External Blast Loading Research Articles

Dynamic Response of Gradient Aluminum Foam Sandwich Tubes under External Explosive Loads.

In this paper, we numerically investigate the dynamic response and explosion resistance of gradient aluminum foam sandwich tubes subjected to external blast loads. Based on 3D-Voronoi technology, we construct density-graded aluminum foam cores to systematically explore the influence of core density distribution, density gradient, and average relative density on the protective performance of these structures. Our primary objective is to identify optimal design parameters that maximize explosion mitigation capabilities while balancing energy absorption and specific energy absorption capacities. The research results show that a positive gradient core configuration exhibits superior anti-explosion performance, significantly outperforming its uniform and negatively graded counterparts, particularly when the gradient value is substantial. For the positive gradient cores, an increase in the gradient value leads to a corresponding enhancement in explosion resistance. Conversely, in negatively graded cores, a higher gradient value diminishes the anti-explosion performance. Furthermore, while augmenting the relative density of the core layer does improve the overall explosion resistance of the sandwich tube, it comes at the cost of reduced energy absorption and specific energy absorption capabilities, highlighting the need for a delicate balance among these competing factors.

Experimental investigation on the deformation and damage of steel ribbon wound vessel for hydrogen storage under external impact and blast loading

Steel ribbon wound vessel is a preferred type for stationary storage of high-pressure hydrogen in refueling stations. However, it is under the threat of fragment impact and blast loads caused by accidental explosions of hydrogen or other vessels. For the first time, the fragment-simulating projectile (FSP) impact tests with impact kinetic energy range from 1.8 × 103 J–4.9 × 103 J and external blast loading tests with TNT equivalent range from 157 g–4 kg of industrial-grade 50 MPa steel ribbon wound vessel were carried out. The damage of vessel under FSP impact loading was studied. The effect of concentrated and distributed blast loads on the deformation and damage of gas-filled vessel was analyzed, and the explosion resistance of vessel under near-field blast loading was explored. It is revealed that: 1) the steel ribbon wound vessels generally have good resistances to external blast and impact loads, 2) the primary damage characteristics of vessel under contact/near-field blast loading was localized depression deformation, accompanied by steel ribbons warping as the shock wave impulse increases, 3) the saddle fails earlier than the vessel under the near-field blast loading. Further, the failure modes of vessel under extreme blast loads were revealed. Results can provide reference for the safe design and validation of dynamic damage/failure analysis models of steel ribbon wound vessels.

Dynamic response and vibration modes of multi-layer wound cylindrical shell for hydrogen storage under external blast loading

Multi-layer wound cylindrical shells are the preferred structures for storage vessels working in high pressure and hydrogen atmosphere. However, they are susceptible to external blast loads from accidental hydrogen explosions. In order to study the response of such structures under external blast loading, a numerical model was developed, which combined a thermo-viscoplastic constitutive model and a fluid-structure coupling approach, and was subjected to external blast loads of different TNT equivalency weights. The strain responses and initial velocity fields of the structure were analyzed. A rigid-plastic theoretical model was also developed to calculate the maximum displacement of the inner shell and was compared with the simulation results. Moreover, the axial velocity vibration histories and dominant frequencies at different locations of the steel belts were numerically obtained. In addition, four vibration modes of the steel belts were presented in this paper. Furthermore, strain growth was observed in the high-frequency vibration area, and the possible reasons for the strain growth were analyzed and discussed in detail. The results will be useful for predicting the deformation modes of such multi-layer wound cylindrical shell structures under the risk of external hydrogen explosions.

Deformation and Dynamic Response of Steel Belt Staggered Multilayer Cylindrical Shell Under External Blast Loading

