Blast Resistant Design Research Articles

Interaction of Blast Load on AASHTO Girder Bridge

Guidelines of blast resistant design for AASHTO girder bridges have not taken up much importance on researches. As the transportation infrastructure mainly bridges are highly vulnerable for bomb attack, they must be designed to resist it. The analysis and design of bridges subjected to blast load requires a detailed understanding of blast propagation and its dynamic effects on various structural elements. The response of bridge components subjected to blast load is carried out using Abaqus explicit finite element software. The bridge is modeled on the basis of AASHTO-LRFD bridge design specification for highway bridges. Blast load has been introduced on different critical location of the bridge to understand their effects on various structural elements and extent of damage. A thorough parametric study varying standoff distance and TNT mass is done to understand their importance in developing a blast resistant design for AASHTO Girder Bridge. The study concludes that the value of maximum displacement decreases with the increase in standoff distance.

Numerical study on the structural response of blast-loaded thin aluminium and steel plates

The inelastic response of thin aluminium and steel plates subjected to airblast loading is studied numerically and validated against experimental data. Special focus is placed on the influence of elastic effects and negative phase on the structural response. The blast loading was varied by detonating spherical charges of plastic explosives at various stand-off distances relative to the centre point of the plates. The numerical results obtained with the finite element code EUROPLEXUS were in good agreement with the experiments and predicted the entire range of structural response from complete tearing at the supports to a more counter-intuitive behaviour (CIB) where the final configuration of the plate was in the opposite direction to the incident blast wave due to reversed snap buckling (RSB). RSB attracted special attention since this is an unstable configuration sensitive to small changes in the loading and in structural characteristics. The negative phase of the blast pressure is usually neglected in blast-resistant design. However, the numerical simulations showed that the negative overpressure dominated the structural response and led to RSB at some loading and structural conditions. Two distinctive types of CIB were identified and both were found to depend on the timing and magnitude of the peak negative overpressure relative to the dynamic response of the plates. The study also revealed that CIB may occur in thin plates when the negative impulse is of the same order of magnitude as the positive impulse. The partial and complete failure along the boundaries observed in some of the tests was also successfully recreated in the simulations by using an energy-based failure criterion and element erosion.

Improved procedure for calculating the cleared pressure acting on a finite target due to a mid-field blast

For a structure subjected to it, a blast shockwave may be the severest load it will experience in its service life. A structure inadequately designed against blast may experience extensive damage and, in extreme cases, may collapse completely. Ensuring an adequate design depends on the accurate prediction of the blast shockwave and the loads it will impart on the structure. Blast shockwaves, however, are notoriously difficult to predict. The difficulties arise in part due to the reflected pressure and impulse developed by a blast shockwave depending on the obstacle’s response and geometry. Clearing is a result of the blast shockwave propagating around the edge of an obstacle, thus reducing the pressure build up from what would develop on an infinite surface. Thus, a clearer understanding of this phenomenon, and a simple practical method for predicting it, would improve blast load predictions and aid in blast resistant design. There are several experimental studies reported in the literature investigating this phenomenon. The studies, however, are limited to small scale blasts, and the prediction tools they propose are complicated to use. This article extends the range of available results numerically using ANSYS Autodyn, and proposes a tool to aid the blast resistant design engineer in more accurately quantifying the cleared blast loads imparted on a structure or structural element. Thus, after validating that Autodyn was suitable for investigating clearing problems, a series of two-dimensional models were built to investigate the parameters affecting clearing. The parameters investigated were the range, blast scaled distance, and distance to the edge of the target. The results of the numerical study resulted in a design aid for determining the cleared blast shockwave pressure on a finite target a given distance from the edge. The design aid proposed in this article is simple and applicable over a wide range of scaled distances.

