kevlar fibres/polypropylene). The damage initiation and damage propagation based progressive damage modelling was developed and implemented in the VUMAT code for composite materials to determine the actual failure behaviour of the HCHSS. The face sheets used in this model were of a stainless-steel alloy AL-6XN. The sandwich structure was subjected to blast loads of 1, 2 and 3 kg of TNT and their performance was compared w.r.t both front and back-face deflection. The effectiveness of sandwich panels was further examined by altering the thickness of the core. Fibre-metal laminates (FML) were used in place of the steel face sheets in the panel in order to minimise its mass, and a thorough analysis of the panel's mass in relation to its peak deflection was carried out. Upon analysing the results, it was noted that the panel with the basalt fibre reinforced polymer (BFRP) core gave the best results compared to other composite materials. For a blast load of 3 kg TNT, the peak back face deflection (PBFD) of HCHSS with a BFRP core decreased by 10.64%, 7.61% and 4.75%, respectively, compared to panels with CFRP, GFRP, and KFRP cores. The peak deflection of the panel decreased as the BFRP core thickness increased. The energy absorption capacity of the panel also increased with increasing thickness. Additionally, it was found that panels with BFRP cores and KFRP-steel laminate face sheets provided the optimum balance of strong blast resistant performance and light weight. Compared to the metallic (steel) sandwich panel, the mass of the sandwich panel with KFRP-steel laminate face sheets and BFRP core was reduced by 33%, but at the same time, its PBFD increased by almost 50%. [ABSTRACT FROM AUTHOR]

The non-uniform distributed pressure of impact wave is usually simplified into concentrated or uniform load equivalently in the optimization design of constrained layer damping structure. However, for the thin-walled structure, it becomes necessary to regard the load as a non-uniform distribution. In this paper, a topology optimization approach is proposed considering the blast load with non-uniform distribution, aiming to unveil its impact on optimization layouts and dynamic responses. Initially, the smoothed particle hydrodynamics (SPH) algorithm is used to obtain the blast pressure what are extracted and integrated into the optimization model. Subsequently, the relative density is regarded as design variable. The construction of material penalty model and the topology optimization model are based on polynomial interpolation scheme (PIS). The sensitivity of objective function is deduced employing an improved adjoint variable method (AVM) to fit the load forms, and the Newmark- β method is used to calculate the dynamic response. The optimization criterion (OC) is adopted to update the design variables. Finally, two numerical examples are used to exhibit the validity and accuracy of the presented methodology. The findings indicate that the distributed form, spread velocity, excited position and excited amplitude of the blast load all exert a notable influence on optimization results and dynamic response. These results underscore the valuable engineering application of this research and introduce a fresh perspective to the challenge of topology optimization under the blast case. [ABSTRACT FROM AUTHOR]

The present study investigates the stability of a tunnel subjected to blast loads. The tunnel is placed in a transversely isotropic rock mass. Numerical simulations are performed using the discrete-element method. The rock material between the bedding planes/joints is discretized as Voronoi polygons. The research focuses on the significance of discretizing the rock material between the bedding planes as Voronoi polygons for studying a tunnel's stability under blast loads. To this end, the influence of Voronoi polygon size, joint spacing, anisotropy angle, cover depth, and earth pressure coefficient on the tunnel response are examined. The tunnel response is measured in terms of normalized crown displacement. The study provides many novel insights that can be used to improve the design of rock tunnels. It is found that it is vital to discretize rock grains as Voronoi blocks for studying the tunnel response. When Voronoi blocks are considered, the tunnel stability increases for anisotropy angles 30° and 60° but decreases for angles 0° and 90° when no Voronoi blocks are used. The tunnel becomes more vulnerable to damage as the Voronoi block size increases. It is noted that the joint spacing and Voronoi block size are interlinked, and their influence must be considered together for assessing the tunnel stability. When joint spacing is kept twice or more than the Voronoi size, the crown displacement is higher than when joint spacing is equal to or closer to the Voronoi size. It is observed that the crown displacement is maximum when the earth pressure coefficient equals 2. Therefore, the influence of change in the earth pressure coefficient is considered the most severe of all the parameters studied. [ABSTRACT FROM AUTHOR]

In scale-down tests of ship structures subjected to a blast load, the accuracy of the predicted response of a prototype is affected by the material substitution and geometric distortion between a scaled model and a full-size structure; this is known as incomplete similarity. To obtain a more accurate response from a prototype during small-size tests, a corrected method for scaling the response of thin plates and stiffened plates under a blast load was derived. In addition, based on numerical simulations of explosion responses by employing the elastic–plastic model and the Johnson–Cook constitutive model, it was found that using the average yield stress derived from the equivalent plastic strain energy in the ideal elastic–plastic model can obtain consistent structural responses. Moreover, a method for calculating the distortion factor caused by the yield stress of different materials was proposed. Furthermore, it was demonstrated that the average effective plastic strain between the prototype and the corrected model is equal, and based on this, a similarity prediction method was established to correct the distortions caused by yield stress and the thickness of blast loaded plates. The results indicate that the proposed correction method can compensate for the differences caused by distorted factors of yield stress and thickness, with the maximum error in the structure's peak displacement being less than 3%. [ABSTRACT FROM AUTHOR]

