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In this study, the characteristics of static bending and free and forced vibration of double-layer auxetic functionally graded porous (FGP) sandwich plates with shear connectors under blast load are explored comprehensively, where the structure of the plate comprises two layers joined by shear connectors. Each layer comprises auxetic FGM sandwich material, containing a core component made of auxetic honeycomb with a negative Poisson's ratio, while the upper and bottom two components are made from FGP materials. The whole plate is supported by a two-parameter Winkler-Pasternak elastic foundation. The key innovation of the proposed theory is that the transverse shear stresses are zero at the two free surfaces of each layer. In contrast to previous first-order shear deformation theories, no shear correction factor is required. To solve the plate issue when the boundary condition was entirely supported, Navier's exact solution was devised. On the other hand, in order to address the plate behavior in the event that the boundary condition was altered in any way, a plate element with nine nodes was used. Besides, to determine whether or not these results are accurate, a complete comparison approach that makes use of reliable claims has been used. The problem model's special case situations are used in order to accomplish this goal. When the object being developed is exposed to explosive loads, the findings that were derived from this research have the potential to be used to the construction of both military and civil works. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear transient dynamic response of functionally graded material (FGM) sandwich doubly curved shell with homogenous isotropic material core and functionally graded face sheet is analyzed using a new displacement field on the basis of Reddy's third-order shear theory for the first time. The equivalent material properties for the FGM face sheet are assumed to obey the rule of simple power law function in the thickness direction. Based on Reddy's theory of higher shear deformation, a new displacement field is developed by introducing the secant function into transverse displacement. Four coupled nonlinear differential equations are obtained by applying Hamilton's principle and Galerkin method. It is assumed that the FGM sandwich doubly curved shell is subjected to step loading, air-blast loading, triangular loading, and sinusoidal loading, respectively. On the basis of double-precision variablecoefficient ordinary differential equation solver, a new program code in FORTRAN software is developed to solve the nonlinear transient dynamics of the system. The influences of core thickness, volume fraction, core-to-face sheet thickness ratio, width-to-thickness ratio and blast type on the transient response of the shell are discussed in detail through numerical simulation. [ABSTRACT FROM AUTHOR]

As the threat of global terrorism increases a demand for reinforced concrete structures as a physical protection also become important. The protective structures are to withstand sudden occurrence of dynamic loads like terrorist impact and blast attacks as well as vehicle and industrial accidents. In order to resist such an expected loading, the HPFRCC (High Performance Fiber Reinforced Cementitious Composite) materials may take an appropriate role by its increased fracture energy absorbing capacity. The slab member was 100mm thick and 2000mm squared SIFCON (Slurry Infiltrated Concrete) based HPFRCC and the outer surface was wrapped basalt fiber sheet. By wrapping the basalt, the specimen may attain more confining effect and the final HPFRCC is named as KNU HPFRCC. The SIFCON has about 80MPa compressive strength with steel fiber volume fraction of 5%. The used steel fibers were 60mm long with 80 aspect ratio and its tensile strength was 1100MPa. The slurry composed of ordinary Portland cement, water, fine sand and silica fume. A field blast test was performed with a HPFRCC slab against 100kgf TNT and stand-off distance of 5m. The study investigates the behavior of KNU HPFRCC. This study investigates the performance of KNU HPFRCC in terms of the field explosion blast load test. Figure 1 shows KNU HPFRCC slab specimen after the blast load test. [ABSTRACT FROM AUTHOR]

With the increase in terrorist attacks in recent years, the effects of explosions on building become highly topical. In this regard, the paper deals with the analysis of blast loaded steel structures. When a blast loaded structure is analysed, as known, two major design issues and scientific challenges have to be approached and solved. The first issue derives from the analysis and description of the input dynamic load (time-pressure wave), being dependent on the type of explosion and explosive, while the second issue is related to the analysis of the actual dynamic response of the structure under impact. As such, real field blast tests using the so called ANFO explosives are first presented. The examined constructional system consists of steel rolled beams with two different type of cross sections (HEB100 and IPE120). The actual experimental observations are then assessed and compared with both SDOF and FE models carried out in ABAQUS. In doing so, the actual shape (i.e. decaying path for the pressure load) of the experimental blast wave is used, together with two further approximations for its description. The comparative calculations are then proposed for selected control points, in terms of mechanical and kinematic quantities (i.e. displacements, accelerations and strains). A critical discussion of the so collected comparative results is hence proposed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Various critical equipments are used in nuclear, defence and aerospace industries. These equipments which are used in these industries need to be strong and light in weight. Steel, aluminium and magnesium are widely used as structural material in these equipments. With increase in global terrorism it is important that these equipments are safe under blast. Hence, it is imperative to study the behaviour of these plates when subjected to blast loading. Explicit finite element technique using Abaqus @ is used to study the effect of blast load on these plates. Elastic plastic model is used for the materials and Conwep model is used to model the blast load. Numerical simulations are carried out for monolithic plates and layered plates of different materials of equivalent weight. Various combinations of plates for equivalent weight are also studied. The paper discusses the performance of these monolithic and layered plates under blast load. [ABSTRACT FROM AUTHOR]

