Explosive Loading Research Articles

Time-history blast response and failure mechanism of RC columns using Lagrangian formulation

Structural behavior of RC structures under explosive loads is an emerging field of research especially RC columns since the damage of RC columns can lead to progressive collapse. Most research works investigated and concentrated on the behavior of RC columns when exposed to far-field detonations (FFD). A limited study is available on the effects of near-field detonation (NFD) and close-in detonation (CID) on the behavior of RC columns. Hence, the main purpose of the current research is to investigate the influence of different types of detonation scenarios on the dynamic behavior of RC columns. The influences of extreme loading conditions on the columns are defined by using Lagrangian analyses in LS-DYNA. Validation of the numerical model is implemented by comparing the numerical analysis results with UFC 3–340-02 Standard. It is shown that the model yields a reliable prediction of damage on all RC columns. Intensive studies are performed to evaluate the influences of various scaled distances on the dynamic behavior of the columns. The results demonstrated that when the columns are subjected to CID explosions, they undergo the maximum pressure and the columns fail due to severe impulsive regime loading. The results revealed that when the scaled distance is in the CID range, the peak blast load increases but the duration of the positive phase of the blast wave decreases resulting in higher amplitude, lower-duration shock pulse and when the scaled distance is in the FFD range, the peak blast load decreases but the duration of the positive phase blast wave increases resulting in lower amplitude, longer-duration shock pulse. Also, the results show that increasing the scaled distance in RC columns subjected to NFD and FFD detonations resulted in a further decrease in the peak deflection histories and damage degree of RC columns in comparison to CID explosions. The current investigation and the outcomes can be utilized for evaluation of the effect of an explosion on the RC columns.

Simplified calculation of airblast variability and reliability-based design load factors for spherical air burst and hemispherical surface burst explosions

There can be significant uncertainty and variability with explosive blast loading. Standards and codes of practice are underpinned by reliability-based principles, and there is little reason not to apply these to explosive blast loading. This paper develops a simplified approach where regression equations may be used to predict the probabilistic model of airblast variability and associated reliability-based design load factors (or RBDFs) for all combinations of range, explosive mass and model errors. These models are applicable to (i) hemispherical surface bursts, and (ii) spherical free-air bursts. The benefit of this simplified approach is that the equations can be easily programed into a spreadsheet, computer code or other numerical methods. There is no need for any Monte-Carlo or other probabilistic calculations. Examples then illustrate how model error, range and explosive mass uncertainty and variability affect the variability of pressure and impulse, which in turn affect the damage assessment of residential construction.

Internal Explosion Load Computation and Structural Response of Storage Tank Based on Heat-Fluid-Solid Coupling

Internal Explosion Load Computation and Structural Response of Storage Tank Based on Heat-Fluid-Solid Coupling

A new equivalent method for complex-shaped pulse loading based on saturation analysis and membrane factor method

The dynamic plastic response with large deformation of thin plates under simple pulse loading has been studied systematically over past decades by using modal analysis and transient analysis. However, it is difficult to carry out the corresponding theoretical analysis directly for the more complex-shaped loading pulse. Hence, it is highly desired to find a pulse-equivalent technique to replace the real complex-shaped pulse by a simple pulse (e.g., a rectangular pulse), which produces the same deflection as the complex-shaped loading pulse while is relatively easier to analyze. In this paper, taking the fully clamped square plate under exponentially decaying (ED) pulse as a major example, for which the complete solution is given in [37], as obtained by the combination of Membrane Factor Method (MFM) and Saturation Analysis (SA). With the formulae on the saturated deflection and saturated impulse resulted from this solution, we are able to not only compare the Saturation Equivalent Method (S-EM) with the classical Youngdahl Equivalent Method (Y-EM), but also propose a new equivalent method, named as Progressive Equivalent Method (P-EM). By adopting a multi-step equivalency to gradually approach the saturated deflection, P-EM is capable of handling various complex-shaped loading pulses while Youngdahl empirical formula is no longer in need. The procedure of applying P-EM is also demonstrated by an example of handling complex-shaped pulses produced by constrained explosion loading, which contain multiple peaks. An extensive comparison concludes that in case of complex-shaped pulse loading, the innovative P-EM shows clear advantages over Y-EM and S-EM, and provides great convenience for engineering assessment and design.

