Close-in Blast Research Articles

Prediction and analysis of damage to RC columns under close-in blast loads based on machine learning and Monte Carlo method

Rapid prediction and quantitative assessment of the damage of reinforced concrete (RC) columns under blast loads are challenging and crucial issues. The key parameters affecting the anti-blast capacity of RC columns are coupled with failure modes. In this study, machine learning (ML) and Monte Carlo (MC) simulations are employed to investigate the damage of RC columns subjected to blast loads. 257 data collected from existing experimental and numerical studies are utilized to establish a database for model training and testing. The damage indexes of columns are predicted using eight ML models with eight input features. The predictive capacity of each model is characterized by eight evaluation indexes through MC simulations. The CatBoost model is identified as the optimal model based on the Analytic Hierarchy Process (AHP). Additionally, the CatBoost model is explained using the SHapley Additive exPlanations (SHAP) method, and the influence of axial compression ratio on column damage is determined to be intricate. The coupling relationship between the axial compression ratio and the scale distance of the column is analyzed. Finally, a zonal diagram is developed. This diagram can be utilized to assess the damage of the RC column quickly and efficiently.

Characterization of combined blast- and fragments-induced synergetic damage in polyurea coated liquid-filled container

Liquid-filled containers (LFC) are widely used to store and transport petroleum, chemical reagents, and other resources. As an important target of military strikes and terrorist bombings, LFC are vulnerable to blast waves and fragments. To explore the protective effect of polyurea elastomer on LFC, the damage characteristics of polyurea coated liquid-filled container (PLFC) under the combined loading of blast shock wave and fragments were studied experimentally. The microstructure of the polyurea layer was observed by scanning electron microscopy, and the fracture and self-healing phenomena were analyzed. The simulation approach was used to explain the combined blast- and fragments-induced on the PLFC in detail. Finally, the effects of shock wave and fragment alone and in combination on the damage of PLFC were comprehensively compared. Results showed that the polyurea reduces the perforation rate of the fragment to the LFC, and the self-healing phenomenon could also reduce the liquid loss rate inside the container. The polyurea reduces the degree of depression in the center of the LFC, resulting in a decrease in the distance between adjacent fragments penetrating the LFC, and an increase in the probability of transfixion and fracture between holes. Under the close-in blast, the detonation shock wave reached the LFC before the fragment. Polyurea does not all have an enhanced effect on the protection of LFC. The presence of internal water enhances the anti-blast performance of the container, and the hydrodynamic ram (HRAM) formed by the fragment impacting the water aggravated the plastic deformation of the container. The combined action has an enhancement effect on the deformation of the LFC. The depth of the container depression was 27% higher than that of the blast shock wave alone; thus, it cannot be simply summarized as linear superposition.

Advancing blast fragmentation simulation of RC slabs: A graph neural network approach

Accurate prediction of blast-induced fragmentation in reinforced concrete (RC) structures is pivotal for structural debris hazard assessment in an explosion event. This assessment is essential for designing effective measures for protection of people and structure in the vicinity. While conventional computational techniques are proficient, they are computationally very demanding and may not be readily adaptable in practical applications. This study proposes a novel approach, the Fragment Graph Network (FGN), a specialized variant of graph neural networks (GNNs), to simulate complex interactions between macro-level particles of RC structures subjected to close-in blast loads. The RC structure is discretised into particles, with the model predicting structural responses and fragmentation based on states of these particles. Utilizing an autoregressive prediction mechanism, our model can accurately simulate spatiotemporal responses of RC slabs against blast loads. The efficacy of the model was tested on a dataset consisting of 149 simulated cases, encompassing around 180,000 states each, covering a wide range of blasting scenarios and structural design parameters including TNT charge weight, standoff distance, slab dimension, concrete strength, and reinforcement ratio and layout. Notably, the proposed model delivered accurate predictions, achieving relative errors under 10% and R2 values exceeding 0.93 for both standard and extrapolated test scenarios as compared to the SPH simulations. Remarkably, our model dramatically outpaced traditional numerical approaches, reducing simulation times from hours to minutes on CPUs and seconds on GPUs. This pioneering effort paves the way for efficient and accurate simulations of RC blast fragmentations, offering a rapid alternative to standard numerical approaches.