Nonlinear response of laminated composite plates and cylindrical panels subjected to a parabolically distributed blast load is studied here using a shear deformable finite element method. The nonlinear finite element equations of motion are solved in the time domain by an energy and momentum conserving time integration technique. The state-of-stress inside the laminated panels is calculated at each time-step to predict the occurrence of damage using Tsai-Wu quadratic failure criterion. The effects of span-to-thickness ratio, radius-to-span ratio and peak pressure on the nonlinear dynamic response of laminated composite plates and curved panels are investigated. [ABSTRACT FROM AUTHOR]

The utilization of explosives was originally intended for the benefit of mining and civil construction. However, over the years, the use of explosives is changing as the main weapon in the warfare against the opponent with advanced technology. The objective of designing structure that will resist blast impact load is not only to prevent excessive penetration, but also to prevent severe injury or fatality of the personnel inside a military vehicle. Small penetration is not always safe for military personnel. Therefore, a new term of blastworthiness is introduced as a design criteria for military vehicles. This research works deal with parametric studies on plate structures with various shapes and stiffened panel constructions. The plate was subjected to a blast load which varies in magnitude and distance from the blast source. The objective of this research is to find the relationship between the structural response and the variation of the explosion distance, explosion magnitude, configuration of stiffener of panel and curvature of the panel. Numerical analysis was performed by using non-linear finite element simulation. Blast impact was modelled as a concentrated blast load. The variation of the distance of the explosion, the magnitude of the explosion, the stiffener of the panel and the curvature of the panel strongly influenced the character of the structure receiving load explosion. Variations of these parameters provided some response trends on the penetration, velocity, and acceleration that will influence the safety level of the structure when it's applied to an armour vehicle. [ABSTRACT FROM AUTHOR]

When considering human activity nowadays one can meet the blast load overpressure caused by different actions. From the point of view of people and building security one of the main destroying factor is the air shock wave. Rational estimating of its results should be preceded with knowledge of complex wave field distribution in time and space. As a result one can estimate the blast load distribution in time. In considered conditions, the values of blast load are estimating using the empirical functions of overpressure distribution in time ( Δp(t) ). The Δp(t) functions are monotonic and are the approximation of reality. The distributions of these functions are often linearized due to simplifying of estimating the blast reaction of elements. The article presents a method of numerical analysis of the phenomenon of the air shock wave propagation. The main scope of this paper is getting the ability to make more realistic the Δp(t) functions. An explicit own solution using Finite Volume Method was used. This method considers changes in energy due to heat transfer with conservation of linear heat transfer. For validation, the results of numerical analysis were compared with the literature reports. Values of impulse, pressure, and its duration were studied. [ABSTRACT FROM AUTHOR]

Retrofitting technology and high performance construction material are now widely investigated so as to increase structural ductility and robustness under extreme loading conditions. In the present study, some recent developments in structural protection against blast loads are compiled. Metallic foam materials with varying foam density and gradient are used in the cladding design, their energy absorbing capacities and stress-strain relationships are studied based on uniaxial compression tests. These foam material are used to cast sacrificial claddings on the concrete slabs in the field blast tests. Damage and structural deformation are measured to check the effectiveness of the claddings. Besides sacrificial foam cladding, concrete material with new reinforcement scheme including steel wire mesh and micro steel fiber is developed, and the static test results indicates the excellent ductility and crack control ability of this novel design. In the field blast tests, concrete slabs with different steel wire mesh reinforcement are exposed to varying blast loads. The effectiveness of the slab reinforcing design is discussed based on field performance. [ABSTRACT FROM AUTHOR]

Ongoing terrorist attacks on many structures around the world have increased the importance of analysis of structures under blast loading. Despite the progress made in this area, there is a need to better understand the structural performance of framed concrete structures under severe loading before, inevitably, adopting any mitigation measures. Most of the structures that are damaged by bombs or impact loading are not initially designed to resist blast loads. The severe vulnerability of these structures has led to ongoing development of new provisions and guidelines of effective techniques to mitigate risks associated with explosions. In this research, detailed finite element analyses were performed using ABAQUS to assess the structural performance of reinforced concrete frames under blast loading. A model of two dimensional, 4-story reinforced concrete frame was selected for the study. The response of the structural model under the simulated blast loads is presented, along with two alternative designs as a precursor to provide mitigation guidelines in the future. Results showed that changing the design of the external columns improved the response, especially using the concrete filled steel tube section. [ABSTRACT FROM AUTHOR]