The Dynamic Caustics Test on the Growth Law of Fractures in Tunnel Surrounding under Explosive Load

The Dynamic Caustics Test on the Growth Law of Fractures in Tunnel Surrounding under Explosive Load

Analiza čvrstoće konstrukcije oružja ratne mornarice

Due to the modernization of warships, it was necessary to carry out strength calculations for the newly assembled devices, for which there were no detailed technical requirements. The authors try to present and harmonize the requirements for naval military structures. The lack of experimental verification of newly built systems was indicated. Therefore the finite element method was used to determine the durability of the critical design elements. There is no explicit reference load in the literature, so the authors present a general solution to one of the worst cases. The work presents the cannon structure elements exposed to damage during the underwater explosion load, using the proposed methodology. The proposed method is sufficient to calculate individual ship cases. However, in the case of hull strength analysis, more complex algorithms should be used.

Study on vibration effect of pre-splitting crack in tunnel excavation under thermal explosion loading

The rapid development of the city has brought the traffic serious problems, the subway construction greatly alleviates the heavy traffic. Due to the limitation of geology and mechanical equipment, mining method is often used in subway construction. However, the vibration caused by blasting rock is the most obvious disaster of this method. For solving this problem, this paper, taking a metro station as a case, verified the effectiveness of the pre-splitting crack on the damping above the tunnel face by simulation. Furthermore, the article examines the effect of material of the medium, pre-splitting crack width and the number of blasting holes on the damping vibration. The results show that the increase in diameter improves the energy and vibration absorption performances of damping hole better than the decrease in the distance. In addition, damping performance in gas and liquid medium is better than that in solid medium. The results show that the particle vibration velocity in Z direction increased near the tunnel vault (within 5 m), which does not conform to the vibration attenuation law of Sadovsky's formula. This suggests that the vibration velocity at the ground measuring point is not the maximum. The pre-splitting crack interfered with the propagation of seismic wave, and its barrier greatly weakened the vibration velocity of ground measuring points. Compared with the ground of the tunnel without pre-splitting crack, the vibration velocity is reduced by about 40%. In addition, damping performance in gas and liquid medium is better than that in solid medium. Increasing the width of pre-splitting crack would not enhance the damping performance. What's more, the number of blasting holes does not affect the damping performance of the pre-splitting crack.

Research on Damage Characteristics of Brick Masonry under Explosion Load

As the main structural component of partition wall or load-bearing wall, brick masonry has been widely used in construction engineering. However, brick and mortar are all brittle materials prone to crack. Nowadays, fireworks, gas stoves, high-pressure vessels, and other military explosives may explode to damage nearby structures. Many explosion casualties had shown that the load-bearing capacity of brick masonry decreased dramatically and cracks or fragments appeared. Previous studies mainly focused on noncontact explosion in which shock wave is the main damage element. In fact, the response and damage effect of brick masonry wall under contact explosion are more complex, which attracts more attention now. In order to explore the damage characteristics of brick masonry under explosion load, a series of simulations and verification experiments are conducted. RHT and MO granular material models are introduced to describe the behaviour of brick and masonry, respectively, in simulation. The combination effect of front compressive wave and back tensile wave are main factors influencing the breakage of masonry wall. The experimental results are well in accordance with the simulation results. The front cross section dimension of crater is closely related to the radius of spherical explosive charge. A power function predictive model is developed to express the relationship between the radius of hole and the radius of explosive. Furthermore, with increasing the quantity of explosive charge, the number and ejection velocity of fragments are all increased. The relationship between maximum ejection velocity and the quantity of explosive also can be expressed as a power function model.

Damage assessment of prefabricated prestressed channel slab under plane charge blast

The study of the mechanical properties of prestressed concrete channel slabs under different plane charge air blasts for applications in civil defense engineering is significant. For this reason, similar simulation tests were conducted on the anti-explosive performance of three 1:3 scale prestressed concrete channel slabs under 9 times plane charge air blast. The positive duration was more than 260 ms to simulate the uniform distribution load of a strong blast air shock wave on the prestressed concrete channel slab. The results showed that the designed prestressed concrete channel slab had good displacement ductility without brittle destruction, which significantly reduced the damage of the blasting impact on the structure. The channel slab could resist an air shock load of 0.467 MPa without damage. On the other hand, the positive duration was not only related to the quality of the overlying soil but also related to the air shock wave overpressure design value. The channel plate is regarded as a rigid-plastic component to calculate its plastic dynamic response under explosive load. In addition, the reliability of the theoretical calculation results and ABAQUS software simulation were verified by experimental data, which provided a feasible analytical method for calculation and simulation research in civil air defense engineering.

