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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. • Eight ML models are used to predict the residual bearing capacity damage index of RC columns under blast loads. • After a detailed comparison of the prediction abilities, the best ML model is selected. • The coupling relationship between the axial compression ratio and scaled distance on the damage index is analyzed. • The zonal map for rapid assessment of RC column blast damage is obtained. [ABSTRACT FROM AUTHOR]

Laminated insulating glass units (IGUs), commonly used in modern buildings, are prone to shattering from explosive loads, causing significant damage and loss. Existing research on IGUs is constrained by a lack of experimental validation and comprehensive numerical analyses, as large-scale explosion tests are rarely reported due to safety and cost concerns. Furthermore, previous modeling efforts often oversimplify critical factors such as the supporting structure, component interactions, strain rate effects, hourglass energy, and failure criteria, leading to an inadequate representation of glass behavior under explosive loads. This paper addresses these gaps by conducting large-scale explosive test on glass system and utilizing sophisticated nonlinear dynamic analysis with LS-DYNA for simulation. The research considers the influence of the support system and incorporates detailed considerations of component interactions, constitutive relationships, and strain rate effects in the numerical simulations. The results confirm that the proposed model successfully replicates the crack patterns and damage observed in experimental test. Also, it accurately predicts the trajectory, quantity, and size distribution of glass fragments. The proposed modeling approach offers a more informed assessment of damage and improves the evaluation of glass safety in practical applications. • A full-scale explosive testing of laminated insulated glass units (IGUs) provides valuable data for simulation model development. • An advanced finite element model is provided for accurate assessments of glass blast resistance. • The Johnson-Holmquist 2 material model is validated for accurately simulating glass behavior under high-speed impacts. • Explosion-proof performance levels of insulating laminated glass are quantified under large explosion conditions as per related standards. [ABSTRACT FROM AUTHOR]

In this paper, a new mechanical model including initial geometric imperfection is developed to investigate the nonlinear transient response of graphene platelets reinforced metal foams (GPLRMF) blades subjected to blast load. Combined with higher-order shear deformation plate theory (HSDT) and von-Karman geometric nonlinearity, the nonlinear motion equations are established, in which the Coriolis force, centrifugal force as well as initial geometric imperfection are simulated. Considering cantilever boundary condition, the partial differential equations are transformed into a series of ordinary differential equations by Galerkin discretization. Using the four order Runge-Kutta algorithm, the nonlinear transient response is numerically researched, and the time histories and phase trajectories are obtained. In addition, the effectiveness of the current research is validated by comparing the results with the existing valuable literatures. The influences of rotating speed, presetting angle, initial geometric imperfection, material property, damping coefficient, and blast load parameter on the dynamic deflection and instantaneous speed are presented. Numerical results reveal that the nonlinear transient dynamics of the composite blades under blast load are significantly influenced by initial geometric imperfection. • Build a mathematical model for the rotating blades with initial geometric imperfection. • Consider the impacts of the blast load, rotating motion and presetting angle. • Illustrate the nonlinear transient responses of the rotating blades. • Employ the Runge-Kutta approach to acquire the numerical results. [ABSTRACT FROM AUTHOR]

Blast loading and seismic excitations are widely recognized as the most detrimental occurrences that a building structure may encounter throughout its lifespan. Therefore, this study investigated the retrofitting capacity of external devices (ENTA damper systems) for reinforced concrete (RC) frames in term of enhancing their resistance under the combined effects of blast and seismic loads. This study presents the establishment of finite element (FE) models for retrofitted RC frames with ENTA damper systems through the utilization of the dynamic analysis software LS-DYNA. The investigation involved the validation for blast performance of RC column in order to identify the most effective method for modeling blasts. Additionally, the study aimed to validate the performance of RC frame models through effects of ENTA damper systems under seismic loading. Subsequently, a performance evaluation of RC frame structures was carried out to examine the impact of the ENTA damper systems when subjected to blast loading. The findings of the study indicate that the use of external ENTA damper systems effectively enhanced the rigidity and structural integrity of RC frames, while maintaining their ability to resist deformation. Finally, the damage assessment of blast and seismic performance is investigated based on various parameters such as ductility, drift and energy-based damage limits. • Finding the suitable model blasts based on the blast performance of RC column. • Validating performance of the RC frame models under seismic loading. • Investigating the blast performance of RC frame and retrofitted RC frame. • Considering the damage performance of RC frames under blast and seismic loadings. [ABSTRACT FROM AUTHOR]

