<p>Aravind Srinivasan. Scheduling and Routing for Demand Responsive Transit Operations. (Under the direction of Dr. John W. Baugh and Dr. John R. Stone.)The multi-vehicle dial-a-ride problem has been proven to be intractable and NP-hard. Researchers have proposed numerous techniques for furnishing approximate solutions, but most ofthese aim at conquering a single objective, such as minimization of eet size. The chosen technique must handle multiple (different or competing) objectives that characterize the problem, so that it may lend itself as a tool in transit research. This thesis explores a new technique based on the cluster-first, route-second strategy, where the multiple competing objectives of the dial-a-ride problem are successfully addressed. The key highlights in this technique are the development of different routers for different stages of the optimization, and organism filters to guide the population of prospective solutions in the clustering phase of the optimization. Application and comparison to case study data indicate that the techniques developed outperform a commercial scheduling package in generating optimal schedules, and lend themselves to configuration and customization in order tosimulate different scenarios, which help in selecting demand-responsive transit policies.<P>

<p>This dissertation presents the viscoelastic characterization of asphalt concrete in indirect tensile testing and the development of a simple performance test for fatigue cracking. The analytical solutions to calculate creep compliance and center strain from displacements measured on the specimen surface were developed based upon the theory of viscoelasticity. These developments were verified by 3-D finite element viscoelastic analysis and tests. A simple performance test was developed based on these solutions and work potential theory. To evaluate its validity, the indirect tensile tests were performed on WesTrack asphalt mixtures varying aggregate gradations, asphalt contents, and air void contents. Fracture energy obtained from indirect tensile strength testing and creep testing was highly correlated with field performance of these mixtures at WesTrack. A combination of indirect tensile creep and strength testing was proposed as a simple performance test for fatigue cracking. Recommendations for expanding the applicability of the simple performance test developed are provided.<P>

<p>BAMMI, SACHIN. Quantitative Analysis of Variability and Uncertainty in On-Road and Non-Road Mobile Source Emission Factors. (Under the direction of Dr. H Christopher Frey.) The goal of this research is to demonstrate a methodology for quantifying variability and uncertainty in mobile source emissions. Emission factors and emission estimates are subject to both variability and uncertainty. Variability in emissions deals with real differences in emissions among multiple emission sources at any given time or over time for any individual emission source. Variability is the heterogeneity of values of a quantity with respect time space or across a population. Uncertainty in emissions on the other hand implies the lack of knowledge regarding the true value of emissions. In this research variability and uncertainty are treated separately since their sources are different and as such they affect the decision making process in a different way. For example, sources of variability in mobile source emissions include: vehicle make; ambient temperature; vehicle model; fuel used; vehicle age; and/or driving behavior. Sources of uncertainty may include: small sample sizes; lack of precision and/or accuracy in measurements; non-representativeness; or lack of data. In this work a methodology for simultaneous characterization of variability and uncertainty in mobile source emission factors is described. Variability is characterized by fitting probability distributions to the data sets. Uncertainty due to random sampling error is characterized by using the parametric Bootstrap technique.This methodology is demonstrated for emission factors for three categories: (1) Onroad mobile source exhaust air toxic emissions (2) nonroad lawn and garden equipment emissions and (3) nonroad construction farm and industrial equipment emissions. For the first category a database of vehicular exhaust emissions developed by the California Air Resources Board (CARB) was used. For the second and third categories emission factor databases were developed by reviewing reports and/or technical papers from U.S. Environmental Protection Agency (EPA), Southwest Research Institute (SwRI), CARB and Society of Automotive Engineers (SAE).The main results regarding the demonstrated methodology and related statistical analysis in this research include: (1) emission factor groupings were determined statistically (e.g. by engine size for lawn and garden engines); (2) substantial inter-engine variability in emissions was discovered; and (3) large ranges of uncertainty in mean emissions were found in many cases. In particular, uncertainty ranges for the mean emission factors were in excess of ±20 percent in most cases and as high as minus 49 percent to plus 89 percent.<P>