Close-in blast performance of RC beams with varying cross-sectional sizes and damage assessment based on the dynamic load carrying capacity

Aiming to investigate the impact of cross-sectional size on the close-in blast performance of reinforced concrete (RC) beams, the local damage features and structural responses of RC beams with varying cross-sectional widths and depths subjected to close-in explosions were investigated experimentally and numerically. Experiments were conducted on ten RC beams with a cross-sectional size of 25 cm × 12.5 cm to study the influence of scaled distance and charge mass on the local damage size and structural responses (displacement and reaction force). The results indicate that the blasting face damage to tested beams, such as the crushing crater of concrete cover and side peeling-off damage, is more sensitive to the scaled distance (intensity of applied blast loads) compared to the rear spalling damage. And the peak reaction force exhibited a gradual increase within the range of 0.5 m/kg1/3, eventually reaching an average maximum value of 93.5 kN, and remained unchanged after the scaled distance was greater than 0.5 m/kg1/3, indicating that the dynamic load-carrying capacity of tested beams increased with the increasing scaled distance and the maximum dynamic load-carrying capacity of these beams is around 93.5 kN. Furthermore, a numerical model of RC beams subjected to close-in explosions was established based on the Fluid-Structure-Interaction (FSI) method. For validation, the local damage morphology and sizes of RC beams and their dynamic responses (displacement and reaction force) were computed and compared with the corresponding experimental results, concluding that the numerical results are in good agreement with the experimental findings. A parametric analysis was conducted to study the impact of cross-sectional size on the development process of initial local damage, stress distribution in cross sections, local damage sizes, and structural responses. Moreover, a damage index of the dynamic load-carrying capacity was derived from the relationship between the normalized maximum reaction force and the normalized maximum displacement to assess the damage degree of RC beams with varying cross-sectional sizes. This work can serve as a partial reference for relevant research.

Prediction of direct shear failure in blast-loaded reinforced concrete members

The occurrence of direct shear failure in structural members during the early phases of blast loading prior to the development of appreciable curvature can lead to sudden and catastrophic consequences for protected facilities exposed to near-field and/or close-in blasts. Thus, accurately predicting direct shear failure in structural members subjected to blast loads is crucial. Consequently, this paper presents a novel 3-D finite element (FE)-based cohesive interface modeling approach capable of capturing the shear slip near the supports and accurately predicting direct shear failure in blast-loaded reinforced concrete (RC) members. The validity of the proposed numerical model is established with experimental data. Three distinct blast load cases varying from distant to close-in are applied to verify the applicability and highlight the novelty of the proposed model. Results show that direct shear failure is inherently captured within the modeling framework of the proposed cohesive interface models, eliminating the need for externally adopted damage criteria seen in existing 3-D FE-based continuum models. Further, the effectiveness of the cohesive interface model in the accurate blast damage assessment of structural members is manifested by using pressure-impulse (P-I) diagrams.

Close-in blast responses of bowstring fold-line-core sandwich panels

Buildings, critical facilities, and military transport must maintain structural integrity when subjected to explosions. This research introduces a novel protective structure employing a bowstring design and curved sandwich panels featuring a fold-line-core designed to improve the explosion resistance of thin-walled panels. The dynamic responses and crushing modes of these bowstring fold-line-core sandwich panels were examined. The findings demonstrate that the bowstring fold-line-core sandwich panel effectively harnesses the self-supporting capacity of the bowstring structure alongside the energy absorption capabilities of the fold-line-core, resulting in exceptional anti-explosion performance. When subjected to a detonation of 200 g of TNT at a stand-off distance of 0.6 m, the designed panels exhibit minimal deformation. Moreover, the calculated proportional stand-off distance under corresponding operating conditions amounts to 1.026 kg/m1/3.