• Summary of up-to-date field experiments of blast load action on structural elements. • Design modification is "pre-strengthening" against blast in designing and planning. • Retrofitting implies mitigation of blast effects using additional strengthening. • Innovative materials with specific characteristics are used for blast load mitigation. • Majority of materials were able to decrease or even completely prevent flying debris. The number of intentional and unintentional explosions is constantly increasing worldwide. Owing to increasing threat, the need for safer structures is of utmost importance. This paper summarizes and systematizes the studies conducted on blast load mitigation. The studies on design and retrofit methods utilize experimental investigation. The results obtained through field tests approximately represent real-life situations. The research included a wide variety of materials, which are used for the design and retrofit of structural elements, ranging from fiber-reinforced to externally retrofitted concrete. Tests showed high potential of all applied methods for increasing blast resistance by enhancing structural strength and ductility, and by reducing or even preventing flying debris. [ABSTRACT FROM AUTHOR]

Avoiding steel-bar-like corrosion in concrete members, basalt fiber reinforced plastic (BFRP) bars behaving as reinforcement have advantages in coastal civil engineering. One-way concrete slabs reinforced by BFRP bars (SRBBs) were designed to investigate their mechanical responses under static loads and explosions. High strength but relatively low stiffness of BFRP bars make SRBBs have different responses to slabs reinforced by steel bars (SRSBs). BFRP bars work in the elastic stage while steel bars result into plastic deformation after limited elastic deformation. SRBBs have larger deflections but higher ultimate loads compared with SRSBs in static bending tests. Explosive experiments reveal the damage patterns of SRBBs under various scaled distances, from 0.474 m/kg 1/3 to 0.684 m/kg 1/3 . Crack, spall and breach are three typical damage modes for blast-loaded slabs. Compared with SRSB, the SRBB of the same reinforcement ratio and under the same scaled distance has larger deflections, but smaller damage level and greater residual loads. It is indicated that although the SRBB is not stiffer than the SRSB, it has greater anti-blast ability in current research. [ABSTRACT FROM AUTHOR]

To study the effect of blast pressure on structural resistance against progressive collapse under column removal scenario induced by contact detonation, and to investigate the development of catenary action within ultra-fast dynamic regime, a physics-based finite element model is developed in this paper. The model is first validated by a quasi-static test series on reinforced concrete sub-assemblages under middle column loss assumption and a blast test series using the same structural configurations. The sub-assemblage included a two-span beam, a middle column stub and two column stubs at both sides. Besides validations with sub-structure tests, some pull-out tests are also performed to verify the numerical models. After the verifications, parametric studies are conducted to investigate the influence of important dynamic and structural factors such as the boundary stiffness, damping ratio, and charge weight attached to the middle column. The study shows that under actual blast conditions, catenary action in sub-assemblages can be mobilised to prevent a structure from collapse even when the bottom longitudinal reinforcement in the bridging beam has already fractured. Moreover, stiffness of horizontal restraints plays an important role to mitigate disproportionate collapse in both static and blast conditions. A comparison is also made between nonlinear dynamic procedure and nonlinear static analysis incorporating simplified energy method for dynamic assessment. It is concluded that the simplified static approach in lieu of dynamic analysis can be considered as a conservative method for practical design purpose. Nonetheless, this method may over-estimate structural resistance if the localised damage is induced by a contact-detonation event. [ABSTRACT FROM AUTHOR]

Over the past several decades, iconic and public buildings have become targets of terrorist bomb attacks, but most of these buildings were built without consideration of blast loading scenarios. Key load-carrying elements such as concrete columns are probably the most critical structural components for structural protection against bomb threats. Failures of columns may trigger catastrophic progressive collapse if there is insufficient structural redundancy. In a recent study, novel ultra-high performance concrete (UHPC) material formulated based on reactive powder concrete (RPC) was developed. Field blast tests on columns made of this material were performed. Test results showed that UHPC columns had excellent blast resistant capability, only small mid-height deflection and minor concrete damage was observed after the blasting tests. In the present study, to quantify blast-induced damage and assess residual loading capacity of UHPC columns, static axial loading tests on post-blast UHPC columns were carried out. Undamaged control samples were tested to provide benchmarks. Damage index and residual loading capacity of UHPC columns after various blast loadings were obtained. It was found that column cast with micro steel fibre reinforced UHPC preserved more than 70% of its loading capacity after 35 kg TNT detonation at 1.5 m standoff distance, while high strength concrete column only maintained 40% loading capacity after 8 kg TNT detonation at 1.5 m standoff distance. [ABSTRACT FROM AUTHOR]