<p>TAN, YING. Experimental and Nonlinear FEA Investigation of Elbows Leading to a New Definition of The B2 Stress Index (Under the supervision of Dr. Vernon C. Matzen).This study suggests a new margin-consistent procedure for the calculation of the B2 stress index for any piping component, which is the ratio of the collapse moment of a corresponding straight pipe to the collapse moment of the piping component. It gives a B2 value of 1.00 when applied to a straight pipe and a safety margin for the component that is always the same as for the straight pipe. An example of using this definition to calculate the value of B2 is provided. To obtain the collapse moments of piping components, either finite element analysis (FEA) or experiments can be used. This work gives a brief review of nonlinear FEA modeling procedures. Then nonlinear FEA using ANSYS shell models and ABAQUS elbow models are used to simulate two tests on straight pipes and eight tests on elbows under in-plane closing, in-plane opening and out-of-plane bending. Constitutive models and welding effects are discussed. All correlations between FEA and measured experimental results for the load-displacement curves are excellent. It is concluded that nonlinear FEA using ANSYS SHELL181 and ABAQUS ELBOW31 can give quite accurate predictions of the global behavior of elbows and straight pipes under monotonic loading. A very preliminary study for B2' stress index for cyclic loading is also performed, in which two elbow tests subjected to quasi static in-plane cyclic loading were simulated. <P>

<p> Since the advent of diesel fuel use, insufficient storage and inadequate transport and disposal practices have resulted in widespread contamination of the subsurface environment. Beginning in the 1970?s, the United States EPA has established a number of regulations controlling current and future storage, transport, and disposal efforts and address the need to remediate existing contaminated sites. However, regulations provide only the desired goal, not a roadmap of how to accomplish remediation. It falls then, to individuals in research and industry, to devise techniques effective in reducing / eliminating contamination levels at sites of concern. Existing remediation techniques of pump and treat and air sparing / soil vapor extraction are effective, but often take many years to accomplish remediation to regulatory levels. Thermal treatments such as steam stripping and electrical heating of soils, are much less time consuming, but much more costly endeavors. Low temperature thermal desorption (at temperatures less than 80 degrees C) holds promise by incorporating the benefits of higher temperatures, such as the increase in vapor pressure and the decrease in viscosity, without the extreme cost usually associated with thermal treatments. In order to test this hypothesis, a research testing program focused on batch testing in the laboratory setting was developed to assess the viability of increased temperatures on the desorption efficiency of benzene on various soils. Testing consisted of three soils, a poorly graded Ottowa sand, kaolinite, and a natural silty sand soil from the Lockbourne Air Force Base experimental testing site. The contaminant of concern is benzene, a carcinogenic and mutagenic compound that is one of the four major components of BTEX, a constituent of most diesel fuels. Benzene was chosen because of its presence at the LAFB testing site at contamination levels 164 times groundwater regulation limit of 5 ppb. Laboratory testing was conducted at initial benzene solution concentrations of 10, 100 and 1000 mg/L. Four temperatures; 20, 40, 60, and 80 degrees C, were used in the batch testing program. Results from testing support the theory that increased temperatures result in higher desorption efficiency. For lower concentrations of 10 and 100 ppm, temperatures as low as 40 degrees C correlated to increases in desorption levels from 40 percent (at 20 degrees C) to over 80 percent for the kaolinite and natural soil. Sand also experienced a doubling in desorption efficiency (from roughly 30 percent to roughly 70 percent) at the 60 degrees C temperature and 10 and 100 ppm concentrations. The 1000 ppm testing concentration resulted in more modest, but still increasing removal efficiencies at increased temperatures. Remediation at moderately increased temperatures appears to be a promising technique, but further research needs to be performed on soils that have experienced long term exposure to contamination to assess whether or not increased desorption efficiency trends are maintained. <P>

<p>PARK, HEE MUN. Use of Falling Weight Deflectometer Multi-Load Level Data for Pavement Strength Estimation. (Under the direction of Y. Richard, Kim).The objective of this study is to describe a mechanistic-empirical approach to developing an analysis method for assessing pavement layer conditions and estimating the remaining life of flexible pavements using multi-load level Falling Weight Deflectometer (FWD) deflections. A dynamic finite element program, incorporating a stress-dependent soil model, was developed to generate the synthetic deflection database. Based on this synthetic database, the relationships between surface deflections and critical pavement responses, such as stresses and strains in each individual layer, have been established.A condition assessment procedure for pavement layers using multi-load level FWD deflections is presented in this study. The results indicate that the proposed procedure can estimate the base and subgrade layer conditions. However, large variations were observed in the relationships between the DBCI and desg values and the subgrade CBR values for aggregate base pavements. A FWD test with a load of 53 kN or less does not result in any apparent nonlinear behavior of the subgrade in aggregate base pavements. With regard to the condition assessment of the asphalt concrete (AC) layer, the AC layer modulus and the tensile strain at the bottom of the AC layer are found to be better indicators than the deflection basin parameter.The procedures for performance prediction of fatigue cracking and rutting are developed for flexible pavements. The drastically increasing trend in fatigue cracking with time may not be predicted accurately using the proposed procedure. Such trends may be due to the environmental effects and the inconsistent distress measurements. Predicted rut depths using both single and multi-load level deflections show good agreement with measured rut depths over a wide range of rutting potential. However, the procedure using single load level deflections consistently underpredicts the rut depths. This observation demonstrates that the rutting prediction procedure using multi-load level deflections can estimate an excessive level of rutting quite well and, thus, improve the quality of prediction for rutting potential in flexible pavements. <P>

