Blast Loading Scenarios Research Articles

Reliability-Based Design Load Factors for Explosive Blast Loading

AbstractReliability-based design allows the decision maker to select the level of reliability for a specific blast loading scenario and key to this is an understanding of airblast uncertainty. Hence, explosive field trials have been conducted in Australia that measured the variability of free-field blast loading caused by military standard plastic explosives. The results have revealed a high level of variability of peak incident pressure, impulse, and time of positive phase duration for repeatable tests where variability would be expected to be a minimum. The accuracy of predictive blast load models (model error) was also assessed. A probabilistic blast load computer model is revised to capture these observed variabilities. The effect of a 20% mass-increase safety factor typically applied to explosive mass on the probability of exceeding a design blast load is assessed. Reliability-based load factors are calculated where the nominal load is multiplied by the load factor to ensure that the actual load is e...

Numerical Investigation of the Response of Protective Barrier under Blast Loading

Non-composite steel-concrete-steel panels develop high load-carrying capacity through the tensile membrane resistance of the steel faceplates at large displacement. The response of a full-scale barrier structure composed of the non-composite SCS panels and steel posts under various blast loading scenarios was investigated using non-linear finite element software LS-Dyna. The simulation results showed that the barrier was able to withstand very large blast energy. It can be concluded that non-composite SCS panels can provide an attractive solution to expedite construction of high-performance protective barriers to resist extreme blast loadings.

Helmet liner evaluation to mitigate head response from primary blast exposure

Head injury resulting from blast loading, including mild traumatic brain injury, has been identified as an important blast-related injury in modern conflict zones. A study was undertaken to investigate potential protective ballistic helmet liner materials to mitigate primary blast injury using a detailed sagittal plane head finite element model, developed and validated against previous studies of head kinematics resulting from blast exposure. Five measures reflecting the potential for brain injury that were investigated included intracranial pressure, brain tissue strain, head acceleration (linear and rotational) and the head injury criterion. In simulations, these measures provided consistent predictions for typical blast loading scenarios. Considering mitigation, various characteristics of foam material response were investigated and a factor analysis was performed which showed that the four most significant were the interaction effects between modulus and hysteretic response, stress–strain response, damping factor and density. Candidate materials were then identified using the predicted optimal material values. Polymeric foam was found to meet the density and modulus requirements; however, for all significant parameters, higher strength foams, such as aluminum foam, were found to provide the highest reduction in the potential for injury when compared against the unprotected head.

Structural Response to Blast Loading: The Effects of Corrosion on Reinforced Concrete Structures

Structural blast design has become a necessary part of the design with increasing terrorist attacks. Terrorist attacks are not the one to make the structures important against blast loading where other explosions such as high gas explosions also take an important place in structural safety. The main objective of this study was to verify the structural performance levels under the impact of different blast loading scenarios. The blast loads were represented by using triangular pulse for single degree of freedom system. The effect of blast load on both corroded and uncorroded reinforced concrete buildings was examined for different explosion distances. Modified plastic hinge properties were used to ensure the effects of corrosion. The results indicated that explosion distance and concrete strength were key parameters to define the performance of the structures against blast loading.

Numerical and experimental blast response characterization of sandwich composite structural panels

Experimental blast response and quasi-static material property data were obtained for E-glass and carbon face skin sandwich composite panels with balsa, polyvinyl chloride foam, and TYCOR® cores. The pressure versus impulse ( P–I) curve methodology enabled the generation of a database of performance envelopes for these sandwich composite panel configurations under different blast loading scenarios. The strength versus deformation properties of various undamaged sandwich composite panels are established numerically and idealized for single-degree-of-freedom modeling. Results show good correspondence between model predictions and experimental results for performance evaluation of the various sandwich composite structural panel configurations that were investigated.

A Two-Step Numerical Method for Efficient Analysis of Structural Response to Blast Load

Even with modern computer power, detailed numerical modeling and simulation of structure response to blast loads are still extremely expensive and sometimes prohibitive because it is very time consuming and requires huge computer memory. Often compromise has to be made between simulation efficiency and simulation accuracy. A lot of research efforts have been spent on improving the computational efficiency. Most of these researches concentrate on simplifying the structures, such as simplifying a structure to an equivalent SDOF system, use smeared reinforcement steel and concrete model, use substructure approach to only model part of the structure in detail. Although these approaches under certain conditions yield reliable predictions, each of them has its associated limitations. Recently a two-step method was developed to improve the computation and modeling efficiency of structure response to blast loads. Instead of simplifying the structure, the proposed method calculates the structural responses in two steps. The first step calculates the structural responses in the loading phase and the second calculates the free vibration responses with the velocity profile of the structure at the end of the loading phase as initial conditions. Using a reinforced concrete beam as the example, it was found that the proposed method yields reliable predictions of the overall beam deflection and stress in longitudinal reinforcement bars with less than 10% computational time as compared to a detailed FE model simulation. However, the predicted stress in hoop reinforcements near the beam supports is not as good. In this paper, the method is improved by also including displacement response at the end of the forced-vibration phase as the initial conditions in the free vibration analysis. The same reinforced concrete beam is used. The results show that including the displacement initial conditions in the two-step method leads to an improved prediction of the beam responses. Parametric calculations are performed in this study by varying the blast loading amplitude and duration. Using the detailed FE model simulation results as benchmark, the prediction errors on various response quantities and savings on computational times of the proposed two-step method with respect to different blast loading scenarios are presented. The accuracy and efficiency of the proposed method in predicting structural responses and damage to blast loadings are demonstrated in this paper.