Numerical and Experimental Investigation on Aluminium 6061 Solid Cylindrical Bar Subjected to Close-in Blast Loading

Compaction force generated by blasting load requires strong material such as steel to act as a plunger to spread the force evenly. The problem with this method is retaining the plunger's original dimension from intolerable deformation. This paper uses ABAQUS software to study the ability to predict the response of solid cylindrical aluminium bars (6061) subjected to different close-in blast loads. The solid cylindrical aluminium bars treated as a plunger were evaluated numerically using a combination of the finite element method (FEM) and smoothed particle hydrodynamic (SPH) methods. The plunger was simulated using the Johnson-Cook (J.C.) model, and Jones-Wilkins-Lee (JWL) equation parameters modelled the explosive. Field tests were conducted by detonating explosives of two different weights, which are 100g and 250g, in the designated blast area. Both data and observation were compared and analysed regarding deformation behaviour in term of dimension difference and fracture. Based on the graph of the deformation dimension versus the plunger length, the deformation trend shows a very close relation between numerical and experimental data with a percentage error of less than 4%. The fracture mode generated using FEM is comparable to the actual specimen. This fracture mode can be described as similar to the behaviour of the specimen obtained using the Taylor impact test. Thus, it can be concluded that the numerical analysis performed for this study is consistent with the actual results.

Failure assessment of concrete shear walls under close-in blast based on viscous damage model

In this research, failure of reinforced concrete shear walls under close-in blast is evaluated based on numerical analysis. By introducing the Duvaut–Lions type damage driving stress rate, a dynamic viscous damage evolution law for concrete materials is constructed under the framework of elastoplastic damage theory. The rate effect-induced increase in concrete strength is well captured by the suggested model. For validation, the response of reinforced concrete slabs in blast tests and their mechanical behaviors after explosion were calculated, and the results are in good agreement with the experimental findings. Under blast loads at various scaled distances, the failure of a series of reinforced concrete shear walls with different axial load ratios is simulated, and the post-blast residual bearing capacity is calculated using a three-step loading analysis process. The ratio of the residual axial strength is defined to assess the performance degradation of the shear walls after blast, and the effect of different factors on the failure of structures under blast is examined.

Experimental and numerical analyses of the effect of fibre content on the close-in blast performance of a UHPFRC beam

Limited research has been conducted on the influences of fiber content on close-in blasting characteristics for ultrahigh-performance fiber-reinforced concrete (UHPFRC) beams. This paper aims to address this knowledge gap through experimental and mesoscale numerical methods. Experiments were conducted on ten UHPFRC beams built with varying steel fiber volumetric fractions subjected to close-in explosive conditions. Additionally, this study considered other parameters, such as the longitudinal reinforcement type and ratio. In the case of UHPFRC beams featuring normal-strength longitudinal reinforcement of diameters Φ12, Φ16, and Φ20, a reduction in maximum displacement by magnitudes of 19.6%, 19.5%, and 17.4% was observed, respectively, as the volumetric fractions of fiber increased from 1.0% to 2.5%. In addition, increasing the longitudinal reinforcement ratio and using high-strength steel longitudinal reinforcement both significantly reduced the deformation characteristics and increase the blasting resistances of UHPFRC beams. However, the effects on the local crushing and spalling damage were not significant. A mesoscale finite element model, which considers the impacts of fiber parameters on UHPFRC beam behaviors, was also established and well correlated with the test findings. Nevertheless, parametric analyses were further conducted to examine the impacts of the steel fiber content and length and the hybrid effects of various types of microfibers and steel fibers on the blasting performance of UHPFRC beams.

