Browsing by Author "John W. Baugh, Committee Member"

Filter results by typing the first few letters
Now showing 1 - 2 of 2
  • No Thumbnail Available
    Micromechanics-based Multiscale Lattice Modeling of Fatigue Cracking in Hot Mixed Asphalt
    (2003-10-08) Feng, Zhen; John W. Baugh, Committee Member; Robert E. White, Committee Member; Murthy N. Guddati, Committee Co-Chair; Y. Richard Kim, Committee Chair
    This dissertation presents a novel micromechanics-based lattice procedure designed to characterize the cracking performance of hot mix asphalt (HMA) from its constituent material properties. The approach essentially consists of a series of direct-lattice models integrated with multiscale technique. A typical direct-lattice modeling starts with a preprocessor that discretizes the microstructure of a specimen, which is either physically or virtually fabricated, into a random truss lattice. The mixture performance can be predicted by analyzing such lattice network using a general-purpose finite element program FEP++. The cracking process in HMA is simulated by successive removal of failed links representing microcracks. In this study, a surface energy based failure criterion is developed to trigger the creation and subsequent extension of microcracks. Due to the disparate length scales associated with microcracking and specimen size, the direct-lattice modeling described above would demand unrealistic computational cost for modeling even a laboratory scale HMA specimens. In order to make the procedure more practical, the multiscale approach is implemented. Essentially, multi-scale model considers the effect of different-sized aggregates at different length scales. Such an approach reduces the computational cost significantly, while capturing the mechanical phenomenon at various length scales. Finally, the effectiveness of the proposed multiscale lattice procedure is illustrated by modeling an actual indirect tensile (IDT) test on a thin cylindrical HMA specimen and making quantitative comparisons with experimental measurements, including full-strain fields measured by the digital image correlations (DIC) technique.
  • No Thumbnail Available
    Optimizing Roof Maintenance and Replacement Decisions
    (2006-01-05) Al-ibrahim, Anwar Adel; Salah E. Elmaghraby, Committee Member; David W. Johnston, Committee Chair; John W. Baugh, Committee Member; Michael L. Leming, Committee Member
    The objective of this research is to develop a Decision Support System that helps allocation of available funds to optimize roof maintenance strategies. The Decision Support System analyzes different maintenance alternatives available for each roof element and chooses the alternative that maximizes the benefits due to savings resulting from postponing element replacement. The analysis uses the Life-Cycle Cost to calculate the Reduction in Uniform Annual Cost (RUAC) that is used as the economical decision criterion to select the most economical maintenance alternative for each roof element at different condition states. The analysis utilizes integer linear programming to optimize the selection of maintenance actions for the different elements by maximizing the RUAC under budgetary constraints. Excel and AMPL software are used to implement the analysis. This study uses the roofing systems of 28 buildings on the North Carolina State University campus as a model to develop the Decision Support System. Parameters necessary to develop the model are estimated. The analysis is tested on the available data base.