Research advance of damage load of surface ship cabin explosion

<p indent=0mm>With the enhancement of the ship’s protective structure, the development of anti-ship missiles with significant attack advantages is extremely rapid. This type of weapon can penetrate the outer deck and explode in crucial compartments, thus destroying the functional systems of the ship. Therefore, it is very important to master the load characteristics of anti-ship missile cabin explosion for the design of ship’s protective structure. This paper systematically summarizes the research progress of the formation and characteristics of three types of explosion loads after the anti-ship missile explodes in the cabin. Starting from the types of explosive loads in the cabin-shock wave, quasi-static pressure and high-speed fragment group, we systematically review their formation mechanism, calculation formula and structural damage modes, and finally propose the research direction of cabin blast and the problems to be further studied.

Synergistic response of steel columns to explosive thermal and long duration blast loading

This paper investigates the response of steel columns to combined pre-cursor thermal and long duration blast loads. Blast waves are the primary damage mechanism from explosive events. However, explosive events also emit thermal loads. Depending upon the explosive size and standoff distance, the effective thermal load can reach a structure prior to the arrival of the blast. An effective thermal load can damage steel structures such that total damage from the combined thermal and blast load is different to, or greater than the blast load alone. There is limited research to date investigating the synergistic response of steel structures to explosive thermal and blast loading. This paper specifically focuses on the numerical and computational methods appropriate to predict the response of steel columns subject to focused thermal and long duration blast loads (positive pressure phase exceeding 100 ms). Results from a substantive study are presented, showing a synergistic response within a sensitivity envelope of load cases. Computational methods are verified with a novel series of explosive fireball trials and a series of combined thermal, compression and long duration blast trials.

Dynamic response and safety assessment of buried gas pipe subjected to ground surface explosion

Dynamic response of buried gas pipe subjected to the ground explosion is an important issue for the safety assessment of pipe. In this paper, the explosion tests of the full-scale model and 3D numerical models were employed to evaluate the dynamic response characteristics of the ground particles and the pipe. Meanwhile, parametric analysis was conducted to discuss the effects of different types of parameters for explosion source and pipe on the buried gas pipe's peak particle stress (PPS). Meanwhile, combined with the dynamic stress yield criterion of the pipe, the control standard of explosive charge under the action of the ground explosive load is obtained to prevent the damage of pipelines in different buried depths. The results showed that during third-party blasting operations, the internal pressure of the pipe should be reduced to better protect the pipe from damage, and attention should be paid to the velocity in the Y-direction of the pipe and the ground surface. Meanwhile, more attention should be paid to the safety protection of the buried pipe close to the interface between rock and soil.

Analysis on the blast resistance of steel concrete composite slab

Steel concrete steel composite slab is a new type of composite structure. It has the characteristics of high shear strength, high ductility and strong energy consumption compared with the traditional reinforced concrete slab. The new type composite slab has been widely used in nuclear reactor containment, offshore platform and oil storage tank. Two scaled reinforced concrete slabs (RCS) and steel-concrete-steel (SCS) composite slabs were designed and manufactured, and the experimental study was carried out under the contact explosion load. The anti-blast performance of different slabs was analyzed by damage analysis and displacement. Based on ANSYS/LS-DYNA nonlinear finite element program, the damage modes and the maximum deflection of the mid-span of the steel-concrete composite slab are numerically investigated, and the numerical damage modes and maximum deflection of the steel-concrete composite slabs are compared with the test results of the components, which verifies the accuracy and applicability of the finite element analysis model. In this study, the influences of parameters, such as explosive quantity, concrete strength and steel plate thickness on the anti-blast performance of steel-concrete composite plate are numerically analyzed by parametric analysis. Then, the prediction formula of mid-span deflection of SCS slab is proposed by using the method of multi parameter regression analysis. The results show that the plastic damage of the structure can be reduced by increasing the strength of concrete, and the maximum deflection of SCS can be effectively reduced by increasing the thickness of steel plate. It is indicated that the SCS maintains good integrity and owns the ability to continue to carry load compared with the RCS. Finally, the fitting formula can well predict the relationship between the mid span deflection of SCS plate and the charge amount and the thickness of steel plate.