• A multi-objective optimisation model was developed by combining a validated numerical model, RBF neural network, and genetic algorithm. • The obtained optimum auxetic design with respect to protection performance exhibited two deformation modes and two plateau stress levels. • A higher magnitude and more stable negative Poisson's ratio was observed in the optimum auxetic design. • The optimised design offered superior blast protection in comparison to the initial baseline design. This paper aims to optimise a bulk scale design of a novel auxetic structure, the hourglass structure (HGS), through a multi-objective optimisation model to improve its protection performance. A 3D numerical model of the HGS under an in-plane quasi-static compression was developed and validated with experimental results. Based on the validated numerical model, a series of numerical analyses were conducted by automating the HGS design process with randomly generated design variables. The automated numerical analyses built a dataset of the selected protective performance indicators (namely, peak elastic stress, plateau stress, and energy absorption capacity). Then, the dataset was used to develop a high-accuracy surrogate model using a radial basis function (RBF) neural network. Afterward, the Pareto optimal solutions were searched with the non-dominated sorting genetic algorithm (NSGA-II). The best compromise design out of the Pareto optimal set was determined with the ideal point method. The performance of the optimum design was simulated under both quasi-static and blast loadings to comprehensively explore the protective performance. In addition, a correlation matrix was constructed to investigate the effects of each design parameter on the protective performance indicators quantitatively. The results showed that the obtained optimum design outperformed the baseline structure under both quasi-static and blast loadings. The optimum HGS design displayed a higher and more stable negative Poisson's ratio along with two deformation modes leading to two plateau stress levels. The optimised HGS design is applicable as the core of high-performance protective sandwich structures. [ABSTRACT FROM AUTHOR]

• Performance of ECC monolithic and composite slabs under near-field blast was tested. • ECC monolithic and composite slabs exhibited ductile response under near-field blast. • No spalling occurred even ECC monolithic and composite slabs underwent large deformation and failed. • Both ECC monolithic and composite slabs exhibited favorable performance under near-field blast. To improve the performance of reinforced concrete (RC) structural members subjected to blast, especially the spalling due to the brittleness of concrete, engineered cementitious composite (ECC) was applied in monolithic and composite slabs and their responses subjected to near-field blast were experimentally investigated in the present study. First, two different ECC materials were prepared and tested with quasi-static direct tension and flexural tests, whose results showed significantly improved tensile ductility and strength compared to normal concrete. Then a field test was conducted to investigate the response of ECC monolithic and composite slabs under near field blast, with an RC slab as reference. The responses of these slabs were compared in terms of response mode, residual deformation, crack initiation and development, spalling, strain time history, etc. The test observations suggested that in addition to the ductile response and failure of ECC subjected to quasi-static direct tension and flexural tests, ECC still exhibited ductile response at high strain rate when applied in monolithic and composite slabs under near field blast. Compared to the perforation and spalling of RC slab, the ECC monolithic or composite slabs underwent large deformation, until collapse failure with a major crack in the mid-span occurred. Importantly, throughout the whole response process, even the ECC monolithic and composite slabs collapse with a major crack at mid-span, no spalling was observed. Furthermore, no delamination occurred in the interface between the RC and ECC layer of the RC/ECC slabs. Both the ECC monolithic slab and RC/ECC composite slab exhibited favorable performance subjected to near-field blast. These observations implied that the ECC is promising in the potential application of structural protection against blast, not only for replacing certain key components in the newly built structures but also for retrofitting existing RC structures. [ABSTRACT FROM AUTHOR]

This article presents a fracture mechanics-based numerical approach for quantifying delamination of spray-applied fire-resistive material (SFRM) from a steel beam–column subjected to a blast loading. In the numerical model, cohesive zone model is employed to simulate interfacial crack initiation and propagating at the interface of SFRM and steel. Three types of SFRM, widely utilized in the practice namely, mineral fiber-based, gypsum-based and Portland cement-based SFRM are considered in the analysis. The numerical model is validated against two sets of experiments; a full scale blast test on a steel beam–column and a drop mass impact test on a steel beam insulated with SFRM. The verified numerical model is subsequently utilized to carry out extensive parametric study to quantify critical factors that can influence the extent of delamination of SFRM from a steel beam–column, namely fracture energy at steel-SFRM interface, elastic modulus of SFRM, thickness of SFRM, and the level of blast overpressure. Results from parametric studies show that Portland cement-based SFRM can provide the highest level of resiliency in terms of withstanding the applied blast overpressure, while mineral fiber-based SFRM shows the lowest level of endurance. Further, the outcomes obtained from parametric study demonstrate that the extent of delamination can directly be related to blast overpressure and thickness of SFRM, whereas it can inversely be related to elastic modulus and fracture energy of SFRM. Based on the results of parametric study, a delamination characteristic parameter, which incorporates the major factors influencing the delamination, is defined and the extent of delamination is expressed as a function of this parameter. [ABSTRACT FROM AUTHOR]