Abstract The deformation and dynamic response of a multilayer cylindrical shell composed of an inner shell and fourteen outer layers under external blast loads of different trinitro-toluene equivalency weights were studied. A numerical model using the thermo-viscoplastic constitutive model and considering fluid–structure coupling between explosion wave and structure was developed. The displacement in axial direction and cross section, as well as the effective strain responses, were analyzed to demonstrate the potential deformation of the shell structure. Results demonstrate that different materials cause inconsistent displacement and separation to develop in the inner and outer shells. In order to address the problem that the displacement of the inner shell is hard to measure due to the shielding and covering of the outer shell, a theoretical formula for calculating the maximum displacement of the inner shell was developed. The deflection process and stress triaxiality histories of the inner shell were investigated, and the results showed that compressive stress is the primary cause of plastic deformation. Additionally, the delamination that appeared in the outer shell was discussed, and it was revealed that there are two factors of delamination: (1) Stress waves spread across adjacent layers in the opposite direction because steel belts were wound in the opposite direction between the two adjacent layers; (2) Outer layers experienced uneven compressive loads. The results will be helpful to provide a reference for the intrinsic safety design of such multilayer cylindrical structures for hydrogen storage, etc.

A Numerical Study of Blast Resistance of Carbon Fiber Reinforced Aluminum Alloy Laminates

In this study, the dynamic responses under blast loading of carbon fiber reinforced aluminum alloy laminates with different curvature radii, different numbers of layers, and different layer directions of carbon fiber under blast loading were compared numerically. The finite element models were built with ABAQUS/Explicit. To calibrate the numerical models, experiments on curved carbon fiber and curved aluminum alloy were modeled, and the numerical results showed good agreement with the experimental data. The calibrated numerical models were used to simulate the dynamic response of cylindrical panels subject to external explosion loading. The stiffness degradation coefficient was introduced to more accurately simulate the failure mode of the composite structures. The deformation and energy absorption of carbon fiber reinforced aluminum alloy laminates under different structural parameters were obtained. These simulation findings can guide the theoretical study and optimal design of carbon fiber reinforced structures subject to external blast loading.

Simulating the response of buried structures to external blast loads: Methods, challenges, and advances

AbstractVarious methods have been proposed to ensure the serviceability of buried structures such as road tunnels, urban utility tunnels, water conduits, underground shelters, and deposition chambers against extreme loads, the most common of which are experimental and computational methods. An external explosion in the vicinity of such structures is one of these extreme loads. In general, different types of external blasting for buried structures can be classified as surface blasting, coupled or uncoupled buried explosions, excavation by drilling and blasting near the structure, and the accidental detonation of explosive depositions. Laboratory or field tests for explosions are usually limited by financial and safety constraints; therefore, numerical simulations are often regarded as a vital tool in the study of such problems. Though computer software and hardware have improved rapidly in recent decades, and various numerical solvers have been developed, there is no universal method for solving all external explosion problems. Each numerical method can produce sensible results under certain conditions and assumptions, along with its limitations in computational cost. Consequently, these problems have been particularly difficult to investigate, and even in some cases, the results of different studies seem to be inconsistent. Besides providing an extensive review of the available literature in the field of numerical simulation of external explosions near buried structures and a discussion of the damage criteria associated with such explosions, this study also highlights some inconsistencies that may need further investigation.

Experimental and numerical study of damage mechanism of steel box girders under external blast loads

Steel box girders are commonly utilized in bridge construction, particularly in continuous bridges and long span cable-stayed and suspension bridge. The bridges are vulnerable to blast loads induced by accidental explosions and terrorist attacks. Moreover, these types of explosions always occur above the bridge decks. Hence, the steel box girders subjected to blast loads were investigated in this study. A field blast experiment on a steel box girder was carried out. Furthermore, a finite element model (FEM) was developed and validated by the experimental results. And the FEM yielded the same results as the experiment. The damage mechanism of the experimental specimen was revealed by the numerical model. The results showed that the damage of the steel box girder concentrated on the top plate, and the experimental specimen can be simplified to the analysis of stiffened plate. Based on the validated finite element model, parametric analysis was performed. The maximum displacement responses of the top plate, the damage modes and mechanisms, and the energy dissipation mechanism were discussed. The blast load parameters and the transverse web thickness were all found to have significant influences on the displacement responses of the top plate. Three main damage modes were observed in the steel box girder subjected to blast loads. The transverse web thickness has a substantial impact on the damage modes. Moreover, the damage mechanisms of the damage modes were revealed. When considerable plastic damage occurs, most of the energy is absorbed by the top plate and transverse web components, according to an examination of the energy absorption mechanism. The strength of the blast loads and the transverse web thickness significantly influence the energy absorption ratio of the top plate and transverse web components. The types of damaged components should be reduced from the standpoint of repairability. Hence, through the analysis, it is advised to increase the transverse web thickness to improve the repairability of the steel box girder after explosions.