LARGE DEFORMATION BEHAVIOUR OF THIN MILD STEEL RECTANGULAR PLATES SUBJECTED TO UNDERWATER EXPLOSION LOADING UNDER AIR AND WATER BACKED CONDITIONS

Marine vehicles in their operation as military vehicle are susceptible for underwater explosion from mines, torpedo etc. The damage inflicted on such structures made of ductile materials can be large deformation, tearing, rupture etc. It is imperative to design such structures for withstanding explosive loads. The damages inflicted will be mostly localized between the frames and stiffener, which can be considered as plate clamped at the edges. Hence, an attempt has been made in this paper to study the localized deformation of thin mild steel plates subjected to underwater explosion through limited explosion bulge test using small explosives. The experiments exhibited Mode I: large deformation, Mode IIa: Partial tensile tearing, Mode IIc: central rupture and Counter Intuitive Behaviour (CIB). The problem is simulated numerically using LS DYNA nonlinear finite element code considering fluid – structure interaction and the results compared with experiments. Based on the confidence gained for the air backed conditions, the analysis is extended to water backed (fully filled, 75% filled, 50 % filled) conditions and results obtained for the large deformation behaviour for various conditions are presented. The results indicate that the large deformation behaviour considerably reduces the central permanent deformation under water backed conditions compared to air backed conditions due to the fact that part of shock wave gets transmitted to the water medium behind the plate in water backed conditions.

Experimental study of the shock response of a medium floating shock platform subject to an underwater explosion

<p indent="0mm">A medium floating shock platform was selected as an object, and the shock response affected by underwater explosions was investigated using theoretical and experimental methods. First, the shock response of the platform was tested using experimental methods, such as underwater explosive load, platform shock environment, and structure damage stress. Experimental results were obtained using experimental methods. Second, based on the test results, the platform characteristics were analyzed using theoretical methods, such as the damage status of the platform structure, the environmental acceleration distribution, and the vibration reduction effect of the cushion system. Signification phenomena were obtained by analyzing experimental data and comparing it with the theoretical results. The damage level of the platform belongs to the gradation of light. The maximum shock wave, acceleration, and structural stress to the front-explosion surface are more prominent than those to the back-explosion surface. The maximum structural stress is at the bottom center of the platform. Platform equipment has perfect cushioning effects. Damping efficiency is more than 95%. The results show that the standard strength of the floating shock platform is sufficient, and the mitigation effects of the cushioning system are very effective. The theoretical analysis results are based on simulation calculations in determining the damage level of the platform.

Numerical and Experimental Approach for Failure Analysis of Soil Subjected to Surface Explosion Loading

Controlling the hazards to facilities caused by detonation waves is a high priority in engineering design. To protect an underground facility, soil can reduce the destructive effects of detonation waves. Soil dynamic characteristics and the area of the destructive zone are affected by shock wave energy. The material at ground zero is impacted by high-intensity stress and forms a crater. To ensure the safety of the facility, the protective soil layers must be sufficiently thick. Therefore, the purpose of this study was to analyze the destructive effects that caused the deformation and destruction of an external protective soil layer. The results of the explosion experiments and the numerical simulation analysis were compared to explore the dynamic characteristics of the soil affected by the shock wave and the crater effects of on-ground explosions. The analysis model adopted an 8-node hexahedral element to create a three-dimensional solid structure model of the fluid-solid interaction. The material failure analysis demonstrated that the detonation wave destabilized the interior of the soil body, and the nearby high-intensity stress was the key factor for material failure. The results can serve as a reference for the design of soil-covering layers that provide explosion hazard control.

Introducing a New Relation for Calculating the Explosion Wave Decay Coefficient

Today, due to the increase in terrorist attacks and the need to protect structures and infrastructure against these threats, especially explosive threats, the issue of analyzing the response of structures against these loads is one of the topics of the day. One of the important parameters in analyzing the response of structures is the nature and mode of the impact of the explosive load. This can be seen in the relation presented for explosive pressure in theoretical analyzes. According to the Friedlander relation, the blast pressure decreases exponentially over time, and various relations are proposed to calculate the decay coefficient of the exponential function (such as the Kinney-Graham method, the Ismail-Murray method, the Karlos- Solomosand method, etc). This coefficient indicates how the slope rate of the explosion wave time pressure graph decreases. In this paper, by examining other existing methods for calculating the decay parameter, a new relationship for the explosion pressure reduction parameter in the near and far range is presented; A comparison is also made between the relationship observed in this study and other relationships presented for the blast wave decay coefficient. The results showed that the decay parameter presented in this study with high accuracy can calculate the actual explosion pressure and this leads to a better analysis of structures against explosive threats. In this research, the high accuracy of the calculated relationships for the decay coefficient has been investigated in three ways: A) Based on the regression coefficient of fitted graphs, the value of R2 is close to one; B) by the comparison between the values of the calculated decay coefficient with other existing relations; C) Based on the actual blast pressure calculated in two numerical examples.