In this study, the nonlinear dynamic response of basalt/nickel FGM composite plates has been investigated under blast load. Homogenous Laminated Model (HLM) and Power-Law Model (PLM) are used to model the basalt/nickel FGM composite plates. von Kármán large deflection theory of thin plates are considered for the geometric nonlinearity effects. The equations of motion for the plate are derived by the use of the virtual work principle. Approximate solutions are assumed for the space domain and substituted into the equations of motion. Then the Galerkin Method is used to obtain the nonlinear differential equations in the time domain. The Finite Difference method is applied to solve the system of coupled nonlinear equations. The effects of two different approximations in order to model the basalt/nickel FGM composite plates have been investigated and the results are discussed. [ABSTRACT FROM AUTHOR]

Energy absorbing materials can be used as a part of building structure to enhance its blast resistance, with positive impact on the safety of citizens. In the presented study, the new energy absorber based on expanded glass grains was subjected to the high strain rate loading using the Split Hopkinson pressure bar apparatus (SHPB) and to the blast load as a part of the sandwich structure. The influence of the binder amount on the attenuating properties of the material was evaluated. The dynamic response of 6 rectangular sandwich panel constructions (with different core designs) under blast loading was investigated. The objectives were to analyse the panels in terms of deformation and blast resistance and to determine the effect of different core set-ups on blast resistance enhancement of the entire structure. 5 types of core configurations, with almost identical areal density, were prepared and subjected to the blast wave generated by the detonation of 100g of TNT equivalent explosive from the 100 mm distance. Overall blast resistance of the panel was determined using the certified methodology M-T0-B VTÚO 10/09 based on evaluation of the tension strain curves recorded by strain gages fixed at the back steel plate of the sandwich. The image analysis was used to quantify the damage of the concrete slabs. The best results were achieved in the case of stepwise graded core with decreasing grain size from the blast load epicentre. [ABSTRACT FROM AUTHOR]

To study the internal blast load, a lot of small scale internal blast experiments have been conducted. For those experiments, the influence of explosive density generally was not taken into account while it was simple to have slight density differences in application. To analyze the influence of explosive density on small scale internal blast experiments, the finite element code LS-DYNA was employed and the numerical model was established. The numerical model was validated against published experimental data and the result shows a good agreement. We found that that both the peak overpressure and impulse increase with the density of charge. Empirical equations were fitted using the calculation results to evaluate the influence of explosive density on the peak overpressures and impulses. [ABSTRACT FROM AUTHOR]

Abstract: The flexural response and failure of reinforced concrete rectangular slabs subjected to blast loading are investigated based on the rigid-plastic modelling. The effects of orthotropic reinforcement and asymmetric support bending restraints are incorporated to account for structural configurations and detailing. Two schemes of failure pattern are introduced and features of dynamic response under typical blast loading are outlined. Numerical studies are carried out and the results obtained from the present model and explicit finite element simulations are compared. It is shown that the proposed analysis is capable of capturing the essential features of dynamic response of reinforced concrete slabs and provides a simple and efficient means for blast design and assessment of concrete slabs. [Copyright &y& Elsevier]

Abstract: The response of structural concrete elements under extremely short duration dynamic loads is of great concern nowadays. The most prevailing method to this problem is based on SDOF simplification. It is well known that the SDOF model can reliably predict the overall structural component response if the response follows predominantly a predefined damage mode such as shear or flexural mode. However, it cannot reliably predict localized failure of structures. Moreover, reliable deflection shape and damage criterion, which are critical for developing the equivalent SDOF model, are difficult to define. Therefore, although most design and analysis are still based on SDOF approach, more and more analyses are conducted with detailed Finite Element (FE) modelling. However, due to the short time duration as well as the huge loading magnitude, it is extremely difficult and time consuming to perform FE structural response analysis to blast loads, even with modern computer power. In this paper, a numerical approach, which substantially reduces the modelling and computational effort in analysing structural responses to blast load, is presented. Based on the short duration of blast load, the structural response is divided into two parts: forced vibration phase and free vibration phase. In the proposed method, the response during the forced vibration phase is approximately solved using the SDOF approach. Using the estimated response quantities at the end of the forced vibration phase as the initial conditions, a detail FE model in LS-DYNA is established and free vibration response is solved. This approach, while yielding reasonably accurate response calculations, substantially reduces the modelling and computational effort. To demonstrate the method, a reinforced concrete beam is analysed using both the conventional detailed FE modelling and the proposed approach. Comparisons of the numerical results from the two methods demonstrate the reliability of the proposed method. Compared to the detailed FE modelling, the proposed method requires only a rather coarse FE mesh, and can use a larger integration time step for free vibration calculations. Therefore, it requires less than 5% of the computational time to predict the structural responses as compared to the detailed FE modelling approach. [Copyright &y& Elsevier]