Highlights: [•] One dimensional finite element model incorporating direct shear behavior. [•] Member and direct shear response of RC slabs subjected to blasts. [•] Parametric study on direct shear PI curves for RC slabs. [•] Investigation of flexural member behavior on direct shear response. [Copyright &y& Elsevier]

Highlights: [•] Influence of ground shock rise time on assessing in-structure shock is investigated. [•] A small-scale test is conducted to validate the theoretical prediction. [•] In-structure shock level with rise time considered is higher for a typical event. [Copyright &y& Elsevier]

Highlights: [•] A novel approach to simplify the fully confined blast loads was developed in this manuscript. [•] Centroid of the confined blasts is the key factor affecting structural response. [•] This simplification method can be used for analysing response of ductile structural members. [Copyright &y& Elsevier]

Abstract: In-structure shock poses a great threat to equipment and devices in underground protective structures, preventing them from accomplishing designed tasks. Unlike traditional mitigation methods such as backfilling soft soil or sand around the buried structures and adding shock-isolation cushions to the equipment, a new structural design of underground structures are proposed by constructing an isolation slab, to which the equipment is attached. The excitation mechanism for the equipment attached to the slab is altered from the combination of flexural deflection and rigid body motion of the traditional floor to the response of the isolation slab. Analysis indicates that vertical shock level experienced by the equipment is effectively reduced. The in-structure shock mitigation approach proposed in the present study provides a supplement to the existing shock mitigation methods for underground structures. [Copyright &y& Elsevier]

Abstract: When an underground structure is subjected to a subsurface explosion, an in-structure shock occurs. The in-structure shock can be a major cause of disruption and even damage to the instruments and equipment contained in the structure if the detonation is relatively distant. For this reason, an appropriate analysis and prediction of explosion-induced in-structure shock is an important topic in the area of protective design of underground structures. In this paper, a detailed analysis is conducted on a representative buried structural element subjected to soil-transmitted blast. The soil–structure interaction is considered by introducing an interfacial damping between the structural element and the surrounding soil. Two phases of the structural response to the blast load, i.e., a blast loading phase and a free-vibration phase, are analyzed. Based on the analytically derived time histories of the structural response, which represent the in-structure shock, the response spectra concerning the equipment (sub-structures) attached to the main structure are constructed. Besides providing a theoretical approach for the evaluation of the in-structure shock and its subsequent effects, the present analysis is supplementary to the relevant provisions in TM5-855-1 and TM5-1300, in which only rough predictions of in-structure shock for buried structures are specified. [ABSTRACT FROM AUTHOR]

• Develop P–I models for FRP retrofitted RC columns to predict and assessment of blast damages. • Proposed a new method to determine the damage index to identify the capacity degradation of the RC columns when exposed to extreme loads. • Applied LBE function to simulate blast loads in RC columns retrofitted with FRP composite. • Validation of numerical simulation of FRP strengthened RC column compare to experimental blast field test. The efficiency of fibre reinforced polymer (FRP) in strengthening the concrete structure against blast loads is investigated for RC columns exposed to blast loads. It should be mentioned that no systematic investigations derived pressure and impulse (P-I) models for FRP retrofitting RC columns in the literature. Thus, the primary goal of this project is to construct a finite element model that will offer data for the development of a P-I diagram that can be utilized to mitigate blast threats and predict damage in RC columns retrofitted with FRP. Another aspect of the present work is to propose a new technique to determine the damage index to identify the capacity degradation of the RC columns when exposed to extreme loads in the current research various strengthening schemes are quantitatively tested against blast loads by doing LS-DYNA software. Numerical simulation of blast load is implemented by using Load-Blast-Enhanced (LBE) technique. The models are validated through experimental work to assess the correctness of model simulations in order to illustrate the models behavior. The structural behavior of un-strengthened RC columns was compared to the structural behavior of various columns retrofitted with varying FRP wrap thickness, strength, and arrangement. The simulations revealed that strengthening columns with FRP is a viable strategy to improve their explosion resistance capability, and that retrofit procedures are useful in minimizing the building's hazard. Engineers can utilize the P–I curves obtained to assess the damage levels of new columns and to estimate the damage levels of existing columns subjected to different extreme load scenarios. [ABSTRACT FROM AUTHOR]