Review of the current practices in blast-resistant analysis and design of concrete structures

In contemporary society, industrialization and rising of terrorism threats highlight the necessity and importance of structural protection against accidental and intentionally malicious blast loads. Consequences of these extreme loading events are known to be catastrophic, involving personnel injuries and fatalities, economic loss and immeasurable social disruption. These impacts are generated not only from direct explosion effects, that is, blast overpressure and primary or secondary fragments, but also from the indirect effects such as structural collapse. The latter one is known to be more critical leading to massive losses. It is therefore imperative to enlighten our structural engineers and policy regulators when designing modern structures. Towards a better protection of concrete structures, efforts have been devoted to understanding properties of construction materials and responses of structures subjected to blast loads. Reliable blast resistance design requires a comprehensive knowledge of blast loading characteristics, dynamic material properties and dynamic response predictions of structures. This article presents a state-of-the-art review of the current blast-resistant design and analysis of concrete structures subjected to blast loads. The blast load estimation, design considerations and approaches, dynamic material properties at high strain rate, testing methods and numerical simulation tools and methods are considered and reviewed. Discussions on the accuracies and advantages of these current approaches and suggestions on possible improvements are also made.

Influence of cylindrical charge orientation on the blast response of high strength concrete panels

Although a significant amount of research on the blast response of structural components has been conducted, scarce information is available on the effects of cylindrical charge orientation. Available literature mentioned that the orientation of a cylindrical charge with respect to the target structures can substantially influence blast wave parameters when compared to a spherical charge of same mass. Most standards and guidelines related to blast-resistant design are silent on this issue. Thus, an experimental study was conducted to investigate the effects of cylindrical charge orientation on the blast response of typical high strength concrete (HSC) flexural panels. Moreover, to obtain the reflected blast wave parameters, a steel plate with pressure sensors mounted on it was tested under the same blast loading conditions. The experimental results showed significant difference in the blast response of the panels (i.e., maximum mid-span displacement and failure mode) when the orientation of the cylindrical charge was changed from perpendicular to parallel with respect to the longitudinal axis of the test panels. Subsequently, the explosive as well as the air were modeled explicitly and in Arbitrary Lagrangian–Eulerian (ALE) air domain the blast wave propagated and impinged on a Lagrangian structure through fluid–structure interaction (FSI). After benchmarking the numerical reflected blast wave parameters against experimental results, three-dimensional nonlinear finite element (FE) model of the HSC panels was developed to predict the blast responses of HSC panels.

Blast resistance of tuff stone masonry walls

Gas explosions frequently occur in residential buildings inducing the out-of-plane collapse of single structural components which may trigger the progressive collapse of the structure. In this study, the out-of-plane collapse capacity of load-bearing tuff stone masonry (TSM) walls subjected to blast loading is investigated. A finite element macro-modelling strategy was adopted and dynamic analysis was carried out through LS-DYNA software to derive pressure–impulse diagrams for blast resistant design and assessment. Different modelling assumptions were considered. A sensitivity analysis allowed the evaluation of the influence of vertical pre-compression level and aspect ratio of TSM walls on blast collapse capacity. Numerical predictions of blast capacity were then compared to those provided by simplified analytical models, design code pressures and peak pressures estimated after real incidents.

Predictions of Structural Response to Dynamic Loads of Different Loading Rates

Owing to the increased terrorist bombing attacks, as well as accidental explosions associated with the rapid economic development and urbanization, more and more civilian structures might experience blast loadings in their service lives. These increase the demands of more structures being designed to resist certain level of blast loadings. As a result, some structural engineers with limited or no experience or training on structural dynamics nowadays might need to deal with analysis and design of structures against high-rate blast loads. Although design guides are followed, lack of fundamental knowledge of structural performance under high-rate loadings might not necessarily lead to accurate structural response predictions because the design guides normally only cover the most general and common blast loading scenarios and structural response conditions. Similarly, some researchers who have abundant experiences in analysis and design of structures under relatively low-rate dynamic loadings such as earthquake ground excitations intend to directly apply their experiences in earthquake engineering to blast resistant designs. This sometimes leads to inappropriate actions, e.g., adapting inter-storey drift as a performance criterion, using active control devices or cross bracing as a blast loading mitigation measure. This paper discusses the fundamental theory of structural dynamics, basic differences of structural responses subjected to low-rate dynamic and high-rate blast loadings. The accuracy of commonly used approaches in structural response analysis to blast loadings, i.e., the Single-Degree-of-Freedom analysis, will also be discussed.