Effect of masonry infill on the response of reinforced concrete frames subject to in-plane blast loading

This paper presents a numerical study investigating the effect of masonry infill on the response of reinforced concrete (RC) frames subject to in-plane blast loading. Three-dimensional single-bay single-story masonry infilled reinforced concrete (MIRC) frames were modeled, in which a simplified micro-modeling approach was adopted for the masonry infill. The surface-based cohesive model was employed between the expanded brick units by adopting the traction-separation law. A non-integral modeling approach was considered with an appropriate contact algorithm between the infill wall and bounding RC frame. The dynamic material models with explicit dependency on strain rate were incorporated in the finite element (FE) models and validated against the experimental test data. The developed FE models of bare RC and MIRC frames were subjected to surface blasts with variable scaled distances representing the far-field, near-field, and close-in blasts. The effect of masonry infill on the response of RC frames subject to in-plane blast loading was investigated using the general-purpose FE software ABAQUS without employing user-defined subroutines. The blast response was characterized using displacements, energy dissipation, strain localization and accumulation, stiffness degradation, and damage modes. Results highlight the beneficial influence of masonry infill in reducing the local deformation and altering the failure modes of RC frames subject to in-plane blasts. However, results suggest that the effects of infill on the overall structural response, including axial, flexural, and shear demands, must be considered during the design of bounding RC frames. Furthermore, parametric studies were carried out based on varying masonry bonding patterns and wall thickness, number of bays and stories, and masonry infill heights, and provided conclusive remarks.

Full-Scale Field Tests on Concrete Slabs Subjected to Close-In Blast Loads

This research evaluates the performance of different protective solutions for reinforced concrete slabs subjected to blast loading. A series of full-scale blast tests were carried out on concrete slabs at scaled distances ranging from 0.20 to 0.83 m/kg1/3. For this purpose, 16 concrete slabs were tested; eight of them were unreinforced as ‘control specimens’, and the other eight were protected with five different protective solutions. After the tests, a damage assessment was conducted based on three different parameters. The results showed that there was no clear improvement in the concrete performance when the charge was located 0.5 m from the slab. Significant local damage that completely perforated the slab occurred. In the tests with the load placed 1 m from the slab, the reinforcements that were used significantly contributed to the retention of some fragments produced in these tests.

A review on close-in blast performance of RC bridge columns

A review on close-in blast performance of RC bridge columns

Multi-Hazard-Resistant Behavior of CFRP- and Polyurea-Retrofitted Reinforced Concrete Two-Column Piers under Combined Collision-Blast Loading.

This study investigated the multi-hazard resistance of highway bridge piers retrofitted with carbon-fiber-reinforced polymer (CFRP) and polyurea coating against the combined collision-blast loads and evaluated their effectiveness. Detailed finite element models of CFRP- and polyurea-retrofitted dual-column piers that considered the blast-wave-structure interactions and the soil pile dynamics were developed using LS-DYNA to simulate the combined effects of a medium-size truck collision and close-in blast. Numerical simulations were conducted to examine the dynamic response of bare and retrofitted piers under different levels of demands. The numerical results indicated that using CFRP wrapping or polyurea coating effectively mitigated the combined collision and blast effects and increased the pier's resistance. Parametric studies were performed to identify an in situ retrofit scheme to control the parameters and determine the optimal schemes for the dual-column piers. For the parameters that were studied, the results showed that retrofitting at half the height of both columns at the base was identified as an optimal scheme to improve the multi-hazard resistance of the bridge pier.

Experimental and Numerical Studies on Dynamic Response of Parallel Wire Cables Subjected to Close-In Explosions