For the first time, the isogeometric analysis (IGA) approach is used to model and analyze free and forced vibrations of doubly-curved magneto-electro-elastic (MEE) composite shallow shell resting on the visco-Pasternak foundation in a hygro-temperature environment. The doubly-curved MEE shallow shell types include spherical shallow shell, cylindrical shallow shell, saddle shallow shell, and elliptical shallow shell subjected to blast load are investigated. The Maxwell equation and electromagnetic boundary conditions are used to determine the vary of the electric and magnetic potentials. The MEE shallow shell's equations of motion are derived from Hamilton's principle and refined higher-order shear theory. Then, the IGA method is used to derive the laws of natural frequencies and dynamic responses of the shell under various boundary conditions. The accuracy of the model and method is verified through reliable numerical comparisons. Aside from this, the impact of the input parameters on the free and forced vibration of the doubly-curved MEE shallow shell is examined in detail. These results may be useful in the design and manufacture of military structures such as warships, fighter aircraft, drones and missiles.

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties and environmental resilience. Biological composite structures with helicoidal schemes and designs have remarkable capacities to absorb impact energy and withstand damage. However, there is a dearth of extensive study on the influence of fiber redirection and reorientation inside the matrix of a helicoid structure on its mechanical performance and reactivity. The present study aimed to explore the static and transient responses of a bio-inspired helicoid laminated composite (B-iHLC) shell under the influence of an explosive load using an isomorphic method. The structural integrity of the shell is maintained by a viscoelastic basis known as the Pasternak foundation, which encompasses two coefficients of stiffness and one coefficient of damping. The equilibrium equations governing shell dynamics are obtained by using Hamilton's principle and including the modified first-order shear theory, therefore obviating the need to employ a shear correction factor. The paper's model and approach are validated by doing numerical comparisons with respected publications. The findings of this study may be used in the construction of military and civilian infrastructure in situations when the structure is subjected to severe stresses that might potentially result in catastrophic collapse. The findings of this paper serve as the foundation for several other issues, including geometric optimization and the dynamic response of similar mechanical structures.

Studies on cable-stayed bridges exposed to blast loads encounter significant challenges arising from the complex interaction among different structural elements. Despite extensive investigation into how buildings respond to explosive loads, there is limited literature on the dynamic response of prestressed concrete bridge decks to blast loads. Single plane cable stayed bridges are very sensitive to cable loss or degradation. This study investigates the response of a prestressed concrete cable-stayed bridge with a single plane under blast loads, utilizing a comprehensive Finite Element (FE) model that incorporates nonlinear effects. The investigation considers blast weights of 230 kg, 680 kg, and 2270 kg of TNT. The analysis reveals that even small explosions cause damage to the deck, with more significant effects observed under higher blast loads, resulting in a damaged region measuring 12 m x 10 m with a 2270 kg TNT weight. Forces in cables near the detonation point increase by 19% during a 2270 kg TNT explosion. Notable changes are observed in pylon moments under different explosion charges. Maximum Bending Moment (BM) values are observed at the base under dead loads, while BMs at mid-height increase under various blast weights, with no discernible change at the base. This study provides valuable insights for designers, emphasizing the importance of incorporating explosion-resistant design principles into cable-stayed bridges.

In order to ascertain how explosive load influences orthotropic slabs with short span stiffeners partially positioned in the x-direction, the purpose of this study is to perform a numerical analysis. The maximum displacement of a floor surface with respect to the force of an explosive load and the angle of inclination. It is feasible to calculate the impact of the angle of inclination and the height of the blast load on the vertical deflection of the slab using the 6th order polynomial blast equation, as long as the local blast load is positioned in the center of the slab. An analysis reveals that the vertical deflection of the slab is affected by the timing of the explosion. Specifically, a more powerful explosion has a diminishing effect on the deflection of the slab. The inclination angle has no major impact on the outcomes of deflection.

• Build a mathematical model for magneto-electro-elastic cylindrical shells with geometrical imperfection. • Consider the impacts of the electrical potential, magnetic potential and thermal factor. • Illustrate the nonlinear transient responses of magneto-electro-elastic cylindrical shells. • Reveal the roles of the coupled multi-physics fields. Exploring the nonlinear mechanical behaviors of structures under external excitation is significant. This article, for the first time, attempts to demonstrate the transient response of imperfect magneto-electro-elastic (MEE) cylindrical shells under pulse load in thermal environment by time history curves and phase trajectories. Using Love's thin shell theory and Maxwell's equations, expressions for displacement-, electric-, and magnetic- fields are obtained. Combining Hamiltonian principle and Galerkin method, the nonlinear dynamic equations of cylindrical shells are derived, and Runge-Kutta method is employed to solve the whole problem. Subsequently, the transient responses under various parameters including BaTiO 3 vol fraction, geometric imperfection, electrical potential, magnetic potential, prestress, viscoelastic foundation, positive phase duration, damping coefficient, maximum blast load, geometrical parameter, temperature variation and various pulse loads are presented in numerical analysis in the forms of time history curves and phase trajectories. Finally, the conclusion advocates that the BaTiO 3 vol fraction, geometric imperfection and dimensions of cylindrical shells have significant impacts on the transient response. [ABSTRACT FROM AUTHOR]