External blast flow field evolution and response mechanism of single-layer reticulated dome structure

Single-layer reticulated dome structure are commonly high-profile building in the public and can be attractive targets for terrorist bombings, so the public can benefit from enhanced safety with a stronger understanding of the behavior of single-layer reticulated dome structure under explosion. This paper investigates the fluid-structure interaction process and the dynamic response performance of the single-layer reticulated dome under external blast load. Both experimental and numerical results shown that structural deformation is remarkably delayed compared with the velocity of blast wave, which advises the dynamic response of large-span reticulated dome structure has a negligible effect on the blast wave propagation under explosion. Four failure modes are identified by comparing the plastic development of each ring and the residual spatial geometric of the structure, i.e., minor vibration, local depression, severe damage, and overall collapse. The plastic deformation energy and the displacement potential energy of the structure are the main consumers of the blast energy. In addition, the stress performance of the vertex member and the deep plastic ratio of the whole structure can serve as qualitative indicators to distinguish different failure modes.

Sensitivity analysis and probability modelling of the structural response of a single-layer reticulated dome subjected to an external blast loading

The structural response of a single-layer reticulated dome to external explosions is shaped by many variables, and the associated uncertainties imply non-deterministic results. Existing deterministic methods for predicting the consequences of specific explosions do not account for these uncertainties. Therefore, the impact of the uncertainties associated with these input variables on the structures’ response needs to be studied and quantified. In this study, a parametric uncertainty analysis was conducted first. Then, local and global sensitivity analyses were carried out to identify the drivers of the structural dynamic response. A probabilistic structural response model was established based on sensitive variables and a reasonable sample size. Furthermore, some deterministic empirical methods for explosion-resistance design, including the plane blast load model of CONWEP, the curved blast load model under the 50% assurance level, and the 20% mass-increased method, were used for evaluating their reliability. The results of the analyses revealed that the structural response of a single-layer reticulated dome to an external blast loading is lognormally distributed. Evidently, the MB0.5 method based on the curved reflector load model yielded results with a relatively stable assurance rate and reliability, but CONWEP did not; thus, the 1.2MB0.5 method can be used for making high-confidence simple predictions. In addition, the results indicated that the structural response is very sensitive to the explosion parameters. Based on these results, it is suggested that for explosion proofing, setting up a defensive barrier is more effective than structural strengthening.

Evaluation of masonry walls subjected to blast loading based on material modelling approach

Historical buildings subjected to extreme loading cases such as earthquake or external blast loading become the most attractive from the researcher's point of view. This is mainly due to increasing accidental and intentional explosion events around the world. As most of the historical buildings, mainly are masonry structures, were not designed and constructed against such extreme loading events, the structural blast assessment is a matter of consideration among engineers and researchers. In this paper, different material models available in the literature, e.g., Homogenization Techniques, have been discussed to further understand their applications in numerical simulation approaches. Since the Homogenization Techniques lack the ability to model different failure patterns of bricks and mortars, the efficient and inexpensive material model, detailed micro modelling, is selected to simulate masonry walls numerically. The influence of boundary conditions on the blast behaviour of the masonry walls is also investigated. The result of the numerical simulation shows that the selected material models and boundary conditions have a substantial impact on the masonry wall’s responses under blast loading. In addition, the induced blast over pressure interaction on the masonry structure wall has been compared with numerical and experimental results in the literature. It is concluded that the proposed anatomy-based representative volume element provides a better understanding of the material microstructure and its corresponding effective stiffness properties in the longitudinal and lateral directions.

External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial, residential, and military infrastructure. Therefore, it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations. This paper investigates the effect of blast load variability on the design value and the structural dynamic response. Therefore, the sources of uncertainty in the external blast load on dome structures were discussed firstly. Then based on the probabilistic blast load model for the dome, the rationality of a deterministic mass-increase safety method was assessed. It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof. In addition, it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method. A sensitivity analysis on the probabilistic blast load was conducted, and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load. Therefore, based on the Latin hypercube sampling method, a reliability-based external blast load factor technique was proposed. This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements, associated with a low, medium, and high level of protection grades for a specific explosion scenario, and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity. This study herein can serve as a reference for the calculation method of designed blast load.