The recent trend of increasing global terrorist attacks and identified vulnerabilities associated with critical bridges highlights the necessity to protect cable-stayed bridges from terrorist assaults. The cables are the most crucial load-carrying components within the envelope of a cable-stayed bridge, whose failure could result in the progressive collapse of the whole bridge structure with disastrous consequences. However, there is a very limited understanding of the blast effects on cables. This paper presents an experimental and numerical investigation of the blast performance of parallel wire cables under close-in explosions. Field blast tests were conducted on three identical parallel wire cable specimens with varying explosive charge weights. An equivalent beam–shell model was developed in LS-DYNA to reproduce the dynamic response of parallel wire cables subjected to close-in explosions and was comprehensively validated against the experimental results. With the validated numerical modeling techniques, the dynamic behavior of parallel wire cables in a realistic blast scenario of vehicle-borne improvise explosive devices (VBIEDs) detonated on the bridge deck was investigated. The results showed that high bending stress was induced in the cable end near the deck, indicating that the cable-to-girder anchorage zone is the most vulnerable position under the close-in blast scenario. Parametric analyses were carried out to further investigate the effects of cable dimension, prestressing force, cable length, and anchorage angle on the dynamic response of the parallel wire cables. It was found that the cables with smaller dimensions and higher prestressing force are more vulnerable, while the cable length and anchorage angle have limited effects on the performance. The results could be used in the safety evaluation and preliminary protective design of cable-stayed bridges under potential blast threats.

The Influence of Adiabatic Heat and Combined Blast Load and Fire Loading on the Response of Mild Steel Plates

This paper study the influence of adiabatic heat and fire loading on the behaviour of unstiffened mild steel plates subjected to close-in blast loads using finite element (FE) analysis. A quarter-symmetry 3D FE model consists of the steel plate, clamps and bolts was developed using Abaqus/CAE. Classical plasticity model was used as the material model in the steel plate and bolts. The clamps were assumed as an elastic material. Temperature-material properties relationship according to Eurocode 3 and Masui model was assigned to the steel plate. Conwep function was used to simulate the blast loads. The influence of strain rates was considered in the steel plate using the Cowper-Symonds equation. The FE model of the unstiffened plates was verified and validated against experimental data from literature, where a good agreement was achieved. The results suggest the adiabatic heat in the steel plates does not significantly influence the behaviour of the steel plates in both temperature-material properties models. The study then investigated the effect of combined blast loads and fire loading on the response of steel plates. The fire loading was applied by increasing the temperature in the steel from 200 °C to 1000 °C. Excessive deformation and thinning of the plate at the central area of the plate was observed. The thinning at the central area is pronounce than the thinning of the plate at the boundary between the clamp and the steel plate. Hence, the FE analysis suggests that the failure might occur at the central area of the plate, which could suggest a tearing type of failure. This type of failure is common in plates subjected to close-in blast loads. Therefore, this study has shown that the effect of adiabatic heat is insignificant, and the combined blast-fire loading might cause a similar type of failure as in plates subjected to blast loads only.

Mitigation of the blast load on RC column by hanging granite slabs

Reinforced concrete (RC) column, which is the critical axial load carrying structural component, is vulnerable to blast loads, especially to close-in blast loads. The blast damage of the RC column might lead to the progressive collapse of the whole building structure. Therefore, it is necessary to ensure that the RC column could survive under design blast loads once the building structure is at the risk of terrorist or accidental explosions. One of the solutions is that the RC column is designed to be strong enough to resist the blast loads, which is very expensive. While the other method is to protect the RC column against blast loads with energy absorb materials. The granite slab, which is often used as the decoration hanging outside the structural components, is utilized to mitigate the blast loads applied on the RC column. In this study, firstly the concept of hanging granite slab for mitigating blast load on RC columns is proposed. Furthermore, the finite element (FE) model for simulation of the blast wave interaction with the dry-hanging granite slab is established to reveal the protection mechanism of RC column hanging with granite slab based on the platform LS-DYNA. The accuracy of FE model is validated by comparing the numerical results and the test results from blast field test. The influences of slab thickness T and hanging distance D on blast mitigation are investigated. Finally, the blast load mitigation factors are proposed and their empirical model are established as a function of scaled distance Z, hanging slab thickness T and hanging standoff distance D.