The current work provides the comparative study based on nonlinear dynamic responses and damping performance of the viscoelastic core-based sandwich (SW) plates subjected to blast load. The 0–3 viscoelastic composite (VEC), pure/conventional viscoelastic material (VEM), and viscoelastic particulate composite (VEPC) are taken individually as the viscoelastic core within SW plate. The governing equation of motion (GEM) of the overall SW plate is formulated by following layer wise theory and fraction order derivative viscoelastic model in finite element framework. The numerical solutions are obtained by solving the GEM with the conjunction of Newmark time integration scheme and direct iteration method. The effect of various boundary conditions, geometric parameters of 0–3 VEC, particulate volume fraction in VEPC are considered on dynamic responses and damping performance of SW plate. The numerical solutions disclose that 0–3 VEC and VEPC provide the significant damping compared to conventional VEM for passive damping control of SW plates subjected blast loads. [ABSTRACT FROM AUTHOR]

This paper investigated the blast behavior of a low‐rise composite steel structure of three stories subjected to internal and external explosions for the same explosive charge of 250 kg TNT. A comparison of three various blast scenarios is aimed at better understanding how blast waves propagate in confined risk zones and their damage effects on far and exposed elements to an explosive charge. Evaluation of the damage level and the overall response of the proposed numerical model is done by estimating the adequacy of structural members subjected to blast loading using general limits in attempting to check the structure's strength and regularity. The analysis was based on load combinations and damage criteria according to the Unified Facilities Criteria which are general design approaches suitable for civil design applications in forecasting blast loads and structural system responses. The overall behavior of this structure was simulated based on a dynamic analysis by the direct simulation approach, which was chosen for modeling blast loads using the Friedlander blast load equation, and the simpler, less expensive, more accurate, and realistic A.T.‐BLAST model to deduce the simplified blast‐wave overpressure profile. The material nonlinearity at a high strain rate using the Johnson‐Cook strength and concrete plasticity damage model is studied dynamically using ABAQUS finite element code to simulate the explicit dynamic nonlinear analysis. The overall response of the proposed numerical model was evaluated by estimating the adequacy of structural members, considering the blast load as the initial cause of failure, such as axial plastic strain, internal forces limits, maximum deformation, support rotation, demand‐capacity‐ratio (DCRshear/moment), drift index and material damage model. The position of the explosive charge played an important role in determining the rate at which the structural element begins to plastic strains, displacements, moments, or rotations beyond the limits, and then key elements should be considered in structural design against progressive collapse. Results showed that steel members exhibit early indicators of failure, such as buckling necking, shear tearing, or plastic hinges, whereas concrete slabs break up immediately due to brittleness. DCRmoment values successfully showed the columns in which the first plastic joint can occur, whereas DCRshear values signaled the onset of shear failure at connections. Besides, plastic hinges played an important role in dissipating energy and preventing total structural collapse via the Strong Column‐Weak Beam design concept, which appears repeatedly in this study. The structure is a well‐designed and ductile building capable of supporting higher loads and is considered to be repairable and intact. [ABSTRACT FROM AUTHOR]

Studies on cable-stayed bridges exposed to blast loads encounter significant challenges arising from the complex interaction among different structural elements. Despite extensive investigation into how buildings respond to explosive loads, there is limited literature on the dynamic response of prestressed concrete bridge decks to blast loads. Single plane cable stayed bridges are very sensitive to cable loss or degradation. This study investigates the response of a prestressed concrete cable-stayed bridge with a single plane under blast loads, utilizing a comprehensive Finite Element (FE) model that incorporates nonlinear effects. The investigation considers blast weights of 230 kg, 680 kg, and 2270 kg of TNT. The analysis reveals that even small explosions cause damage to the deck, with more significant effects observed under higher blast loads, resulting in a damaged region measuring 12 m x 10 m with a 2270 kg TNT weight. Forces in cables near the detonation point increase by 19% during a 2270 kg TNT explosion. Notable changes are observed in pylon moments under different explosion charges. Maximum Bending Moment (BM) values are observed at the base under dead loads, while BMs at mid-height increase under various blast weights, with no discernible change at the base. This study provides valuable insights for designers, emphasizing the importance of incorporating explosion-resistant design principles into cable-stayed bridges. [ABSTRACT FROM AUTHOR]

