Design Of Blast Resistant Structures Research Articles

Experimental and numerical study on the blast performance of the corrugated double steel plate concrete composite wallboard under blast loads

The corrugated double steel plate concrete composite wallboard (CDSCW) exhibits superior axial compressive load-bearing capacity, lateral flexural stiffness, impact resistance, and seismic performance compared to the traditional reinforced concrete wallboard and plane double steel plate concrete composite wallboard (PDSCW). Therefore, it has great potential application in offshore engineering and military engineering. This study designs and fabricates two types of CDSCW specimens. Firstly, a comparative analysis is conducted to examine the damage patterns and dynamic responses of the two specimens under near-field explosion experiments. Secondly, the damage mechanisms and explosion response of CDSCW and PDSCW subjected to close-in explosions are numerically investigated by using ANSYS/LS-DYNA, and the results are then compared with experimental findings. Parameter analysis is performed to assess the influence of concrete thickness, steel plate thickness, and explosive charge on the blast resistance of CDSCWs. Furthermore, a nonlinear resistance equation and an equivalent single degree of freedom (ESDOF) theoretical model for simply supported beams is established to predict the dynamic response of CDSCWs under near-blast loads. This theoretical model considers the constitutive model of bilinear materials and the effect of plastic hinges. The reliability of the proposed theoretical model is verified by comparing the residual deflection of CDSCWs obtained from explosion tests with validated numerical simulation results. The results demonstrate that the CDSCWs, with the same concrete and component dimensions (length, width), exhibit greater flexural stiffness and superior energy dissipation capacity subjected to close-in explosion. Moreover, their blast resistance significantly surpasses that of PDSCWs. In particular, an increase in corrugation depth effectively improves the blast resistance of CDSCWs. The dynamic response equations, based on the established elastic-plastic model and primarily considering bending deformation of the components, precisely predict the dynamic response of simply supported CDSCWs under near-blast loads. consequently, these findings can provide a robust foundation for further research and the design of blast-resistant structures.

Modeling destructive effects of an explosion in an urban environment using ANSYS AUTODYN

Purpose is to study the impact of explosive waves in an urban environment using comprehensive numerical modeling. A series of simulations were conducted using ANSYS AUTODYN software, allowing us to accurately replicate the dynamics of explosive wave interactions with urban structures. The methods used involves calculations through modeling and analysis of results. The obtained research results demonstrate that the application of numerical modeling with ANSYS AUTODYN allows for highly precise prediction of the influence of explosive waves on urban structures. These methods effectively model complex interactions between explosive waves and the urban environment, providing valuable information for safety measures and urban structure design. Findings. Results demonstrate that the application of numerical modeling with ANSYS AUTODYN allows for highly precise prediction of the influence of explosive waves on urban structures. These methods effectively model complex interactions between explosive waves and the urban environment, providing valuable information for safety measures and urban structure design. The originality lies in the combination of 2D and 3D modeling for a detailed analysis of explosive events in urban conditions, expanding existing knowledge about the interaction of explosive waves with urban infrastructure. Based on the obtained data, measures can be developed to enhance the safety and resilience of urban infrastructure in the event of explosive events, as well as to improve urban environment planning and protection. Practical implementation. Based on the obtained data, measures can be developed to protect urban structures from potential explosive events, including the design of blast-resistant structures, optimization of urban plans considering potential risks, improvement of evacuation systems, and enhancing safety for the civilian population in densely populated areas.

Temporally and Spatially Resolved Reflected Overpressure Measurements in the Extreme Near Field.

The design of blast-resistant structures and protective systems requires a firm understanding of the loadings imparted to structures by blast waves. While empirical methods can reliably predict these loadings in the far field, there is currently a lack of understanding on the pressures experienced in the very near field, where physics-based numerical modelling and semi-empirical fast-running engineering model predictions can vary by an order of magnitude. In this paper, we present the design of an experimental facility capable of providing definitive spatially and temporally resolved reflected pressure data in the extreme near field (Z<0.5 m/kg1/3). The Mechanisms and Characterisation of Explosions (MaCE) facility is a specific near-field evolution of the existing Characterisation of Blast Loading (CoBL) facility, which uses an array of Hopkinson pressure bars embedded in a stiff target plate. Maraging steel pressure bars and specially designed strain gauges are used to increase the measurement capacity from 600 MPa to 1800 MPa, and 33 pressure bars in a radial grid are used to improve the spatial resolution from 25 mm to 12.5 mm over the 100 mm radius measurement area. In addition, the pressure bar diameter is reduced from 10 mm to 4 mm, which greatly reduces stress wave dispersion, increasing the effective bandwidth. This enables the observation of high-frequency features in the pressure measurements, which is vital for validating the near-field transient effects predicted by numerical modelling and developing effective blast mitigation methods.