A review on internal blast damage effects of multi-box type structures

The damage mechanisms of structures under internal blast are important for the prediction and evaluation of damage effects of conventional weapons and the design of anti-explosion structures of buildings and ships. The researches status and existing problems are discussed in this paper, based on the following four aspects as the internal explosion loads on structures, the plastic responses of structures to internal explosion loads, the damage modes of box-wall structures under internal explosion loads, and the damage modes and distribution of multi-box structures under internal explosion loads. With respect to an internal blast load, it is recognized that the blast model can be divided into dynamic high-pressure stage and quasi-static pressure stage. The former is formed by the initial shock wave and reflection wave while the latter is mainly composed of expansion of detonation gas and chemical energy released by explosion. In regard to the plastic response of the structure under the internal blast load, the studies have shown that quasi-static pressure plays an important role in the response process. With respect to the damage mode of the internal blast loaded structure, the damage mode is greatly affected by the pressure relief mode and pressure relief speed, studies on the damage modes of the beam and plate were introduced. As regards the damage mode and distribution of multi-box structures under the internal blast load, the internal explosion damage of the metal box structure of ships was mainly introduced. Most of the current researches focus on the damage features and there is rarely systematic understanding and analysis for the damagemechanisms. Through the review of the research on the damage and damage of the structures under the internal blast load, suggestions are provided for further researches on: (1) the models to describe the internal explosion loads on more complex structures and the corresponding damage effects; (2) the mechanisms of dynamic response of the box walls to internal blast load; (3) the coupling effect of multi-box structures with internal explosion waves and detonation products; (4) the methods to quickly and accurately predict the damage mode, damage range and damage degree of structures under internal explosion loads.

Application of the Sub-Sea Analysis (SSA) capability in numerical simulation of underwater explosion

In order to solve the problem that LS-DYNA fluid-solid coupling algorithm is not suitable for remote underwater explosion simulation and improve calculation efficiency, the numerical simulation of remote underwater explosion is carried out for the subsea analysis function in LS-DYNA. The dynamic response process of ship hull girder under underwater explosive load is analyzed by comparing it with the general software AUTODYN numerical simulation. The method reflects the loading process of underwater explosion load on structure to a certain extent. The calculation speed is fast, but the accuracy is not high and the error of bubble pulsation process is large.

Resistance of all-metallic honeycomb sandwich structures to underwater explosion shock

All-metallic honeycomb sandwich structure is a new kind of ship protection structure, which has a broad application prospect in the field of ship protection. However, there is not enough research on the dynamic response of honeycomb sandwich structures under the actual underwater explosion load. The dynamic behavior and protective performance of honeycomb sandwich structures subjected to underwater explosion load were investigated, both experimentally and numerically in this paper. A backplane stiffened honeycomb sandwich structure and the corresponding buoyant box were designed and fabricated for the subsequent experimental study in a large open water pool. The structural response was numerically simulated using the coupled acoustic-structural approach (integrated in commercial FE code ABAQUS/Explicit). The numerical simulation results are in good agreement with the experimental measurements. Then, the deformation process and energy absorption characteristics of the honeycomb sandwich structure subjected to underwater explosion load were investigated. The effects of the load parameter (impact factor) and two geometric parameters (i.e., facesheet thickness ratio and core relative density) on the dynamic response of the sandwich structure were analyzed. Finally, the Pareto optimal designs with minimize value of non-dimensional areal density and minimize value of non-dimensional maximum deformation of the central point on back facesheet were obtained using the NSGA-Ⅱ algorithm. The results show that with the increase of impact factor, the overall deformation of the structure increases significantly. The honeycomb core is the main energy absorbing substructure during this process, and its energy absorption ratio gradually decreases. With the increase of either face sheet thickness ratio or core relative density, the deformation of the structure first decreases and then increases, accompanied by changes in deformation modes. The influence of core relative density is more significant. The optimized structures obtained from multi-objective optimal design effectively reduce the areal density and the maximum deformation, which can be used as a reference for the future design of honeycomb sandwich structures.