In the protective engineering field, close-range explosions produce more energy and are more likely to cause severe damage to building structures than long-range explosions. In current standards, close-range explosions are defined as an explosion with a scale distance of less than 1.2 m/kg1/3. Besides, the steel plate's dynamic response is critical, especially under the blast loads generated by different shapes of explosives. For cylindrical explosives most commonly used in military and engineering, this study carried out experimental and numerical simulation studies on steel plates under the close-range air blast loads generated by different H/D cylindrical explosives (0.5≤H/D≤3.0). First, close-range air blast load tests were performed to study the failure modes of steel plates at different scale distances. The height-to-bottom diameter H/D ratio was defined as the shape factor of cylindrical explosive, and the effect of H/D on the failure deformation and dynamic response of the steel plate was quantitatively studied. Finally, the characteristics of shock waves generated by cylindrical explosives with different H/D were analyzed to determine the influence of H/D on the spatial distribution of shock waves. The results showed that with the increase of H/D , the steel plate deformation and damage gradually decreased. When the scale distance was more significant than or equal to 0.38, there was no crack in the steel plate, and the residual deflection gradually reduced with the increase of H/D. Despite the different scale distances, the residual deflections showed similar trends with increasing H/D. When the scale distance was less than or equal to 0.30, the steel plate cracked, and the crack area gradually decreased with increased H/D. [ABSTRACT FROM AUTHOR]

The increasing use of innovative materials in blast- and impact-resistant structures underscores the demand for robust simulation and design methods. Concrete, especially Ultra High Performance Fiber Reinforced Concrete (UHPFRC), has emerged as a key player in this domain. The present study delves into the damage investigation and dynamic response assessment of blast loaded UHPFRC panels with optimized mixture design (microsilica content, water curing conditions, and fibre proportions). The so-assembled UHPFRC material is calibrated and validated, adjusting parameters from experimental results addressing the tensile and compressive behaviours of material based on standard experimental methods. The investigation navigates through experimental and numerical challenges, emphasizing the limitations of applying available models to UHPFRC, and necessitates recalibration for optimal alignment with experimental results. An in-depth numerical analysis using LS-DYNA software is also carried out, aiming to understand the dynamic behaviour of UHPFRC panels under blast loading and performing a comparative analysis between UHPFRC and normal strength concrete (NSC) panels with and without reinforcement, emphasizing the superior performance of UHPFRC. Furthermore, the study addresses the importance of determining the minimum thickness for UHPFRC panels as protective barriers. This involves a specific strategy based on regulations and considering minimal damage to the panel, leading to the proposal of an empirical formulation. Additionally, a sensitivity analysis has been conducted to identify the influential parameters on the response of the panel. The findings of this study revealed that modelling the UHPFRC material using finite element analysis and employing advanced material models yield promising outcomes. Moreover, the proposed empirical formulation demonstrates a good level of accuracy and efficiency in predicting the minimum thickness for UHPFRC panels under blast conditions. The results of the sensitivity analysis also indicate that explosive charge weight, standoff distance, and panel thickness are the most critical parameters. These insights contribute to a comprehensive understanding of UHPFRC dynamic behaviour in blast conditions, offering valuable considerations for future applications and design implementations in this evolving field.

This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load. Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber. The exterior is supported by a Kerr elastic foundation with three characteristics. The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer. In contrast to previous first-order shear deformation theories, no shear correction factor is required. Navier’s exact solution was used to treat the double-curved shell problem with a single title boundary, while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements. To ensure the accuracy of these results, a thorough comparison technique is employed in conjunction with credible statements. The problem model’s edge cases allow for this kind of analysis. The study’s findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads. In addition, this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.

Masonry walls are commonly preferred in the construction of low-rise buildings due to their proven efficiency in resisting gravity loads and their relatively low material and labor costs. However, few studies investigating the behavior of retrofitted buildings under blast loading have been found in the literature. This paper describes the first comprehensive study investigating the efficiency of four retrofitting techniques for a low-rise masonry building under blast loading. The investigated retrofitting materials were textile-reinforced mortar (TRM), carbon-fiber-reinforced polymers (CFRPs), glass-fiber-reinforced polymers (GFRPs), and polypropylene bands (PPBs). Compared with regular reinforcing steel, these materials have light weight, high corrosion resistance, and perfect durability properties, in addition to their ease of application. A three-dimensional applied element model (AEM), which accounts for both geometric and material nonlinearities, was developed and validated to analyze an existing four-story masonry building under blast loading. Material nonlinearity was considered by including nonlinear models for masonry, mortar, TRM, CFRPs, and PPBs. Masonry blocks were modeled using brick elements, while the in-between mortar was modeled using spring elements. Validation of the AEM was by modeling masonry walls taken from the literature and comparing their results with counterparts obtained from experiments from the literature. Cracking pattern, displacements, support rotation, and load capacity for the investigated building with and without retrofitting using the four materials were compared. Costs were compared based on market prices. Retrofitting the case study building with TRM, CFRPs, GFRPs, and PPBs reduced maximum support rotation by 39%–98%, 28%–88%, 33%–92%, and 9%–84%, respectively, and increased blast load capacity by 35%–404%, 48%–91%, 83%–135%, and 26%–46%, respectively. The study revealed that retrofitting the investigated building with TRM provided the optimum behavior in terms of cost, crack propagation, and blast load capacity. Masonry walls are frequently used in low-rise buildings due to their efficiency in resisting gravity loads and having low material and labor costs. This study investigated the efficiency of textile-reinforced mortar (TRM), carbon fiber–reinforced polymers (CFRPs), glass fiber–reinforced polymers (GFRPs), and polypropylene bands (PPBs) to improve the resistance of low-rise buildings to blast loading. The adopted retrofitting materials have light weight, high corrosion resistance, and perfect durability properties. A numerical model analyzed an existing four-story masonry building under blast loading. Cracking, displacements, support rotation, and load capacity with and without retrofitting were compared. Costs were compared based on market prices. Retrofitting the studied building with TRM, CFRPs, GFRPs, and PPBs reduced maximum support rotation by 39%–98%, 28%–88%, 33%–92%, and 9%–84%, respectively, and increased blast load capacity by 35%–404%, 48%–91%, 83%–135%, and 26%–46%, respectively. The study findings recommend TRM in retrofitting masonry buildings to achieve the least cost and the fewest cracks in addition to the highest blast load resistance. [ABSTRACT FROM AUTHOR]