Abstract: The purpose of this study is to construct and validate a finite element model for predicting the response of soil-filled concertainers subjected to blast loading based on experimentally measured displacement–time histories. The concertainers are foldable welded-wire mesh geotextile-lined cubical connected baskets. When filled with soil they form thick protective walls and structures. Three full-scale experiments consisting of air-blast loading simple free-standing soil-filled concertainer walls were conducted at DRDC Suffield and reported in this paper. The pressure–time histories of the blast loads and displacement–time histories of walls were recorded. Soil densities and moisture contents were measured. Soil samples were collected and specimens were prepared to the closest conditions experienced in the field. The specimens underwent a series of UU triaxial tests to obtain soil properties used in a finite element analysis. This finite element model was formulated using the LS-Dyna software. The numerical responses of the walls obtained from the analysis were compared with the experimentally measured responses. A good agreement was achieved. The numerical model of a soil-filled wall demonstrated slightly lower blast resistance than the experimental results. Various sources of discrepancies are discussed. The study helps to provide a good understanding of the response and the failure mechanism of the walls, and is useful in the development of analytical models for design purposes. [Copyright &y& Elsevier]

The analysis of the structural failure of a reinforced concrete building caused by a blast load is presented in this paper. All the process from the detonation of the explosive charge to the complete demolition, including the propagation of the blast wave and its interaction with the structure is reproduced. The analysis was carried out with a hydrocode.The problem analysed corresponds to an actual building that has suffered a terrorist attack. The paper includes comparisons with photographs of the real damage produced by the explosive charge that validates all the simulation procedure. [Copyright &y& Elsevier]

• Numerical simulation algorithms and material models are validated by field explosion tests. • High-reliability FE model of prototype RC girder bridge was established and the damage modes are revealed. • Damage modes and responses of simply-supported and continuous RC girder bridges are compared. • The minimum safe standoff distances for below-deck explosions are given for bridge protections. During the whole service life, bridge structures potentially suffered from the threats from military conflicts, terrorist attacks and accidental explosions. The related studies on the damage modes and dynamic responses of entire RC girder bridges subjected to the explosion loadings is very limited, which is addressed through high-reliability numerical simulations. Firstly, by comparing with the experimental overpressure- and acceleration-time histories, as well as the damage modes from the explosion tests on 1/5 scaled two-span girder bridges, the validities of the material models and corresponding parameters, as well as the numerical simulation algorithms are verified sufficiently. Then, three levels of potential explosive threats, i.e., suitcase, sedan, and small moving van (the corresponding equivalent cubic TNT explosive masses are 23 kg, 454 kg and 4536 kg) specified by Federal Emergency Management Agency (FEMA) were selected to analyze the damage modes and dynamic responses of a typical four-span prototype RC girder bridge under both below- and above-deck explosion scenarios. Furthermore, the blast resistance of both simply-supported and continuous girder bridges were examined, and the minimum safe distances were proposed. It derives that, (i) for the below-deck explosion scenarios, total nine damage modes exist from small-scale spalling of concrete at the bottom of pier to the total collapse of the bridge; (ii) for the above-deck explosion scenarios, eight damage modes can be induced, including cratering and opening in deck, flexural failure of the T-girder, etc.; (iii) the continuous bridge exhibits obvious and slight enhanced blast resistance for below- and above-deck explosions than simply-supported girder bridges; (iv) small moving van can lead to the destruction of the entire bridge, the minimum safe standoff distances for suitcase and sedan bombs are 0.5 m and 3.0 m. [ABSTRACT FROM AUTHOR]

• Structural response of reinforced concrete silos to blast loads. • CONWEP and Coupled Eulerian – Lagrangian methods for blast load simulation. • Nonlinear dynamic analysis with damage-based criteria. • Strain rate and dynamic material properties. • Blast energy absorbed by the silos. Extensive research work has been conducted to study the structural behavior of silos for various static load types; namely the grain load compression phases inside the silos and the thermal loads. However, very few investigations were related to the effect of different dynamic loads on silos, especially shock and blast loads. The aim of this research is to evaluate the structural response of grain silos due to massive blast loads. The Beirut explosion that occurred on August 04, 2020 is considered as a case study in a structural engineering approach with numerical non-linear finite element modeling of the silos. Due to the uncertainty of the exploded material mass, the magnitude of the explosion is defined as the numerical model magnitude that generates the same silos damages and sways recorded on site. The numerical study models are based on silos data (geometrical and material properties), and the use of the Conventional Weapons Effects Blast Loading (CONWEP), and the Coupled Eulerian-Lagrangian (CEL) methods to generate the blast loads. In addition, damage for the standing silos has been assessed, and final recommendations were stated. The results of this study define the magnitude of the explosion and the structural state of the remaining silos. [ABSTRACT FROM AUTHOR]