Modeling the blast load induced by a close-in explosion considering cylindrical charge parameters

Structural damage is significantly influenced by the various parameters of a close-in explosion. To establish a close-in blast loading model for cylindrical charges according to these parameters, a series of field experiments and a systematic numerical analysis were conducted. A high-fidelity finite element model developed using AUTODYN was first validated using blast data collected from field tests conducted in this and previous studies. A quantitative analysis was then performed to determine the influence of the charge shape, aspect ratio (length to diameter), orientation, and detonation configuration on the characteristics and distributions of the blast loading (incident peak overpressure and impulse) according to scaled distance. The results revealed that the secondary peak overpressure generated by a cylindrical charge was mainly distributed along the axial direction and was smaller than the overpressure generated by an equivalent spherical charge. The effects of charge shape on the blast loading at 45° and 67.5° in the axial plane could be neglected at scaled distances greater than 2 m/kg1/3; the effect of aspect ratios greater than 2 on the peak overpressure in the 90° (radial) direction could be neglected at all scaled distances; and double-end detonation increased the radial blast loading by up to 60% compared to single-end detonation. Finally, an empirical cylindrical charge blast loading model was developed considering the influences of charge aspect ratio, orientation, and detonation configuration. The results obtained in this study can serve as a reference for the design of blast tests using cylindrical charges and aid engineers in the design of blast-resistant structures.

A comparative performance of columns: reinforced concrete, composite, and composite with partial C-FRP wrapping under contact blast

Damage to government buildings, iconic structures, and monuments from blast incidence of global terrorism and accidental explosions are perpetually attracting the attention of researchers. Devastating consequences associated with such a disastrous event of explosion inflict significant fatalities and huge economic losses. Efforts are being made by engineers and architects in the domain of blast-resistant design of structures to control the ensuing damage out of explosions. In the present study, an experimentally tested square reinforced concrete (RC) column with seismic lateral reinforcement carrying axial load subjected to an explosive charge of 100 kg ANFO (82 kg-TNT-equivalent) at a scaled distance of 1.0 m/kg1/3 with 10 mm mesh size using the ABAQUS/CAE software equipped with concrete damage plasticity model is validated. Not many studies are available on the structural elements subjected to contact blasts. Columns being the most important load-carrying structural elements of the buildings, the effort is made to study the effect of contact blasts on the validated model. An RC composite column equivalent to the experimentally tested one is considered to enhance its blast response under contact blast. The composite column is further strengthened with C-FRP wrapping over the mid-height region subjected to the same blast loading. Performance of RC column, its equivalent composite column, and the equivalent composite column with partial C-FRP wrapping are analyzed and compared. In comparison of the RC column with top and bottom seismic reinforcements, maximum displacement and DDE of the equivalent composite column having top, bottom, and middle seismic reinforcements without C-FRP wrapping reduced by 61.21% and 48.12%, respectively. The percentage reductions of these values of the composite column with the wrapping are 89.93% and 87.03%, respectively. This research shows that the composite column with top, bottom, middle seismic reinforcement and with C-FRP wrapping gives the best performance under contact blast.

Experimental study on TNT equivalent coefficients for two new kinds of propellants

The TNT equivalent coefficient is an important evidence to guide the blast-resistant design and safe-distance determination for dangerous goods. To find out the TNT equivalent coefficients of two new kinds of propellants (H1, H2), a series of free-field static detonation tests were performed for the two propellants (H1, H2) and flaky 2,4,6-trinitrotoluene (TNT). Five repeated tests were carried out for each explosive and the mass of the tested explosive was 10 kg in each test. And the existing method for calculating the TNT equivalent coefficients was modified. Base on the overpressure-time curves of the shock waves at different distances from the explosion centers, the TNT equivalent coefficients for overpressure and specific impulse at different scaling distances were analyzed by the modified calculation method. The results show that the propagations of shock waves induced by explosions of the propellants agree well with the similar law, and are similar with that induced by explosion of the TNT explosive. Meanwhile, the overpressures and specific impulses of shock waves induced by explosions of the two propellants are much higher than those of the TNT explosive. With the increase of scaling distance, the overpressure TNT equivalent coefficient of H1 first increases to 1.34 and then decreases, while that of H2 decrease monotonously, and the maximum value is 1.26. With the increase of the scaling distance, both the specific impulse TNT equivalent coefficients of H1 and H2 first increase and then decrease. The specific impulse TNT equivalent coefficient of H1 with the peak value 1.38 is greater than that of H2. The modified method can be used to accurately calculate the TNT equivalent coefficients of the tested samples, and the results can improve the safety design of blast-resistant structures.