The stochastic response of multi-story buildings isolated by laminated rubber bearing (LRB), lead-rubber bearing (N-Z system), friction pendulum system (FPS), and resilient-friction base isolator (R-FBI) is investigated under the independent multi-hazard scenario of earthquake ground motion (EQGM), wind load (WL), and blast-induced ground motion (BIGM), which are considered as uncertain inputs. A polynomial regression-based Monte Carlo simulation (PRBMCS) is proposed to enable computationally efficient fragility assessment of base-isolated buildings. The suitability of the PRBMCS for stochastic assessment of the base-isolated buildings is compared with the conventional Monte Carlo simulation (MCS), response surface method (RSM) and Cloud analysis. The fragility curves obtained using the PRBMCS are in good agreement with that of the MCS relatively. The study includes: the effects of the characteristic parameters of the four base isolators on the fragility of the base-isolated buildings under the three hazards; influence of the extent of uncertainty in the excitations; and comparison of fragilities of the base-isolated and fixed-base buildings. Notably, the influences of characteristic parameters of the isolators on the fragility of the base-isolated buildings are different under the three hazards. The differences in the stochastic behaviour under the different hazards could have contradictory influences on the selection of isolation parameters. [ABSTRACT FROM AUTHOR]

In scale-down tests of ship structures subjected to a blast load, the accuracy of the predicted response of a prototype is affected by the material substitution and geometric distortion between a scaled model and a full-size structure; this is known as incomplete similarity. To obtain a more accurate response from a prototype during small-size tests, a corrected method for scaling the response of thin plates and stiffened plates under a blast load was derived. In addition, based on numerical simulations of explosion responses by employing the elastic–plastic model and the Johnson–Cook constitutive model, it was found that using the average yield stress derived from the equivalent plastic strain energy in the ideal elastic–plastic model can obtain consistent structural responses. Moreover, a method for calculating the distortion factor caused by the yield stress of different materials was proposed. Furthermore, it was demonstrated that the average effective plastic strain between the prototype and the corrected model is equal, and based on this, a similarity prediction method was established to correct the distortions caused by yield stress and the thickness of blast loaded plates. The results indicate that the proposed correction method can compensate for the differences caused by distorted factors of yield stress and thickness, with the maximum error in the structure’s peak displacement being less than 3%.

The U-steel support structures of underground caverns are prone to instability and failure under blast loads. The purpose of the underground cavern reinforcement is to mobilise the self-supporting capacity of the surrounding rock to resist the blast. To better understand the mechanical performance and failure mechanism of the U-steel support, the fracture process and vibration behaviour of the support structure under blast loading are investigated by the microseismic monitoring experiment. The dynamic responses of the cavern support structures under blast loading are investigated, and the potentially hazardous sections of the U-steel support structure are revealed by the theoretical analysis. The microseismic monitoring results show that the blast induced microseismic events are concentrated in the arch shoulder of the small chaînage, correspondingly the U-steel structures in this region have been partially extruded and deformed. The failure mechanism of the supporting structure is presented. In order to effectively inhibit the internal fracture evolution or macroscopic failure of the rock mass, the synergetic reinforcement scheme of the structures is proposed. The results of the research can be used as a reference for the design and control method of the U-steel support in similar projects. [ABSTRACT FROM AUTHOR]

