Multi-scale & multi-resolution experimental and analytical methods for mitigating blast risk with barrier walls
Date
2024
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Abstract
Over the last decade, interest in blast resistance and protection has increased as a result of the perpetual threat of terrorist groups around the world. In evaluating the Department of State (DOS) reports on terrorism since 2007, an estimated 330,000 fatalities and 430,000 injuries have been caused by terrorist attacks worldwide (2022). In the United States, various large scale explosive attacks have occurred over the years including the World Trade Center bombings in 1993, the Alfred Murrah Federal Building bombing in 1995, and the coordinated September 11th attacks in 2001. More recently, there has been a shift in the tactics of terrorist groups to use improvised explosive devices (IEDs) to target civilians due to regulations put in place after the September 11th, 2001, attacks that made it difficult for them to obtain a large amount of explosive material among other factors contributing the rise of terrorist activity. Attacks such as the Boston Marathon bombing in 2013 and the Madrid train bombing in 2004 demonstrate this shift in tactics. The upward trend of the use of IEDs around the globe since the September 11th, 2001, attacks presents a catalyst for a shift in research methods for blast mitigation techniques to provide protection to people rather than just structures. Therefore, developing methods to provide protection for people from blast effects is necessary to minimize the impact these terrorist groups have on our communities. Of the existing blast mitigation strategies, perimeter walls or barriers are specifically advantageous in that they increase standoff distances and provide an obstacle to the propagation path of the blast wave as well as primary fragmentation. The use of perimeter walls or barriers to protect structures has been well established in literature, however the use of barriers to protect people has not. The ability to predict airblast effects accurately and efficiently over a large variation in scaled ranges, within a complex environment, is important to characterize the potential severity of damage to structures and casualties among personnel in both military and civilian settings. Many different techniques have been used over the years to perform blast prediction of various airblast parameters such as pressure and impulse and blast resistant design research. While experimentation remains a valuable and powerful tool, in recent years, computational and numerical models have grown in popularity for their accurate evaluation capabilities. Advanced numerical software such as hydrocodes and computational fluid dynamic programs are often used to model airblast propagation and its impact on structures. However, in more complex environments, where blast loading in large areas of interest may occur, using high-fidelity computational modeling software could be inefficient due to the computing power required. The goal of this dissertation was to develop a performance-based design framework for predicting the probability of survivability of a double-barrier system under blast loading, and the probability of different bodily injuries for personnel from the blast wave itself. In this dissertation, the gaps in research for protecting civilians from IED attacks in large open areas, understanding the impact of multiple barriers on the blast shockwave and pressures around the barriers, and investigating an absorption focused barrier were addressed. A combination of analytical, numerical, and experimental methods at multiple scales was used to develop and validate the various elements needed to conduct the performance-based design. This dissertation developed rapid computational models to predict the pressure field around a double-barrier system, analyzed a new barrier design that focuses on reducing the energy of the shockwave in order to protect people, and accounted for the uncertainty and variability in multiple parameters to establish potential risk for various scenarios for both the barrier and for people. The analyses combined numerical, analytical, and experimental methods at multiple scales, to create models to predict and assess the pressures associated with person-borne-improvised-explosive-devices (PBIEDS). The developed models used to predict and quantify the pressures around a rigid double-barrier system and the response of the wood barrier to blast loading were coupled with small- and full-scale experimental testing to validate and assess the accuracy and efficiency of the models. From the results of dissertation, it can be observed how the implementation of a double-barrier system can significantly reduce the pressures experienced around the barriers, which can lead to less potential for serious injury or damage from blast events. Additionally, it showed that the distance between the barriers plays a critical role in the pressures and therefore the potential for injury between the barriers. In addition, adopting an innovative approach to blast barrier design to consider the use of more lightweight, commonly available, non-rigid materials to increase the energy absorption to attenuate the blast shockwave rather than just reflect was proven to be beneficial.
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Subject
experimentation
performance based design
structural analysis
finite element analysis
blast
pressure prediction