Even though fiber reinforced polymer (FRP) has been widely used as a retrofitting material, the FRP behavior and effect in FRP retrofitted structure under blast loading, impulsive loading with instantaneous time duration, has not been accurately examined. The past studies have focused on the performance of FRP retrofitted structures by making simplifications in modeling, without incorporating accurate failure mechanisms of FRP. Therefore, it is critical to establish an analytical model that can properly consider the specific features of FRP material in evaluating the response of retrofitted concrete structures under blast loading. In this study, debonding failure analysis technique for FRP retrofitted concrete structure under blast loading is suggested by considering FRP material characteristics and debonding failure mechanisms as well as rate dependent failure mechanism based on a blast resisting design concept. In addition, blast simulation of FRP retrofitted RC panel is performed to validate the proposed model and analysis method. For validation of the proposed model and analysis method, the reported experimental results are compared with the debonding failure analysis results. From the comparative verification, it is confirmed that the proposed analytical model considering debonding failure of FRP is able to reasonably predict the behavior of FRP retrofitted concrete panel under blast loading. [ABSTRACT FROM AUTHOR]

Damage assessment for buried structures against an internal blast is conducted by considering the soil-structure interaction. The structural element under analysis is assumed to be rigid-plastic and simply-supported at both ends. Shear failure, bending failure and combined failure modes are included based on five possible transverse velocity profiles. The maximum deflections with respect to shear and bending failure are derived respectively by employing proper failure criteria of the structural element. Pressure-Impulse diagrams to assess damage of the buried structures are subsequently developed. Comparisons have been done to evaluate the influences of the soil-structure interaction and the shear-to-bending strength ratio of the structural element. A case study for a buried reinforced concrete structure has been conducted to show the applicability of the proposed damage assessment method. [ABSTRACT FROM AUTHOR]

The characteristic response of a structure to blast load may be divided into two distinctive phases, namely the direct blast response during which the shock wave effect and localized damage take place, and the post-blast phase whereby progressive collapse may occur. A reliable post-blast analysis depends on a sound understanding of the direct blast effect. Because of the complex loading environment and the stress wave effects, the analysis on the direct effect often necessitates a high fidelity numerical model with coupled fluid (air) and solid subdomains. In such a modelling framework, an appropriate representation of the blast load and the high nonlinearity of the material response is a key to a reliable outcome. This paper presents a series of calibration study on these two important modelling considerations in a coupled Eulerian-Lagrangian framework using a hydrocode. The calibration of the simulated blast load is carried out for both free air and internal explosions. The simulation of the extreme dynamic response of concrete components is achieved using an advanced concrete damage model in conjunction with an element erosion scheme. Validation simulations are conducted for two representative scenarios; one involves a concrete slab under internal blast, and the other with a RC column under air blast, with a particular focus on the simulation sensitivity to the mesh size and the erosion criterion. [ABSTRACT FROM AUTHOR]

In this paper the study of a reinforced concrete wall used as protection against accidental explosions in the petrochemical industry is presented. Many alternatives of accidental scenarios and sizes of the wall are analyzed and discussed. Two main types of events are considered, both related to vessel bursts: Pressure vessel bursts and BLEVE. The liberated energy from the explosion was calculated following procedures firmly established in the practice and the effects over the structures and the reinforced concrete wall were calculated by using a CFD tool. The results obtained show that the designed wall reduces the values of the peak overpressure and impulse and, as a result, the damage levels to be expected. It was also proved that a reinforced concrete wall can withstand the blast load for the considered events and levels of pressure and impulse, with minor damage and protect the buildings. [ABSTRACT FROM AUTHOR]

Local failure of a primary structural component induced by direct air-blast loading may be itself a critical damage and lead to the partial or full collapse of the building. As an extensive research to mitigate blast-induced hazards in steel frame structure, a state-of-art analytical approach or high-fidelity computational nonlinear continuum modeling using computational fluid dynamics was described in this paper. The capability of the approach to produce reasonable blast pressures on a steel wide-flange section column was first evaluated. Parametric studies were conducted to observe the effects of section sizes and boundary conditions on behavior and failure of columns in steel frame structures. This study shows that the analytical approach is reasonable and effective to understand the nature of blast wave and complex interaction between blast loading and steel column behavior. [ABSTRACT FROM AUTHOR]