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.

Characterisation of buried blast loading.

While it is well known that detonation of shallow-buried high explosive charges generally results in above-surface loading which is greatly amplified compared with the same detonation in air, uncertainty persists as to the mechanisms leading to this effect. The work presented in this paper is a systematic investigation into the mechanisms of load transfer in buried blast events. This paper details the results from a parametric study into the mechanisms and magnitudes of load transfer following a shallow-buried explosion, where spatial and temporal load distributions are directly measured on a rigid surface using an array of Hopkinson pressure bars. In particular, the investigation has looked at the influence of both geometrical confinement and geotechnical conditions on the loading. The parametric study was separated into four main threads: the influence of physical confinement; gravimetric moisture content; stand-off distance and depth of burial; and soil material/particle size distribution. This study allows a direct observation of the contributions of each of these distinct parameters, and in particular the ability to discern how each parameter influences the temporal form and spatial distribution of the loading.

Theoretically optimal forms for very long-span bridges under gravity loading.

Long-span bridges have traditionally employed suspension or cable-stayed forms, comprising vertical pylons and networks of cables supporting a bridge deck. However, the optimality of such forms over very long spans appears never to have been rigorously assessed, and the theoretically optimal form for a given span carrying gravity loading has remained unknown. To address this we here describe a new numerical layout optimization procedure capable of intrinsically modelling the self-weight of the constituent structural elements, and use this to identify the form requiring the minimum volume of material for a given span. The bridge forms identified are complex and differ markedly to traditional suspension and cable-stayed bridge forms. Simplified variants incorporating split pylons are also presented. Although these would still be challenging to construct in practice, a benefit is that they are capable of spanning much greater distances for a given volume of material than traditional suspension and cable-stayed forms employing vertical pylons, particularly when very long spans (e.g. over 2 km) are involved.