Investigation of Head Response to Blast Loading

Head injury resulting from blast loading, specifically mild traumatic brain injury, has been identified as a possible and important blast-related injury for soldiers in modern conflict zones. A study was undertaken to evaluate head response to blast loading scenarios using an explicit finite element numerical model and to comment on the potential for head injury. The blast loading and simplified human body numerical models were validated using impulse, peak acceleration and the Head Injury Criterion from experimental blast test data. A study was then undertaken to evaluate head response at varying distances and orientations from the explosive. The accelerations and injury metrics for the head increased with decreasing distance to the explosive, as expected, but were also significant at intermediate distances from the explosive for larger charge sizes and intermediate heights of burst. Varying lateral position with constant standoff did not have a significant effect on the head kinematic response. The head injury criteria considered were exceeded in close proximity to the explosive (<35 charge radii) and depended on the height of burst for the range of charge sizes considered. The injury criteria were also exceeded at intermediate distances for larger charge sizes because of the influence of the mach stem. Although the injury criteria used in this study are typically applied to longer duration events, and may not be applicable for shorter duration blast loading, aggressive loading is predicted at small standoff distances and confirmed by the resulting head kinematics.

Numerical derivation of pressure–impulse diagrams for prediction of RC column damage to blast loads

Pressure–impulse ( P– I) diagrams are commonly used in the preliminary design or assessment of protective structures to establish safe response limits for given blast-loading scenarios. Current practice in generating the pressure–impulse diagram for structure components is primarily based on the simplified single degree of freedom (SDOF) model. The damage criterion is usually defined in terms of deformation or displacement response. Under blast loads, structures usually respond at their local modes, the equivalent SDOF system derived using the fundamental structure response mode might not be suitable. Moreover, structure is often damaged owing to brittle shear failure. In this case, the deformation-based damage criterion might not be able to give an accurate indication of local damage of a structural component. In this paper, a new damage criterion for RC column is defined based on the residual axial load-carrying capacity. A numerical method to generate pressure–impulse diagram for RC column is proposed. Parametric studies are carried out to investigate the effects of column dimension, concrete strength, longitudinal and transverse reinforcement ratio on the pressure–impulse diagram. Based on the numerical results, analytical formulae to predict the pressure–impulse diagram for RC column are derived. A case study shows that the proposed analytical formulae can be easily used to generate pressure–impulse diagram for RC columns accurately. The results are also compared with those obtained from the SDOF approach. It is shown that the proposed method gives better prediction of pressure–impulse diagram than the SDOF approach.

Pressure–impulse diagrams for elastic-plastic-hardening and softening single-degree-of-freedom models subjected to blast loading

Pressure–impulse (P–I) diagrams are commonly used in the preliminary design of protective structures to establish safe response limits for given blast-loading scenarios. In this paper, P–I diagrams of an elastic-plastic-hardening and an elastic-plastic-softening single-degree-of-freedom model are studied. The formal analytical procedure to establish P–I diagrams of such a system is explained. A dimensionless parameter has been used to categorize the response into elastic, elastic-plastic-hardening, elastic-plastic-softening, rigid-plastic-hardening and rigid-plastic-softening. Two different methods to derive and use P–I diagrams have been explained. The feasibility of representing the resistance function as bilinear has been studied with regard to resistance at yield and total area under the resistance curve as system characteristics and maximum displacement as response. An example is included to verify this simplification. Inverse ductility and hardening/softening indexes have been introduced as dimensionless parameters to generalize the solution to all elastic-plastic-hardening and softening systems. Parametric studies have been conducted on the influence of inverse ductility and hardening/softening index on P–I diagrams and it was observed that the blast energy per unit of maximum displacement increases as inverse ductility increases or as hardening index increases (softening index decreases). Small variations in P–I diagrams have been observed with respect to softening index which implies low sensitivity of P–I diagrams with respect to this parameter in the studied range.

Blast loading and building robustness

AbstractAn overview of methods of blast load quantification and aspects of building design intended to reduce the damaging effects of explosions by increasing robustness is presented. Possible blast loading scenarios range from simple free‐air bursts, loading essentially isolated buildings, to complex urban environments, with road junctions and side streets, etc., where buildings have varying amounts of frangible facade. The blast loads resulting in these scenarios are radically different, with different aspects of the pressure load dominating the type and extent of building damage. Means of calculating these time‐varying pressure loads are described.Achieving stand‐off between a vulnerable building and the source of an explosion is the single most important factor in reducing the blast load experienced by the building. Methods of achieving stand‐off in building design are discussed. The creation of adequate stand‐off may often not be possible, and the need for robust glazing systems is also essential if blast is to be keep out of buildings and contamination of the work‐place by broken glass is to be prevented. The use of laminated glass, anti‐shatter film and other measures is discussed.Existing buildings pose particular problems to engineers concerned with their protection. Several methods of strengthening or increasing the effective mass of existing buildings are described.