Blast performance enhancement prediction of circular column with helical mesh reinforcement and strengthened with UHPFRC plaster, and CFRP wrapping under close-in blast

Blast performance enhancement prediction of circular column with helical mesh reinforcement and strengthened with UHPFRC plaster, and CFRP wrapping under close-in blast

Numerical investigation of Reinforced-concrete beam-column joints under contact and close-in blast application

The behavior of the concrete and the steel material under blast loads are different. They have different mode of failures under blast loads. Also, responses differ according to the blast types concerning the proximity of the charge kept. It causes different failure modes in the structural members. Close-in or contact blast causes the spallation of concrete. In the near-field blasts, it causes bending failure in the structural members. The behavior of the mode of failure of various joint types subjected to contact-blast and close-in blast loads are numerically studied here. Three different joints simulated to carry on blast loads—exterior beam-column joint, interior beam-column joint, and knee joint simulated numerically under the close-in and contact loads. The charge for the contact blasts were applied to the joint is placed in contact with the joint core, and was not put at the beam or the column member of the joint cut section. In the current work, the failure behavior and the response of the RC beam-column joints is concluded.

Residual axial capacity of concrete-filled double-skin steel tube columns under close-in blast loading

Concrete-filled double-skin steel tubes (CFDSTs) are comprised of two concentrically placed steel tubes with the annulus between the tubes filled with concrete. A number of researches have established the prospect of CFDST columns as ideal alternatives for conventional reinforced concrete (RC) columns subjected to extreme events such as earthquakes, fires and vehicular collisions. Since structural columns are the most critical axial load-bearing members in structures, after experiencing blast loading the residual axial strength of key columns is crucial in preventing catastrophic damage of structural systems. Current knowledge on the residual axial load-bearing performance of CFDST columns is very limited. This paper studies the post-blast performance of CFDST columns after subjected close-in explosions, where the residual axial load-bearing capacity of blast-damaged columns is quantified using a high-fidelity physics-based (HFPB) numerical modelling tool. CFDST columns are built in the nonlinear dynamic analysis program LS-DYNA and are comprehensively validated against experimental results in the aspect of column damage profiles and residual axial capacity of blast-damage columns. Extensive parametric studies are then carried out to investigate the effect of several key design parameters, i.e., charge weight, standoff distance, column diameter, nominal steel ratio, column height and axial load ratios, on the residual axial capacity of CFDST columns after subjected close-in blast loads. The results demonstrated good residual axial load-bearing performance of CFDST columns after subjected to close-in detonations of man-portable improvised explosive devices (MPIEDs). Based on the numerical analysis results, an empirical formula is derived to predict the residual axial load-bearing capacity of CFDST columns after experiencing close-in explosions. The proposed empirical formula can be utilized to quickly evaluate the vulnerability of close-in blast damaged CFDST columns.

Anti-blast performance of 3D-printed sandwich panels with auxetic hexagonal and regular hexagonal honeycomb cores

3D-printed auxetic honeycomb sandwich panels (HSPs) have considerable potential for blast resistance enhancement. This study aims to bridge the gap with regard to the experimental data on the effect of 3D-printed auxetic hexagonal honeycomb cores on the blast response of HSPs. To this end, the blast resistance of HSPs developed using auxetic re-entrant and regular hexagonal honeycomb cores is investigated experimentally and numerically. First, six HSPs are tested under close-in blast loadings. The HSPs comprise Q345 steel top and bottom sheets as well as a honeycomb aluminum alloy core with two configurations (regular hexagonal and auxetic re-entrant). According to the results, the former configuration enhances the HSP blast resistance by not only decreasing the deformation of the HSPs but also improving their damage tolerance. In addition, the responses of the HSPs are numerically studied via finite element analysis. The numerical method using the finite element program LS-DYNA achieves reasonable accuracy. Finally, a parametric study is conducted to investigate the effects of the honeycomb type, cell angle, debonding effects, and core material on the blast resistance of the HSPs. The results demonstrate that employing auxetic hexagonal honeycomb core, smaller cell angle, and ductile core material can improve the blast resistance of HSPs.