Blast Loaded Columns—State of the Art Review

The ever-present threat of terrorist attacks in recent decades gives way to research towards blast-resistant design of structures. Columns, as one of the main load-bearing elements in residential buildings and bridges, are becoming interesting targets in bombing attacks. Research of column blast load behavior leads toward increased safety by identifying shortcomings and problems of those elements and acting accordingly. Field tests and numerical simulations lead to the development of new blast load mitigation technics, either in the design process or as a retrofit and strengthening of existing elements. The article provides a state-of-the-art literature review of filed blast load tests and numerical simulations of a bridge and building columns.

Probabilistic framework for failure investigation of reinforced concrete wall panel under dynamic blast loads

Over the last decade, excessive devastations caused by extreme events, such as blast loading have raised significant concern on the performance of civil structural systems. Despite realizing the importance of inherent risk associated with this phenomenon, most of the studies neglected the effects of uncertainties associated with the system, wherein the design approaches have been entirely on deterministic scale. Hence, it is deemed important to identify the complexities in the system, and in this regard, a probabilistic framework is proposed which utilizes the effects of uncertainties in the system to compute the failure probabilities of a reinforced concrete (RC) structural member under extreme blast loading. The structural member adopted here is a three-dimensional (3-D) RC wall panel, which is modeled considering material and geometric nonlinearity, and the subsequent analysis is carried out under surface-burst and free airburst scenarios. High strain rate effect induced in the RC wall is modeled using available standard dynamic increase factors (DIFs) for concrete and steel. Uncertainty in the system is assumed in material capacity (strength), mechanical loads, and dynamic blast loads considering a certain mean and standard deviation. Responses are obtained in terms of deflection, stresses, and strains at center of the wall. Limit state of failure and the respective threshold limiting values are obtained from the United States Department of Defense manual, PDC-TR 06-08 (2008). Finally, first-order sensitivity analysis is conducted to show the extent of uncertainties in input parameters affecting the output response quantities. It is concluded that the uncertainty induced in the system has significant influence in the response of the wall panels under blast loading scenarios. Moreover, based on the sensitivity analysis performed, charge weight, standoff distance, and strength of concrete material are suggested to be crucial parameters for design of blast-resistant structures. To conclude, based on the currently considered scenario of intensity of blast, exposure type, and performance level required by the user, it is recommended to use wall panels of sizes more than 100 mm in civil structures, especially 125 mm to counter the effects of extreme blast loadings.

Equivalent SDOF Load Transformation Factors for One-Way Members Subjected to Air Blast Loading

The equivalent single-degree-of-freedom (SDOF) load transformation factor expressions of the simply supported, fixed end and simply-fixed one-way members subjected to air blast loading are derived by finite series-expansion method or finite point-fitting method. Moreover, figures are used to show the relative relationship between the load transformation factors KL and the ratio of stand-off distance to structural span (γ). The typical calculation conditions show that the load transformation factors are sensitive to the piecewise function of peak overpressure when γ is less than 0.5. The load transformation factor will be a smooth curve for peak overpressure adopting a single smooth continuous function. For the blast-resistant structural design, if the error of 3% in the elastic stage and 5% in the plastic stage can be allowed, γ = 1.0 is the demarcation point between near field blast and far field blast. In addition, if the error of 0.5% can be allowed, γ ≥ 2.0 can be treated as the far field blast. The calculation results of far field blast show that the values of KL of simply supported, simply-fixed, and fixed-end members are 0.64, 0.58, and 0.54, respectively, which means that the load transformation factor is insensitive to the selection of shape function in vibration mode function or static deflection curve function. The calculation accuracy of KL expression for simply supported beam structure in this paper has been verified through near field blast experiments. This paper provides a clear numerical definition for the distinction between near field and far field explosions. It provides qualification criteria for analyzing explosion categories in blast-resistant structural design and a reference for the selection of theoretical calculation formulas.

Blast Response of Single-Degree-of-Freedom Systems Including Fluid-Structure Interaction

AbstractThe state of the practice for the blast-resistant design of structures uses a simplified single-degree-of-freedom (SDOF) analysis and estimates the blast loads assuming reflection from an u...

