Denis D. Rickman

Development of an Improved Methodology for Predicting Airblast Pressure Relief on a Directly Loaded Wall

The interaction of an airblast wave with a structure, and the blast wave propagation around and over the structure is of significant importance. In order to protect a structure from the airblast produced by such explosive threats as terrorist bombs, a facility designer must possess an adequate knowledge of the expected blast wave loading. Of greatest importance are pressures and impulses on the directly loaded face of the structure, since it is typically subjected to the highest (reflected) pressures. It has long been recognized that reflected pressure time histories can be strongly influenced by pressure relief from the free edges of the loaded wall. The relief wave can significantly reduce the magnitude of the late-time portion of the positive reflected pressure phase, resulting in a substantial decrease in the peak impulse load. Most current predictive methodologies attempt to account for the relief wave and its effect on impulse. Unfortunately, these methods tend to be rather inaccurate because the exact manner in which the relief wave is manifested is not accurately defined. The US Army Engineer Research and Development Center has developed an improved methodology to predict the effect of pressure relief. This paper presents the basis for the methodology and its practical application.

The Influence of Soil Parameters on the Impulse and Airblast Overpressure Loading above Surface-Laid and Shallow-Buried Explosives

The dynamic airblast, fragmentation, and soil ejecta loading environments produced by the detonation of surface-laid and shallow-buried mines are major threats to lightweight military vehicles. During the past several years, the US Army has focused considerable attention on developing improved methods for predicting the below-vehicle environment from these threats for use by vehicle/armor analysts; thereby, improving the survivability of these platforms. The US Army Engineer Research and Development Center recently completed the first year of a three-year effort to experimentally and numerically quantify the blast and fragment loading environments on vehicles due to surface and subsurface mine and IED detonations. As part of this research effort, a series of experiments was conducted to quantify the effects of soil parameters on the aboveground blast environments produced by the detonation of aboveground bottom-surface-tangent, buried top-surface-tangent, and shallow-buried 2.3-kg (5-lb) Composition C4 charges. The experiments were conducted using three different well characterized soils; 10.8% air-filled-voids (AFV) silty sand, 5.4% AFV clay, and 29.8% AFV poorly graded sand. The combined aboveground loads due to airblast and soil debris were measured by an impulse measurement device. The near-surface airblast overpressure was quantified by a series of side-on measurements above the charges at one elevation and three radial distances. This paper summarizes and compares the results of the experimental program with emphasis on defining the effect of soil parameters on the aboveground blast environment.

Numerical Simulations of Explosive Wall Breaching

Explosive wall breaching will be a key war fighter capability in future military operations by dismounted soldiers in urban terrain environments where the close proximity of urban structures, possibly occupied by noncombatants, significantly restricts the use of large demolition charges or large caliber direct-fire weapons. The US Army Engineering Research and Development Center (ERDC) is currently investigating new explosive wall breaching systems and numerical techniques to model the breaching system interaction with the wall targets. The experimental and numerical programs will conduct comprehensive demolition breaching research on a full range of construction and material types and will fully validate new multi-functional breaching procedures across the spectrum of desired missions. As a first step in this process, the ERDC conducted a baseline study of C-4 breaching effectiveness against steel-reinforced concrete walls in FY04. The goal of this effort was to develop improved methods for breaching these walls with simple arrangements of C-4. The experimental breaching scenarios addressed: (1) a baseline study of C-4 breaching, (2) optimal use of C-4 for concrete removal, and (3) optimal use of C-4 for concrete and reinforcing steel removal. Numerical simulations of two selected experiments were conducted using the coupled Eulerian and Lagrangian code Zapotec. In these simulations, the concrete and reinforcing steel were modeled as Lagrangian materials, and the C-4 and air were modeled as Eulerian materials. Two different concrete constitutive models were used in the simulations: the Karagozian and Case concrete model, which is included with Zapotec, and the Microplane model, which was implemented in Zapotec by ERDC personnel. Comparisons between the experimental results and the numerical simulations will be described.

Numerical Simulations of Explosive Blast Pressures During Wall Breaching

During the past several years, the US Army has focused considerable attention toward developing improved methods for breaching walls and determining weapon-target interaction effects from direct- and indirect-fire weapons in the urban combat environment. A major thrust area is centered on developing methods for predicting the blast and fragmentation environment behind a breached wall. This information is important to the warfighter in terms of recognizing the expected impact on both enemy combatants, and non-combatants or friendly forces. One impediment to this effort is that little data exist to document the behind-wall blast environment produced by the detonation of explosives against or within walls. As part of the Armys effort, the US Army Engineer Research and Development Center (ERDC) is conducting experimental and numerical investigations to improve wall breaching methods. In the experimental and numerical programs, the ERDC conducts comprehensive research on a full range of urban construction materials. As a first step in this process, the ERDC conducted a baseline study of C-4 breaching effectiveness against steel-reinforced-concrete (RC) walls. A goal of this effort was to better define the behind wall blast environment produced by various C-4 charges placed in contact with RC walls. Numerical simulations of selected experiments were conducted using the coupled Eulerian-Lagrangian code Zapotec. In these simulations, the concrete and reinforcing steel were modeled as Lagrangian materials, and the C-4 and air were modeled as Eulerian materials

Breaching of Triple-Brick Walls: Numerical Simulations

Explosive wall breaching will be a key war-fighter capability in future military operations by dismounted soldiers in urban terrain environments where the close proximity of urban structures, possibly occupied by noncombatants, significantly restricts the use of large demolition charges or large caliber direct-fire weapons. Because of this requirement, the US Army has focused considerable attention and resources to optimize breaching activities in urban terrain. As part of the Armys effort, the US Army engineer research and development center (ERDC) is conducting experimental and numerical investigations to improve wall breaching methods. The ongoing experimental and numerical programs will conduct comprehensive breaching research on a full range of urban construction materials. As a first step in this process, the ERDC conducted a successful baseline study of Composition C4 (C-4) breaching effectiveness against steel-reinforced-concrete walls. Recently, the research effort was extended to triple-brick walls. Numerical simulations of two selected experiments were conducted using the coupled Eulerian- Lagrangian code Zapotec. In these simulations, the brick and mortar were modeled as Lagrangian materials, and the C-4 was modeled as an Eulerian material.