Resilience Evaluation of Seismically Detailed Reinforced Concrete-Block Shear Walls for Blast-Risk Assessment

AbstractThe increased demand for resilient infrastructure under accidental or deliberate explosions has resulted in the urgent need to quantify the performance of both existing and new building components under such extreme loading events. The current study focuses on evaluating the resilience of reinforced masonry (RM) shear wall systems under blast, which is accomplished by quantifying the walls’ blast response in the out-of-plane direction and the resulting damage levels. In seismic zones, such RM walls are detailed to resist in-plane loads in a ductile manner, and thus minimal damage is usually expected. Given that blast resistant design of civilian buildings only recently has been formally introduced in North American design standards, quantifying the out-of-plane response and ductility capacities of RM shear walls has not been common practice in mainstream building design. In this paper, a nonlinear single-degree-of-freedom (SDOF) model is developed to predict the out-of-plane response of RM wall co...

Simplified Framework for Blast-Risk-Based Cost-Benefit Analysis for Reinforced Concrete-Block Buildings

Probabilistic risk assessment (PRA) is essential for evaluating different options for blast risk management. However, depending on the risk management approach being considered, a rigorous blast PRA study can be quite demanding. To expedite this process, a simplified PRA framework is proposed for reinforced concrete-block shear wall buildings, in order to determine design basis threat (DBT) fragility curves based on revised damage limit states most suitable for risk assessment. The current definitions of damage states by North American standards for blast resistant design involve global response limits--such as the support rotations of a structural element--that are relatively simple to calculate. However, such damage state descriptors can be insufficient for the cost-benefit analysis required to evaluate different risk mitigation options. As such, building on recent advances in the area of performance-based seismic design of concrete-block shear wall buildings, this study proposes revised damage states that can be associated with more useful metrics, including repair technique and building downtime. To illustrate the proposed methodology, a hypothetical shear wall building is analyzed under different DBT levels. The DBT fragility curves are obtained through Monte Carlo sampling of the random variables describing the shear wall system and are used to identify the locations that are most suitable for the erection of barriers for blast protection. The proposed PRA framework can be used to identify target performance requirements, formulated in terms of stakeholders' tolerable probability of failure and consequent risk management, for different classes of buildings under a range of DBTs. Language: en

Influence of Charge Shape and Point of Detonation on Blast-Resistant Design

AbstractCharts in technical manuals and standards of practice can be used to compute incident and reflected peak overpressures and scaled impulses generated by a detonation of a high explosive. Design values are reported for spherical free-air bursts and hemispherical surface bursts as a function of scaled distance and angle of incidence, where the charges are detonated at the center of the sphere. This paper describes a numerical study with a verified and validated computational fluid dynamics code that characterizes the influence of charge shape, charge orientation, and the point of detonation within the charge on free-field incident overpressures and impulses. Analyses are performed with cylindrical charges of different aspect ratios and masses, and results are compared with those of a baseline analysis of a spherical charge. In the near field and midfield, charge shape and point of detonation affect the peak overpressure and impulse, providing values that are significantly different from those associa...

Review of Glazing and Glazing Systems under Blast Loading

AbstractThe glazing and glazing systems of a building are the first part of a structure to be loaded in an external accidental and/or deliberate explosions; thus, it offers the first line of defense against these extreme loading conditions. Glazing fragments or shards remain a primary source of injury to occupants of buildings after explosive events. As a result, utmost effort must be placed in designing the glazing systems of a building against blast loading to minimize injury and damage. This paper provides an overview of blast loading, the types of glazing products, glazing construction, glazing systems, design objectives, approaches, performance and response criteria, and the code provisions related to the blast-resistant design of glazing and glazing systems used in buildings. In addition, test methods and retrofit strategies for glazing systems are succinctly discussed, and future research areas are highlighted.

