International Journal of Protective Structures

Gabion structures are widely used for force protection as they enable locally available material to be used, reducing logistical expense. The soil fill within these structures provides the blast and ballistic resistance; hence, any localised variation in the contained soil can potentially lead to reductions in protective capability. Specifically, built gabion structures were monitored in internal and external environments to assess the variation of soil moisture content and density over a full year and with changing weather conditions. The gabions were filled with fine sand according to manufacturer’s instructions. Internal and external moisture content readings were recorded at regular intervals, and a continuously monitoring weather station was installed to collect comparative data. LIDAR scanning was used to record the shape and volume of the gabions to estimate variations in the density of the soil fill. The data indicate that moisture content can vary by over 20% between the top and base of the gabion, and by over 5% from face to face and between readings depending on recent weather conditions, while the core of the gabions remains relatively unaffected. This leads to localised variations in density which can impact on both the ballistic performance and blast resistance of the structure.

A novel layered concrete structure with an air gap was proposed to resist explosion attacks from terrorist bombings or conventional weapons. The proposed layered structure potentially benefits mitigating the blast wave induced from detonation in the predamaged concrete shelter layer by projectile penetration, because the wave impedance between air and concrete material is far different. To quantitatively evaluate the blast mitigation effects and reveal the blast-resistant mechanism, a fine numerical model of the proposed layered structure was built in LS-DYNA, in which trinitrotoluene explosive was detonated in predamaged concrete shelter at different depths. The developed model was validated by field tests of concrete slab under contact explosion. Failure mode of concrete shelter and pressure time histories on the protective structure layer were captured and compared. The distinct blast mitigation effect of the proposed layered structure was demonstrated. A parametric study on the perforation limit, height, and residual depth of concrete shelter was also performed. The calculated results revealed that trinitrotoluene explosive detonated at the impact perforation limit of concrete shelter by projectile penetration is a dangerous critical condition that may cause negative effects on blast mitigation. The blast mitigation rates can always exceed 99%, as long as the concrete shelter is not blasted to perforation. A fitting formula to obtain a higher blast mitigation rate in guiding the design of a layered concrete structure with an air gap was put forward.

Subjected to normal and oblique impact by copper explosively formed projectile which is a kind of easy-deformable and soft projectile, ballistic performance of a 40-mm thickness steel target has distinct characteristics compared with the dynamic deformation of target penetrated by a rigid projectile. The failure modes of steel targets change from perforation to embedment or ricochet as the angle of obliquity increases. Correspondingly, microstructure evolution of the crater wall and morphology feature of fracture surfaces are analyzed to reveal different failure mechanisms of steel targets. The results show that the finite steel target experiences the failure mode of plug before the obliquity reaches 15° and thereafter the copper explosively formed projectile will be embedded into the crater bottom causing a big bulge on the rear surface of the steel target at low obliquities. At high angles of obliquity, the main body of copper explosively formed projectile will be ricocheted along the front surface of steel target and the critical angle of projectile ricochet is found to lie in 50° to 60° in our study. The penetration efficiency and capability of explosively formed projectile decreases as the obliquity angle increases. The results will not only help to reveal penetration mechanisms of explosively formed projectile against metallic target but also help to improve the ballistic resistance of armors.

Accidents involving collisions of heavy-duty trucks with highway bridge piers occurred occasionally, in which the bridge piers might be subjected to severe damage, and cause the collapse of the superstructure due to the loss of axial loading capacity. The existing researches are mostly concentrated on the light- or medium-duty trucks. This article mainly concerns about the collisions between the heavy-duty trucks (e.g. tractor-trailer) and bridge piers as well as the evaluation of the impact force. First, by modifying the finite element model of Ford F800 single-unit truck, which was developed by National Crash Analysis Center, the finite element model of a tractor-trailer is established. Then, the full-scale tractor-trailer crash test on concrete-filled steel pier jointly conducted by Texas Transportation Institute, Federal Highway Administration, and Texas Department of Transportation is numerically simulated. The impact process is well reproduced and the established model is validated by comparison of the impact force. It indicates that the tractor-trailer impact force time history consists of two or three peaks and the corresponding causes are revealed. Furthermore, the parametric influences on the impact force are discussed, including the diameter and cross section shape of the pier, cargo weight, impact velocity, relative impact position, and vehicle type. Finally, the finite element model of an actual reinforced concrete highway bridge pier is established, and the impact force and lateral displacement of the pier subjected to the impact of the tractor-trailer are numerically derived and discussed.

This work presents the first fully validated and predictive finite element modeling framework to generate the probabilistic penetration response of an aramid woven fabric subjected to ballistic impact. This response is defined by a V₀-V₁₀₀ curve that describes the probability of complete fabric penetration as a function of projectile impact velocity. The exemplar case considered in this article comprises a single-layer, fully clamped, plain-weave Kevlar fabric impacted at the center by a 0.22 cal spherical steel projectile. The fabric finite element model comprises individually modeled three-dimensional warp and fill yarns and is validated against the experimental material microstructure. Sources of statistical variability including yarn strength and modulus, inter-yarn friction, and precise projectile impact location are mapped into the finite element model. A series of impact simulations at varying projectile impact velocities is executed using LS-DYNA on the fabric models, each comprising unique mappings. The impact velocities and outcomes (penetration, non-penetration) are used to generate the numerical V₀-V₁₀₀ curve which is then validated against the experimental V₀-V₁₀₀ curve obtained from ballistic impact testing and shown to be in excellent agreement. The experimental data and its statistical analysis used for model input and validation, namely, the Kevlar yarn tensile strengths and moduli, inter-yarn friction, and fabric ballistic impact testing, are also reported.

An approximate approach is developed to estimate the residual carrying-capacities of fire and near-field blast-damaged reactive powder concrete-filled steel tube columns. The single-degree-of-freedom model is employed to calculate the initial deflections of fire-damaged reactive powder concrete-filled steel tube columns subjected to axial and blast-induced transverse loads, and then a modified formula including double coefficient is further proposed to predict the ultimate resistance. Then, a series of blast-resistance and load carrying-capacity tests on six large-scale reactive powder concrete-filled steel tube columns are conducted to validate the suitability of theoretical method presented in this article. Blast tests demonstrate that the blast-resistances of reactive powder concrete-filled steel tube columns are more sensitive to fire durations than to scale distances. In addition, it is indicated that ISO-834 standard fire exposures cause significant degradations of material properties and have remarkable effects on the residual carrying-capacities of reactive powder concrete-filled steel tube columns. No local bucking and burst could be observed in the residual carrying-capacity tests; also, there are no visible hinge-like deformations in the mid-span area, and the excellent fire-resistances and blast-resistances of reactive powder concrete-filled steel tube columns are experimentally verified. Analytical results show that the predicted axial load capacities of six reactive powder concrete-filled steel tube columns are in good agreement with experimental data. All damage indices of the test specimens are within 0.8, meaning only minor to severe damage is done to the reactive powder concrete-filled steel tube column during fire and blast attacks, which is consistent with the test results.