Air blast TNT equivalence concept for blast-resistant design

Trinitrotoluene (TNT) equivalence is a well-known concept, which has been extensively employed by the engineering community for the blast-resistant design of structures. It is invoked to predict the blast parameters generated from detonations of other types of high explosives. However, TNT equivalence factors available in the literature usually have significant variability, which may lead to large errors in estimating the blast loads. This study discusses the air blast TNT equivalence factors of seven types of high explosives (Composition A3, Composition B, Composition C4, PBX-9404, PBX-9501, Pentolite and Tetryl) for free air and surface bursts. The authors presented a numerical approach in the previous study, which used a curve fitting method to develop the empirical formulae of TNT equivalence factors. This paper extends the previous study by applying this numerical approach to the high explosives, which were extensively discussed by the blast engineering community in the past. The empirical formulae, which depict the TNT equivalence factors for overpressure and impulse as a function of the scaled distance Z, are developed for each explosive. To demonstrate the full potential of the developed empirical formulae, the results of TNT equivalence factors are verified against data collected from different sources. Two important conclusions are drawn. Firstly, the significant variance of TNT equivalence factors in the near field (Z from 0.1m/kg1/3 to 1.1-1.7m/kg1/3) requires different values depending on the scaled distance, as a constant value is insufficient for this range. Secondly, far-field detonations (Z from 1.1-1.7m/kg1/3 to 10m/kg1/3) allow a constant value of TNT equivalence to be used for each explosive, which is independent of the scaled distance, selected blast parameter for comparison (overpressure or impulse) and burst type (free air or surface burst).

Blast resistance of steel plate shear walls designed for seismic loading

Since a blast loading or explosion can create nonlinear wave action and impact pressure on a structure, it necessary to construct a structure to resist blast loading as like other loads. In this study the nonlinear behaviour of a blast loading is simulated by calculating the pressure diagram with respect to time under the guidance of IS 4991 – 1968, code for “Criteria for Blast Resistant Design of Structures for Explosions above Ground”. The study carried out for different charge weight (100kg TNT, 200kg TNT and 400kg TNT) and standoff distances of 20metre. Nonlinear behaviour of a Blast loading to steel structures with shear plates of thickness 6 mm, 8 mm and 10 mm are modelled in ETABS and the analysis is carried out to obtain base shear, story displacement, story deformation pattern, column forces, etc.

Analysis of Blast Resistant Structure (TNT Storage Case Study)

The explosions produce extreme and unique loading on structures and can cause widespread damage to the building’s structural elements. Design of blast resistant structures provides structural integrity and acceptable levels of safety for buildings. The previous studies show that some structural systems could provide substantial increase in protection against blasts. This paper discussed the behavior of TNT loaded storage (a framed reinforced concrete (. the results of calculated pressure Using Reference (UFC)-3-340-02 [1] Equation and investigated that the average peak reflected pressure close to 5000 Psi. CSI-ETABS Software 3D model shows that the structural system of case study unsafe under 0.5 tons of TNT internal weight charge.

Ability of steel fibers to enhance the shear and flexural behavior of high-strength concrete beams subjected to blast loads

The provision of steel fibers improves many of the properties of high-strength concrete (HSC), including its tensile capacity, ductility, toughness and fragmentation resistance. These enhanced features also make high-strength fiber reinforced concrete (HSFRC) an ideal material for the blast resistant design of structures. One of the established applications of fiber-reinforced concrete is in beams, where fibers can be used to increase shear capacity and replace transverse reinforcement. While extensive research exists on the behavior of FRC and HSFRC beams under static loads, studies examining the blast behavior of such beams is scarce. Accordingly, this paper presents the results of an experimental program which studies the effect of steel fibers on the blast performance of high-strength concrete beams. As part of the study, ten HSFRC beams are tested under either static loads or simulated blast loads using a shock-tube. Test variables include the effects of fibers, fiber content, fiber type, longitudinal steel ratio and combined use of fibers and transverse reinforcement. The results show that the use of fibers in HSC beams increases blast resistance, improves control of displacements and results in superior damage tolerance. In addition, the results show that steel fibers can substitute for transverse reinforcement and prevent blast-induced shear failures. The analytical investigation shows that the use of SDOF analysis, with development of non-linear resistant functions, can be used to predict the blast response of HSFRC beams with good accuracy.

Multi-objective optimisation of steel moment frames subjected to blast

In recent decades, terrorist attacks have been increased all over the world. For this reason, the design of blast resistant structures is very crucial. On the other hand, for decades the optimum design of structures has been an interesting subject for structural engineers and researchers as it can provide cost and behavioural efficiencies. In the current research, the optimum design of steel moment frames under blast loading has been studied. Towards that end, first, a damage index is developed based on the maximum plastic strain in the members. Then, according to the damage index, a multi-objective optimisation methodology is proposed to minimise the structural weight and the damage index. The method utilises explicit nonlinear dynamic finite element analysis as the structural analysis method and NSGA-II optimisation algorithm as the optimisation technique. At the final point, based on the proposed method a framework is developed, and two numerical examples are studied. Results of this research show that the developed method is effective in achieving optimal designs with desired cost and damage.