강재압축재의 방폭성능에 대한 중력하중효과의 해석적 연구

Equivalent Single-Degree-of-Freedom(SDOF) analysis, most used for blast-resistant design, does not consider the effects of gravity load on the performance evaluation of blast resistance of structural members. However, since there exists gravity load on columns and walls of structures, the blast resistance of structural members should be evaluated considering gravity load on them. In this paper, an approach to reflect the gravity load effects on the equivalent SDOF analysis for dynamic blast response of structural members is proposed. For this purpose, the parametric studies using finite element analysis were performed by varying maximum blast load, blast load duration, and gravity load with constant the resistance and natural period of a structural member. The finite element analysis results were compared with the equivalent SDOF analysis results and the blast response of the structure member was estimated by conducting finite element analyses for various gravity loads. Finally, a graphical solution for ductility of a structural member with the variables of blast load, gravity load and structural member properties was developed. The blast response of structural members under gravity load could be estimated reasonably and easily by using this graphical solution.

Blast Design-Basis Threat Uncertainty and Its Effects on Probabilistic Risk Assessment

AbstractAt present, the deterministic approach to blast-resistant design appears to be the prevalent philosophy in practice, as suggested by the notion of design-basis threat (DBT) outlined by the ASCE/SEI 59-11. In this study, it is argued that even in the case of a clearly defined blast scenario, the resulting loading parameters can show a remarkably high degree of uncertainty, as corroborated by data from arena tests. Therefore, future standards should integrate a DBT definition guided by probabilistic risk assessment (PRA), in order to extend the general principles of limit state design philosophy to blast-resistant design. This paper investigates the sources of the variability observed in key blast wavefront metrics, including the peak pressure, specific impulse, positive phase duration, and decay coefficient. This objective is accomplished by quantifying and propagating the uncertainty associated with several input parameters, such as the mass of explosive, equivalent TNT–mass factor, pressure trans...

Inference of Blast Wavefront Parameter Uncertainty for Probabilistic Risk Assessment

AbstractProbabilistic risk assessment methodologies are typically employed to optimize resource allocations for blast risk mitigation schemes, which may be necessary for the design of new blast resistant facilities as well as the hardening of existing construction. A key aspect of any blast risk assessment methodology is the quantification of uncertainty inherent in the prediction of shock wave parameters. In this study, a blast pressure database that was generated from arena testing using live explosives is used to infer the probability distributions that best represent the model error affecting the prediction of four key wavefront parameters, namely: the peak pressure, specific impulse, duration, and waveform coefficient of the positive pressure phase. Confidence intervals are given for the descriptors of each distribution and their percentiles. In addition, two sets of partial factors are developed for the blast-resistant design of structures requiring high level of protection (LOP) based on a simplifi...

Failure Analysis and Damage Assessment of RC Columns under Close-In Explosions

AbstractBlast loads acting on structural components under close-in explosions are nonuniform; therefore, the damage to structural members under such blast loads is local and the failure mechanism is more complex as compared with that of distance explosions. Because of the lack of an accurate blast load model, a precise damage analysis method, an efficient damage assessment method, and practical protective measures, the blast-resistant design of structural members under close-in explosions faces great challenges. In this paper, a fluid-solid coupling numerical method is proposed and then used to investigate the failure mechanism of reinforced concrete (RC) columns under close-in explosions. The results show that local failure, such as crushing, cratering, and spall of concrete, is more likely to happen when the RC column is subjected to close-in blast loads. Parametric studies are carried out to investigate the influences of column dimensions and the reinforcement ratio on the damage degree of RC columns. ...

Study on Dynamic Responses and Reinforcement of Reinforced Concrete Columns Subjected to Blast Loading

The terrorism and regional conflicts posed a threat to the world peace. Some terrorist explosions caused collapse of the buildings, which brought heavy tragedies to the human components. Therefore research on damage of structural components and resistance to damage have become the focus of our attention. Finite element software LS-DYNA was applied to simulating the response of reinforced concrete columns under blast loading. And analysis on dynamic response under different loading period was carried out. By studying on the stress and strain of reinforced concrete columns subjected to blast loading, the possible failure modes were obtained. In addition, the bearing capacities of concrete columns that are reinforced with carbon fiber and steel panel were analyzed, and the reinforcement effects were compared to provide reasonable reinforcement schemes for structures blast-resistant design.

