Air-blast effects on civil structures
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The effects of detonations of high explosives are the focus of this dissertation. Analyses are performed using computational fluid dynamics (CFD) and finite element codes, theoretical formulations and empirical data. The effects of detonations of high explosives at (TNT) radial expansions of less than 7 (or Z ≤ 0.37 m/kg 1/3 ) are characterized in terms of incident and reflected overpressures and impulses. Calculations are performed to verify a CFD code; estimate blast effects using 1D models; predict incident overpressures and impulses; provide guidance on the use of reflecting and transmitting boundaries in 2D and 3D models, and provide recommendations on cell size for CFD analysis. The complex wave field in the Mach stem region is studied. Air-blast parameters, including incident and reflected overpressures and impulses, are typically estimated for protective design using charts developed by Kingery and Bulmash. The charts underpredict incident and normally reflected overpressures and incident impulse near the face of the charge. Numerical analyses of detonations of spherical charges of TNT in free air are performed to understand the shortcomings of current approaches and to provide data for the development of new equations and design charts for incident and normally reflected overpressures and impulses and for shock-front arrival time. Reflection coefficients are often used to transform incident overpressures to reflected overpressures; these coefficients vary as a function of the angle of incidence. Values for the reflection coefficient are available in textbooks and technical manuals but these values vary by document, especially in the region of Mach reflection. Numerical studies are presented to resolve differences between the documents. Recommendations for design practice are provided. Material erosion is often used for simulations of extreme damage to structural components, and elements are eroded from a finite element mesh based on user-specified criteria. Single element simulations of concrete are performed to establish reliable values of concrete erosion strain as a function of strain rate, compressive strength, element size and loading condition. Numerical simulations of a sample reinforced concrete column subjected to blast loadings are undertaken to demonstrate the utility of the proposed erosion criteria and to characterize, for a single case, the importance of concrete compressive strength, transverse reinforcement, and axial load on estimations of damage.