Review of the estimation methods for external blast loads on structures

A review of external blast loads on structures modeling methods is presented in the paper. Also, numerical simulations of explosions in an urban scenario were done in software Ansys AUTODYN, and compared to experimental data. Recommendations were given regarding the use of numerical simulations in blast wave parameter calculations for the urban environment, as well as suggestions for further research.

Numerical and analytical study of overpressures and impulses inside a masonry box subjected to external blast loading

Blast loads have attracted considerable attention in recent years due to accidental or intentional events involving important structures, which have occurred around the world. The activities related to terrorist attacks have increased and, unfortunately, the current trend suggests that they will continue to rise in the future. In relation to the design of structures subjected to blast loadings, there are still many uncertainties in the specialized technical literature. Particularly, the overpressures and impulses inside constructions are difficult to estimate due to many reflections of the shock wave. The main objective of this work is to study the propagation of the blast wave inside constructions subjected to external loadings. An experimental study was performed using a masonry box with reinforced concrete beams and columns and a typical window. The results were previously presented. In this article, numerical models are developed in order to compare results and to obtain design guidelines. Explosive charges of equivalent 1–5 kg of TNT and elevated 1 m above the ground were detonated at different distances from the window, and overpressures and impulses were obtained at five points inside and outside the room. However, empirical–analytical results using a well-known technical manual are also obtained and compared. The obtained results are useful to evaluate numerical codes and empirical formulas.

A comparative study of blast resistance of cylindrical sandwich panels with aluminum foam and auxetic honeycomb cores

The dynamic response of cylindrical sandwich panels with aluminum foam core, hexagonal honeycomb core, and auxetic honeycomb core are compared numerically. A novel curved auxetic honeycomb core is designed, and the finite element models are built by employing ABAQUS–Explicit. To calibrate the numerical models, the experiments of sandwich panels with honeycomb core and aluminum foam cores are modeled. And the numerical results have a good agreement with the experiment date. The calibrated numerical models are used to simulate the dynamic response of cylindrical panels subject to external blast loadings. It is found that the cylindrical panels with auxetic honeycomb cores have a better performance than that with aluminum foam cores and hexagonal honeycomb cores in resisting blast loadings. A material concentration effect was observed in the auxetic honeycomb core due to the negative Poisson's ratio (NPR) effect. According to parameter studies, it is concluded that with the increase of curvature and face sheet thickness the blast-resistance of panels with both auxetic honeycomb core, hexagonal honeycomb core, and foam cores increased obviously, especially the panels with auxetic honeycomb cores. For the panels with auxetic honeycomb cores, increasing the back face sheet thickness can improve the blast-resistance performance more efficiently than increasing the thickness of front face sheet, which is opposite for the panels with foam cores and hexagonal honeycomb cores. Auxetic cores with a smaller unit cell aspect ratio and a smaller unit cell length ratio has a larger Poisson's ratio, and achieves better blast resistance performance. These simulation findings can guide well the theoretical study and optimal design of cylindrical sandwich structures subject to external blast loading.

Experimental and numerical investigations of a single-layer reticulated dome subjected to external blast loading

Long-span spatial structures are commonly used as landmarks in modern cities and may be potential targets of terrorist attacks; thus, it is important to study the dynamic behaviour of such structures under blast actions. In this study, experiments were conducted on two reduced-scale models which were designed and manufactured. The aims of the experiments were to (i) assess the accuracy of a numerical approach for simulating the structural dynamic responses based on the finite element software, “ANSYS/LS-DYNA”, and (ii) survey the various failure modes of single-layer reticulated domes under an external blast loading. The numerical results showed a good agreement with the experiments when the empirical load model was used to study the elastic and inelastic deformation of a multi-curved shell. Additionally, the deformation, development of plasticity, and energy absorbing behaviour of each component were examined, and the following four major response patterns were identified: elastic vibration, slight damage, local failure, and global collapse.

