Ethan Steward, a doctoral candidate in explosives engineering, will defend their dissertation titled “Mid-Field Shock and Impulse Estimation Methods for Blast Loading on Tall Targets.” Their advisor, Dr. Kyle Perry, is an associate professor in the mining and explosives engineering department. The dissertation abstract is provided below.

Blast resistant structural design continues to be a major research area for governments around the world due to explosive threats from both state and non-state actors. Many of the typical targets of explosive attacks, such as government buildings, commercial high rise office buildings, and apartment complexes are mid to high-occupancy buildings that present a tall profile relative to the charge size and are often clad in curtain walls. Glass and aluminum curtain wall systems are commonly used to clad the exterior of government and commercial structures, allowing light into the building, regulating the interior environment, and providing an aesthetically pleasing exterior. These systems are likely to fail when exposed to sudden, high-pressure events such as the purposeful or accidental detonation of explosives. Engineers have designed blast resistant curtain walls and structural elements to reduce the likelihood and severity of failure, but the design tools and testing mechanisms commonly used in the process may not accurately model or simulate actual blast conditions at all ranges.

In blast resistant structural design, the origin of a shock wave is typically assumed to be in the far-field, creating a wave that is nearly planar and parallel to at least one face of the target. Shock is applied evenly and immediately across the entire impacted surface. However, the source of real-life blasts is often very close to the target structure and the assumption of far-field planar shock does not always apply. Empirical data from historical tests forms the basis for analysis, but that data was gathered from large multi-ton tests and may not accurately predict blast parameters from scaled tests. This research examines scaled “mid-field” blasts which exhibit characteristics different from those assumed about far-field shocks from large scale detonations, specifically a hemispherical shock that produces different peak pressures, impulse curves, oblique reflections, and Mach stems across a target. Additionally, because the shock from a mid-field surface burst will first impact the bottom of a tall structure, vibrations will propagate through the curtain walls and structural elements far faster than the shock will arrive because the speed of sound in solids is much greater than the speed of air shocks. Shock induced vibration may have adverse effects on the blast resistance of the structure.

This research examines mid-field blast parameters from small-scale and full-scale blasts by measuring reflected and incident pressure and impulse. Results will be compared to theoretical blast parameter equations and empirical data used by the industry. Further refinements to blast parameter estimation will be suggested.