Impact of blasting parameters on vibration signal spectrum: Determination and statistical evidence

Research on the impact of blasting parameters on vibration signals is of significant value for guiding blast-resistant design. Previous research was primarily aimed at the impact on vibration amplitude in the time domain but rarely focused on energy distribution in the frequency domain (i.e., spectrum). Based on large amounts of blast signals from a series of events, in this study, the primary parameters that affect the vibration spectrum were determined. First, the K-means method was used to cluster all of the signals into six distinct spectrum clusters. The T test was then utilized among different clusters, to detect discrepancies in continuous parameters, including total charge, maximum charge, concrete age and distance between the explosion source and measuring point. Meanwhile, a random clustering simulation was conducted to determine whether the other two discrete parameters, i.e., the number of detonator relays and the explosion source location, influence the spectrums of vibration signals. The results show that three of the six parameters studied have a close link to the vibration spectrum, whereas the other three do not. This study also discusses how the parameters impact the occurrence and evolution of vibration signals.

Response Evaluation of Reinforced Concrete Block Structural Walls Subjected to Blast Loading

With the introduction of the new American and Canadian standards for blast resistant design, there is a need to evaluate the response of different structural components under such extreme loads. This paper focuses on experimentally evaluating the damage levels and the out-of-plane response of fully grouted reinforced concrete block structural walls under blast loading—a load that they are typically not designed to resist. The scaled walls reported in this paper cover a range of design parameters and charge weights that reflect different vulnerabilities and threat levels. Three different reinforcement ratios and three different charge weights have been used, with scaled distances as low as 1.61 m/kg1/3 and two different boundary conditions, to evaluate the walls’ response. In general, the results show that the walls are capable of withstanding substantial blast load levels with different extents of damage depending on their vertical reinforcement ratio and scaled distance. However, brittle behavior was observed in the walls with a reinforcement ratio higher than 0.6%. This is attributed to the fact that seismically detailed (concrete or masonry) structural walls designed to respond in a ductile manner under in-plane loads might develop brittle failure under out-of-plane loads. This is a consequence of the increased concrete block wall reinforcement ratio in the out-of-plane direction compared with the same in the in-plane direction. The maximum experimental support rotation values were compared with the corresponding values predicted using an available nonlinear single-degree-of-freedom (SDOF) model presented in the Unified Facilities Criteria document. In general, the comparison between the experimentally obtained and the analytically predicted support rotation values indicated reasonable agreement. The test results are expected to contribute to the growing masonry blast performance database of experimental results and to the future development of reinforced concrete block wall design provisions under blast loading in North America, in which a balance between the wall strength and ductility might be necessary to remain below the different damage classifications specified by the performance-based design oriented ASCE and Canadian Standards Association (CSA) standards.

Blast Testing of Cold-Formed Steel-Stud Wall Panels

AbstractCold-formed steel-stud walls have been utilized as an attractive option for blast-resistant design due to the combination of high strength and ductility that enable them to absorb and dissipate blast energy through large deformation kinematics. However, achieving the available ductility of the steel studs requires special attention to the stud-to-track connection details, which has remained an active area of research and development. While much of the existing literature has described specialized ideal boundaries to ensure that the full tensile membrane response of the studs would be achieved prior to connection failure, the research reported in this paper examines the blast performance of cold-formed steel-stud walls with commercially available connections and bridging. Experimental results from a series of three open-arena blast tests of identical cold-formed steel-stud wall panels are presented. Distortional buckling of the studs around unstiffened punchouts in the web as well as web crippling ...

Blast resistant design of precast reinforced concrete walls for strategic infrastructures under uncertainty

Extreme loads can have devastating effects on civilian structures since these buildings are not designed to withstand extreme events. Typical buildings and other critical infrastructures are particularly prone to external man-made attacks. This study focuses on probabilistic analyses, and investigates the probability of exceeding a given limit state of a precast concrete wall subjected to blast loads. The wall under investigation is a non-load bearing precast concrete panel used as exterior cladding for buildings. From the blast design point of view, these walls must protect people and equipment from external detonations. The aim of the paper is to compute both the fragility curves and the probability of exceedance of a typical precast concrete cladding system, considering a prescribed detonation of a vehicle borne improvised explosive device. To this aim non-linear dynamic analyses are carried out by the widely adopted equivalent single degree of freedom method. The fragility curves and the probability of exceedance of the precast concrete cladding wall are computed using Monte Carlo simulations.