Uncertainties in Blast Loads on Structures

The first step in protecting the occupants of a building from the effects of the detonation of an explosive device by a terrorist is to determine the maximum charge weight that the terrorist could reasonably be expected to use. The next step is to determine a set of possible detonation locations that could cause critical design loads on the structure. For each charge weight and location selected, the design engineer typically uses design-manual-, engineering-code- or hydrocode-calculations to predict a deterministic set of pressure-time histories at various locations on the building. The load prediction method used depends primarily on the complexity of the explosive structure geometry. For simple geometries (an explosive charge placed on the ground at a reasonable standoff distance in front of a flat-faced building), the design manual or engineering code approaches are appropriate. For more complicated structures, or for structures very close to other structures, hydrocode calculations may be needed to accurately predict the loads because of shock wave reflection of other structures. Once the loads are predicted, a deterministic dynamic analysis is then performed to predict the response of the building.

Improved Predictive Methods for Airblast Shielding by Barrier Walls

Urban planners often consider the use of barrier walls as a means of protecting structures and other assets from terrorist vehicle bombs. Barrier walls offer a means of halting the approach of vehicle bombs, thereby limiting the proximity of the bomb to the at-risk asset. Depending upon their height and structural integrity, barrier walls may also provide significant shielding from the airblast produced by the bomb. Several methods exist for the prediction of this shielding effect. Unfortunately, these methods tend to be rather inaccurate, due primarily to the complexity of the airblast/barrier wall interaction, and to the lack of a comprehensive database upon which to form a predictive methodology. During the past four years, the US Army Engineer Research and Development Center has conducted an extensive series of small-scale experiments and hydrocode calculations to examine barrier wall shielding of structures. This database is now being used to develop an improved methodology to predict peak reflected pressure and impulse behind barrier walls of various heights for a wide range of explosive-to-wall and wall-to-structure distances. A wide range of target heights on the shielded structure are also addressed. This paper provides an overview of the experimental and computational database, and the new predictive methodology now under development.

Explosive Removal of Concrete From Reinforced Walls

During the past several years, the US Army has focused considerable attention toward developing improved methods for breaching walls in the urban combat environment. A major thrust area is centered on finding improved methods to breach the toughest wall type that Army units are likely to face: a double (steel) reinforced concrete (RC) wall. One impediment to this effort is that the relationship between the contact explosive charge configuration and the quantity of concrete removed has not been thoroughly understood. The U.S. Army Engineer Research and Development Center has conducted a research effort to better define the effectiveness of various explosive charge configurations in breaching RC walls. This paper presents a discussion of results from this research.© 2007 ASME

Development of an Improved Methodology for Predicting Airblast Pressure Relief on a Directly-Loaded Wall

The interaction of an airblast wave with a structure, and the blast wave propagation around and over the structure is of significant importance. In order to protect a structure from the airblast produced by such explosive threats as terrorist bombs, a facility designer must possess an adequate knowledge of the expected blast wave loading. Of greatest importance are pressures and impulses on the directly-loaded face of the structure, since it is typically subjected to the highest (reflected) pressures. It has long been recognized that reflected pressure time-histories can be strongly influenced by pressure relief from the free edges of the loaded wall. The relief wave can significantly reduce the magnitude of the late-time portion of the positive reflected pressure phase, resulting in a substantial decrease in the peak impulse load. Most current predictive methodologies attempt to account for the relief wave and its effect on impulse. Unfortunately, these methods tend to be rather inaccurate because the exact manner in which the relief wave is manifested is not accurately defined. The US Army Engineer Research and Development Center has developed an improved methodology to predict the effect of pressure relief. This paper presents the basis for the methodology, and its practical application.Copyright

Investigation of relationships between soil type and condition and crater size for shallow-buried explosive charges

The detonation of near-surface and shallow-buried explosives results in a ground crater that has a size and shape that is directly related to the charge size, charge position, and soil conditions. Several methods are currently available that attempt to predict crater size, that is, apparent depth and diameter of a ground crater, based on direct inputs of key factors such as the soil type, soil conditions, explosive type and mass, and depth of burial of the explosive. Current prediction methodologies are limited, primarily due to the lack of key cratering data in well-controlled and characterized soil backfills consisting of a full range of soil types, water contents, and density conditions. A new cratering database is currently being developed based on craters produced in well-characterized materials representing a significant number of soil types defined by the Unified Soil Classification System. This database is capturing key cratering measurements for charge depth of burials ranging from tangent below the ground surface to a scaled depth of approximately 1.0 ft/lb1/3. Data collected include water content and density measurements in the as-constructed backfills and measurements of the crater cross-sectional profiles, including the apparent depth and diameter, lip-to-lip diameter, and lip-to-bottom depth. Analyses were conducted on the test data to define key parameters affecting crater size. Based on the results of these analyses, the critical soil parameters affecting crater size were identified.