Frequent unintentional explosions in industrial facilities and deliberate demolition of commercial buildings have resulted in significant financial damages, leading to increased demands on structural engineers to enhance blast resistance design methods. Therefore, comprehending the impact of blasts on structure performance is crucial. The study examined how a standard 21-storey reinforced concrete building structure responded to blast loads from TNT explosives of varying charge weights (100, 300, and 500 kg) at different standoff distances (10, 20, and 30 m). The research focused on the effects of structural walls at the core as well as peripheral infill walls. Using a three-dimensional finite element approach with nonlinear dynamic analysis via SAP2000 software based on Indian Standard specifications (IS:4991, 1968), key response parameters such as acceleration, displacements, and velocities were analyzed over time. It was observed that acceleration and velocity reached peak values earlier than displacement. The building's blast resistance with structural walls was deemed satisfactory; furthermore, it improved with the installation of infill walls. [ABSTRACT FROM AUTHOR]

This study systematically investigates the mechanical properties of polyurea-coated auxetic honeycomb sandwich panels under explosive load. First, the dynamic deformation process, deformation/destruction modes, maximum deflection, and energy absorption capacity of structures with different coating methods are studied and compared with uncoated structures. Based on this, the influence of polyurea coating thickness, blast center distance, and explosive mass on the anti-explosion capability of sandwich panels with optimal coating positions is investigated. Finally, performance optimization design of the sandwich panel with optimal coating position is carried out. The results indicate that polyurea coating is beneficial for improving the explosion resistance of sandwich panels, and the back side coated sandwich panel (type B) has the best blast resistance. When other variables of the sandwich panel remain unchanged, increasing the thickness of the polyurea layer may effectively suppress the maximum deflection. Meanwhile, increasing the distance between explosion centers and reducing the mass of explosives can significantly reduce the degree of damage to sandwich panels. Compared with the baseline model, the optimized structure shows a 17.9% reduction in the maximum backside deflection and a 66.1% increase in the specific energy absorption. This research provides a potential new way to enhance the explosion resistance of metal sandwich panels. [ABSTRACT FROM AUTHOR]

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Abstract To evaluate the stability of a lined rock cavern (LRC) for compressed air energy storage (CAES) containing a weak interlayer during blasting in the adjacent cavern, a newly excavated tunnel-type LRC was taken as the research object. By combining similar model tests and numerical simulation, the dynamic responses and deformation characteristics of the LRC for CAES under joint action of factors including the gas storage pressure, weak interlayer, and blast load were studied. The influences of the thickness, dip angle, and location of the weak interlayer on deformation of the LRC were discussed. The results show that as the gas storage pressure increases, the rate of change in strains in regions of the LRC near the weak interlayer is accelerated, and the gas storage pressure more significantly influences the sealing layer and lining than the surrounding rocks. The presence of the weak interlayer causes stress concentration in the LRC and increases the circumferential strain and residual strain of the LRC. Under the blast load, the right-side wall of the LRC shows the poorest stability, and the presence of the weak interlayer results in the energy loss in the propagation process of stress waves and an increment of peak strain in regions of the LRC around the interlayer. When the weak interlayer is separated from the LRC, as the thickness of the weak interlayer increases, the confinement of surrounding rocks at the interlayer on the LRC reduces and the circumferential strain increases. As the dip angle of the interlayer increases, the peak strain in the right upper side of the LRC grows significantly. As the distance from the weak interlayer to the LRC boundary increases, the circumferential strain in regions of the LRC near the interlayer decreases significantly. If the distance is less than 0.2r, the increment of the distance significantly affects the peak strain.

In this paper, UR50 ultra-early-strength cement-based self-compacting high-strength concrete slabs (URCS) have been subjected to contact explosion tests with different TNT charge quality, aiming to evaluate the anti-explosive performance of URCS. In the experiment, three kinds of ultra-early-strength cement-based reinforced concrete slabs with different reinforcement ratios and a normal concrete slab (NRCS) were used as the control specimen, the curing time of URCS is 28 days and 24 h respectively. The research results show that URCS has a stronger anti-explosion ability than NRCS. The failure mode of URCS under contact explosion is that the front of the reinforced concrete slab explodes into a crater, and the back is spall. With the increase of the charge, the failure mode of the reinforced concrete slab gradually changed to explosive penetration and explosive punching. The experiment results also show that the reinforcement ratio of URCS has little effect on the anti-blast performance, and URCS can reach its anti-blast performance at 28 days after curing for 24 h. On this basis, the damage parameters of URCS for different curing durations were quantified, and an empirical formula for predicting the diameter of the crater and spalling was established.

The U-steel support structures of underground caverns are prone to instability and failure under blast loads. The purpose of the underground cavern reinforcement is to mobilise the self-supporting capacity of the surrounding rock to resist the blast. To better understand the mechanical performance and failure mechanism of the U-steel support, the fracture process and vibration behaviour of the support structure under blast loading are investigated by the microseismic monitoring experiment. The dynamic responses of the cavern support structures under blast loading are investigated, and the potentially hazardous sections of the U-steel support structure are revealed by the theoretical analysis. The microseismic monitoring results show that the blast induced microseismic events are concentrated in the arch shoulder of the small chainage, correspondingly the U-steel structures in this region have been partially extruded and deformed. The failure mechanism of the supporting structure is presented. In order to effectively inhibit the internal fracture evolution or macroscopic failure of the rock mass, the synergetic reinforcement scheme of the structures is proposed. The results of the research can be used as a reference for the design and control method of the U-steel support in similar projects.