Modeling, Simulation and Optimization of Steel Sandwich Panels under Blast Loading

Honeycomb sandwich panels are commonly preferred in structural engineering as a design element meant to protect against blast loading, and this owes primarily to the fact that they are light in weight (due to the voids present) whilst carrying high energy absorption capacities. A widespread surge in acts of terrorism, and the resultant threat posed to structures, presents structural engineers with unique challenges pertaining to the design of blast-resistant structures that are both safe and reliable. Researchers worldwide have thus taken to closely studying the effects of sudden loads effected by detonative forces on certain elements and design concepts. To this end, an emergent design concept with proven efficacy is the honeycomb sandwich panel. Due to the practical difficulties associated with the study of explosive materials and replicating blast loads, software-based modeling and simulation may be favorable as a functional and convenient alternative. To this end, this work uses the finite element package ABAQUS® to study the behavior of hexagonal and squared honeycomb steel sandwich panels under the explosive effects of different amounts of trinitrotoluene (TNT). The results of finite element modeling of a specific honeycomb configuration are initially validated by comparing them with the experimental results from literature. Several configurations including different geometrical properties of the honeycomb wall are then investigated and the results are compared. Consequently, an optimization study is conducted with an objective to reduce the plastic strain of the back plate while the wall cell thickness is taken as a variable. Finally, the effectiveness of the core shape and wall thickness is discussed and conclusions are made.

Strain rate effect on the mechanical behavior of basalt: Observations from static and dynamic tests

Basalt rock is often used as a building material and in architectural design of building by constructing thin veneer and facade. Thus, dynamic characterization of basalt rock is of utmost importance in blast resistant structural design. This paper discusses static and dynamic, compressive and tensile mechanical behavior of Deccan Basalt obtained from Deccan plateau, India. The dynamic tests have been performed at strain rates ranging from 200 to 1600/s using split Hopkinson pressure bar (SHPB) with certain modifications in a conventional setup. The present test results are compared with other available data from the literature on igneous rocks to understand the influence of loading rate on Deccan Basalt in terms of the peak failure stress, modulus of elasticity, deformation modulus, and strain energy. An empirical correlation on dynamic increase factor (DIF) for the compressive and tensile strength of Basalt is proposed by comparing present experimental results with all other available data from the literature on Basalt.

Progressive collapse analysis of a typical RC high-rise tower

The world has recently witnessed tremendous increase in terrorist activities. This led to the requirement of blast resistant design of structures. The progressive collapse of structures, being the most severe consequence of blast generated waves, has been the subject of several studies. Although structural engineers are developing methodologies for the mitigation of progressive collapse, there is a lack of adequate tools that can be employed for simulating and predicting the progressive collapse response of structures with acceptable confidence. An attempt has been made in this paper to develop a practical and acceptable procedure for the progressive collapse analysis of reinforced concrete (RC) framed structures. The adequacy of the procedure has been demonstrated by studying the progressive collapse behavior of a typical RC framed high-rise building in Riyadh when exposed to blast generated waves.

ENERGY ABSORPTION AND DAMAGE OF INELASTIC SDOF STRUCTURES UNDER BLAST LOADS

Important and critical structures should be designed to resist transient extreme loads such as high velocity impacts and explosions. Blast-resistant design of structures includes architectural design and structural design against explosion forces. Blast loads could be internal due to explosion of gas pipes or external due to chemical bombs and car attacks. During the last few years, Egypt witnessed terrorist bombs and car attacks on important structures. These events caused large life losses and led to severe damage and collapse of several heritage and security buildings. In this paper, the response and damage of single-degree-of-freedom (SDOF) structures to blast loads are presented. The blast load is modeled as a time-variant function with positive and negative pressure zones. Firstly, the governing nonlinear differential equation of motion for SDOF of inelastic structures under blast load is provided. Subsequently, the solution of this equation is obtained using numerical integration of the equation of motion in the MATLAB platform [1]. Finally, the definition of various energy terms dissipated by the structure and associated damage indices are given. The formulation developed is numerically demonstrated with reference to energy dissipated and damage of a simple structure modeled as a SDOF inelastic system to blast load. A new scalar index based on damage indices is proposed. These measures are of essential importance since they provide quantitative measures on damage level of the structure and necessary repair.

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...