Total Energy of Hemi-cylindrical Shells Subjected to Blast Loading: Comparison with Theoretical Method

This study presents the total energy response of the hemi-cylindrical shell with a steel material under the external blast loading by employing both theoretical approach and numerical simulation. Analytical approach demonstrate that the total energy contributed from blast is inverse proportional to the thickness of shell. It is proportional to the inverse tangent function applied by the ratio of denotation coordinate over the radius of shell. Moreover, to verify the theoretical inference, several numerical simulations were carried out. Those result agree well.

Dynamic response of single-layer reticulated shell with explosion-protection wall under blast loading

To investigate the structural dynamic response of long span reticulated shell under external blast loading considering explosion-protection wall, explicit finite element (FE) programme LS-DYNA is used to set up the analytical model of explosion-protection wall corresponding to an experiment to grasp the propagation law of blast shock waves around the wall. The results of simulation and experiment are compared and the results verify the creditability and applicability of numerical simulation by using ALE (Arbitrary-Lagrange-Euler) algorithm. A Kiewitt8 single-layer reticulated shell of refinement with span of 40 m is established to simulate the responses of structure considering explosion-protection wall, which contains reticulated shell member, purlin hanger, purlin, rivet and roof boarding. According to simulation results from the maximum nodal displacement, average plastic strain and yielding degree of cross section of reticulated shell member, the dynamic response laws are proposed based on varying parameters, including height, position, length, material of the explosion-protection wall, rise-span ratio of reticulated shell and TNT explosive weights. Meanwhile, the influence rules of explosion-protection wall and structure on diffraction and reflection action of blast shock wave are obtained. In addition, the adverse height of the explosion-protection wall for reticulated shell with span of 40 m under external blast loading is proposed. Four damage types of reticulated shell with the explosion-protection wall subject to external blast loading are defined by summarizing all the structural response of FE numerical models, which could provide reference for reasonable explosion-proof design for reticulated shell structure.

Modelling the Slab Failure of an Open Structure Acted by External Blast Loads

Abstract The explosion of bombs near buildings generally yields severe damages to the structures. Explosion resistant standards and requirements are constantly being developed and upgraded. This paper focuses on the damages which occur toa RC slab due to blast action. The numerical model replicates a ¼ scale experiment. The analysis is conducted using a software based on the recently developed Applied Element Method. This numerical method is able to model accurately all the structural behavior stages up to failure. The results are compared to experimental data available in the literature. The analysis reveals that the slab failure due to uplift pressures may be avoided by some simple reinforcing details, as they are listed in the Romanian National Annex – accidental loads of the Eurocode EN 1991-1-7.

Simplified damage assessment of slab against external blast load

Recently, the mode approximation method (MAM) has been adopted to analyze beam elements against blast load. However, in real cases, the main structural element of an underground structure is slab and side wall since they not only support the structure itself but also may sustain external loads from blast, earthquake, and other kinds of impact. In the present study, the MAM is extended from beam to plate elements and the soil-structure interaction is considered and simplified when calculating structural response under blast load. Pressure-impulse diagrams are generated accordingly for further quick damage assessment.

Structural Response under Blast Loads - Simplified Numerical Analysis

Efficiently and accurately predicting structural dynamic response and damage to external blast loading is a big challenge to both structural engineers and researchers. Theoretical investigation on this problem is complex as it involves non-linear inelastic material properties, effect of time varying strain rates, uncertainties of blast load calculations and the time-dependent structural deformations. Experimental investigation can provide valuable data for locating the damage and establishing the damage criteria. The damage curves generated from the extensive experimental study can provide quick assessment of the structural status. However, such blast experiments always involve safety concern and can be beyond the affordability. Besides this, the correlation of the experimental data with predictive method is difficult since it requires a large number of tests to generate damage curves. Compared with the theoretical and experimental study, numerical simulation does not involve any safety concern and is cost-effective. With verified material model and element model, numerical simulation could be powerful supplement to the experimental tests. However, numerical simulation of structural responses under blast and impact loading could be time and resource consuming. Even with modern computer technology and computational mechanics method, detailed modelling and numerical simulation of responses of structures subjected to blast loadings are still often prohibitive. To address this issue, in the present study, an efficient numerical method is proposed to reliably calculate structural response and damage to blast loadings.