This paper presents a summary of experimental research on the performance of blast-resistant window anchors and the development of a design procedure for the anchors. The experimental results, obtained from forty-six window tests conducted under simulated blast loading using a shock tube are reported. Two analysis procedures that were developed for anchor design are described. The first procedure involves a two-degree-of-freedom dynamic analysis. The second procedure involves a single degree of freedom analysis that can be implemented manually. The development of both methods is presented for the anchorage design of windows subjected to blast loads. [ABSTRACT FROM AUTHOR]

This paper introduces a probabilistic assessment of steel column damage caused by blast loads, utilizing simulation reliability methods and gene expression programming. The research focuses on an H-section steel column and incorporates uncertainties associated with input loads (axial and blast loads) and geometric factors (i.e., maximum slenderness) under various boundary conditions (pinned and fixed supports). The reliability analysis employs three different methods: the point estimate method (PEM), the Monte Carlo simulation (MCS) method, and the Monte Carlo simulation with Latin hypercube sampling method (MCS-LHS). To perform the reliability analysis, formulas derived from a previous study conducted by the authors using gene expression programming (GEP) were employed. Damage assessment was carried out based on a damage index criterion, considering the post-blast residual axial load-bearing capacity of the steel column. The research results are presented in terms of damage probability, considering the different reliability analysis methods and boundary conditions. The findings demonstrate that the PEM effectively estimates the probabilistic response of the steel column with acceptable accuracy and less effort compared with the MCS and MCS-LHS. Furthermore, the MCS-LHS demonstrates higher accuracy in estimating the probability distribution function by utilizing the Latin hypercube sampling (LHS) method, as compared to the MCS. These findings emphasize the importance of considering uncertainties in calculating the column response under extreme dynamic blast loading. [ABSTRACT FROM AUTHOR]

Aiming at the problem that the blast load, generated by the explosion of the tandem-shaped-charge warhead, may cause damage to the warhead structure, material failure and even phase change, the material damage and structural protective capacity of the near-field blast load on the sandwich structure with foam-aluminum core were investigated by experimental test and numerical simulation. Firstly, the near-field blast test was performed to observe the deformation of sandwich structure and to collect the acceleration signals of fuze. Then, the mechanical properties of foam materials were tested, and a numerical model of blast load environment was established in the explicit dynamics software ANSYS/LS–DYNA 2020 R2. Finally, the experimental test data and simulation results were compared and analyzed. The strong agreement between the experiment and the simulation results indicates that the calculation method and simulation model are reasonable. Furthermore, the damage mode of foam-aluminum core materials with different densities and cell diameters under near-field blast load were carefully analyzed by simulation method. The simulation results show that, with the decrease of the density of foam-aluminum material and the increase of the cell chamber diameter, the deformation of the foam-aluminum panel gradually increases; the acceleration peak value of the fuze gradually decreases, and the pulse width barely changes and remains basically constant; the start and end times of the peak stress of the fuze cover gradually lag behind, and the peak stress hold-up time increases gradually; the maximum displacement deformation of the fuze cover decreases firstly and then increases. This work is expected to provide basic data and design guidelines for the graded foam sandwich panels of the blasting warhead fuze against the near-field blast load. [ABSTRACT FROM AUTHOR]

A number of recent studies have demonstrated numerically and experimentally that metaconcrete made of engineered aggregates can mitigate the propagation of stress waves induced by impulsive load. The energy imparted into the metaconcrete structure from impulsive load can be absorbed by engineered aggregates because of the local vibration of heavy cores. The previous studies considered simple 1D metaconcrete bar structure to investigate its effectiveness on mitigating stress wave propagations. The performance of structural components made of metaconcrete under impulsive load has not been investigated yet. In this study, 3D meso-scale models of three typical beams, namely, normal concrete (NC) beam, normal metaconcrete (NMC) beam composed of normal engineered aggregates (NEA) and enhanced metaconcrete (EMC) beam composed of enhanced engineered aggregates (EEA) are generated to investigate the responses of beam structure subjected to impulsive loading. The engineered aggregates NEA and EEA are designed via the software COMSOL to have the bandgaps coincident with the primary frequencies of stress wave generated in NC beam by the considered impulsive loads. Dynamic responses of three beams subjected to near-field blast loads with different scaled distances are studied via the software LS-DYNA. It is found that the EMC beam experiences less compressive and spalling damage than NC and NMC beams subjected to near-field explosion with the scaled distance of 0.15 m/kg 1 / 3 . Under blast loading from larger scaled distance explosions, the EMC beam experiences less severe flexural and flexural-shear damage than NC and NMC beams. It can be concluded that the EMC beam demonstrates better blast-resistance performance than NC and NMC beams. [ABSTRACT FROM AUTHOR]

The paper presents results of a research on robustness of sandwich panels subjected to the accidental load – impact blast wave. The accidental design situation is understood as an unexpected explosion of gas cylinders located in the neighbourhood of the building. Full‐size sandwich panels with lightly profiled, thin‐walled, steel facings and thick softcore were used in the experiments. The conducted field tests allowed for FE model validation in Abaqus/CEA environment. During the experiments, the two high‐speed cameras have been used to record the behavior of the sandwich panel. Furthermore, the failure mechanisms of the sandwich panels and fasteners were also revealed. The research outcomes are based on both field experiments and numerical simulations. [ABSTRACT FROM AUTHOR]

Due to good corrosion resistance and high tensile strength, glass fiber–reinforced plastic (GFRP) bolts are widely used in mining operations. However, GFRP bolts are susceptible to blast load damage, so it is important to understand their dynamic mechanical behavior. This experiment constructed a dynamic testing system to simulate the in situ rock bolt dynamic loading conditions. Using strain gauges, the axial load signals at different locations along the bolt were recorded and the corresponding axial stresses were analyzed. Moreover, a numerical model was established to analyze the axial stress distribution along the bolt under dynamic loading. The results showed that the maximum axial stress of GFRP bolt occurs at the bolt collar position and increases approximately linearly as the impact load increases. The axial stress decreased within a short distance from the bolt collar position following approximately an exponential function. In addition, the stronger the mechanical properties of the surrounding rock, the faster the axial stress decreases along the bolt and the greater the increasing rate of the maximum axial stress with an increase of the impact load. The location and increased characteristics of the maximum axial stress in metal and GFRP bolt were similar, but the dynamic load significantly affected the existence range and decreasing rate of axial stress in GFRP bolts than in metal bolts. [ABSTRACT FROM AUTHOR]

The safety of civilian and military infrastructure is a concern due to an increase in explosive risks, which has led to a demand for high-strength civil infrastructure with improved energy absorption capacity. In this study, a Finite Element (FE) numerical model was developed to determine the effect of hybrid Fibre Reinforced Polymer (FRP) as a strengthening material on full-scale Reinforced Concrete (RC) slabs. The reinforcing materials under consideration were Carbon (CFRP) and Glass (GFRP) fibres, which were subjected to blast loads to determine the structural response. A laminated composite fabric material model was utilized to model the failure of composite, which facilitates the consideration of strain rate effects. The damaged area of the laminate is determined in the FE model, and it is in good agreement with the corresponding experimental results in the literature. Models containing different stacking sequences were built to demonstrate their efficiency in resisting blast loads. In general, the damaged area was reduced when a hybrid reinforcement with CFRP as the top layer was used. [ABSTRACT FROM AUTHOR]

In this study, the characteristics of static bending and free and forced vibration of double-layer auxetic functionally graded porous (FGP) sandwich plates with shear connectors under blast load are explored comprehensively, where the structure of the plate comprises two layers joined by shear connectors. Each layer comprises auxetic FGM sandwich material, containing a core component made of auxetic honeycomb with a negative Poisson's ratio, while the upper and bottom two components are made from FGP materials. The whole plate is supported by a two-parameter Winkler-Pasternak elastic foundation. The key innovation of the proposed theory is that the transverse shear stresses are zero at the two free surfaces of each layer. In contrast to previous first-order shear deformation theories, no shear correction factor is required. To solve the plate issue when the boundary condition was entirely supported, Navier's exact solution was devised. On the other hand, in order to address the plate behavior in the event that the boundary condition was altered in any way, a plate element with nine nodes was used. Besides, to determine whether or not these results are accurate, a complete comparison approach that makes use of reliable claims has been used. The problem model's special case situations are used in order to accomplish this goal. When the object being developed is exposed to explosive loads, the findings that were derived from this research have the potential to be used to the construction of both military and civil works.

The explosion products, such as shock waves, fragments and heat energy formed by explosion, act on the plate structure, which may cause structural damage, material failure and even phase transformation of material. In this paper, the damage mechanism and protective effect of near-field blast load on sandwich structure based on foam-nickel core material were studied. Firstly, the near-field explosion test was conducted to investigate the blast response of the foam-nickel sandwich structure subjected to blast shock from 8701 explosive at near-field position. The deformation characteristics and stress history of the sandwich structure on the acting location of blast load were carefully investigated via experimental methods. A finite element model of near-field explosion was established for effective numerical modelling of the dynamic behaviour of the sandwich structure using the explicit dynamics software ANSYS/LS-DYNA for more comprehensive investigations of the blast shock response of the sandwich structure. The finite element model is reasonable and validated by mesh independence verification and comparing the simulated response behaviour to that from the experimental results for the sandwich structure subjected to near-field blast load. On this basis, the damage mechanism and protection effect of the near-field explosion impact on foam-nickel cores with different density and porosity are simulated more systematically. The investigated results from the experiments and a series of numerical simulations show the large deformation effect due to the extensive energy absorption, which suggests that the sandwich structure based on foam-nickel core material may be expected to become a new choice of protective structure under near-field blast load. [ABSTRACT FROM AUTHOR]