<p>Among the many models and tools available for solid waste management (SWM), the integrated SWM decision support tool (ISWM DST) developed at North Carolina State University provides a comprehensive and integrated approach that considers cost and environmental factors associated with a large set of waste processing options. ISWM DST is designed to generate alternative SWM strategies that meet user-defined cost and environmental objectives. In addition to an array of site-specific inputs, this tool includes a large number of model parameters, which are currently treated deterministically with point estimates for inputs. A high degree of variability and uncertainty is known to exist in these input parameters, affecting the uncertainty in the model outputs. The absence of a systematic procedure to consider uncertainty in ISWM DST is a major drawback. The goal of this study is to develop and incorporate an uncertainty analysis component into ISWM DST. A Latin Hypercube Sampling (LHS) procedure is coupled with a simulation approach to enable uncertainty propagation. The capabilities of this new component are demonstrated using a realistic case study in which a series of scenarios are examined assuming uncertainty in a subset of the input parameters. For each scenario, the alternative strategy development capabilities of ISWM DST is first applied, the then each SWM strategy is evaluated under conditions of uncertainty. Performance of alternative strategies is compared, and more reliable or robust strategies are identified. New and useful insights that were not apparent under deterministic conditions were gained, contributing more information to assist in SWM decision making. Further, correlation analysis was conducted to identify the uncertain input parameters that contribute mostly to the output uncertainty. This information is also expected to be valuable in making more informed decisions. In summary, this research contributes by significantly enhancing via the uncertainty analysis component the broad array of powerful capabilities of ISWM DST, making this tool more applicable in SWM planning and design practice. <P>

<p>A small scale test apparatus to measure the total lateral pressure and pore pressureof fresh mortar under an applied pressure over time was developed at the North CarolinaState University Constructed Facilities Laboratory. The effects of selected materialcharacteristics and construction factors on the lateral pressure were examined. Theresults were compared to numerical models developed by others to predict the maximumlateral pressure exerted by concrete to be used for the design of concrete formwork. Inaddition, principals and concepts from concrete chemistry and soil mechanics wereexamined to attempt to understand the mechanics of the lateral pressure of fresh concrete.The research is conducted with the objective of developing a small scale test which willallow factors affecting lateral pressure from fresh concrete on formwork to be exploredprior to conducting full scale tests.<P>

<p>Research work is conducted to investigate the possibility of using laboratory model tests to simulate lateral response of drilled shafts embedded in soft weathered rock and discern their P-y curve function. Eight lateral load tests on instrumented model piles embedded in an Aggregate Base Course (ABC) medium are performed to evaluate the P-y curves. The ABC material is selected to simulate the response of soft weathered rock encountered in the field. The laboratory-evaluated P-y curves are compared to data from full-scale field tests performed in weathered rock. The two key parameters evaluated are the modulus of subgrade reaction (kho) and the ultimate lateral resistance (Pult). Using the laboratory-measured data, in comparison to measured field behavior, correlations for the subgrade modulus as a function of depth, as well as simplified approximations of Pult are developed for weathered rock materials. Results indicated that a hyperpolic P-y function seems to best represent the measured laboratory P-y curves. A comparison between laboratory and field data indicated that the ABC testing medium appears to yield kho and Pult that behave in a fashion similar to weathered rock material. Accordingly, it seems that, when appropriately mixed, that ABC can be used to model SWR encountered in the field. A distribution of kho with applied confining stress is evaluated and compared to results from procedures proposed by Reese (1997) for weathered rock and Terzaghi (1955) for stiff clay. A relationship developed for the distribution of subgrade modulus as a function of depth compared well with field data. The relationship of Pult with depth as a function of Geological Strength Index (GSI) and friction angle is also presented. All results are viewed in the context of the field measured response. <P>

<p>Identification and qualitative comparison of sensitivity analysis methods that have been used across various disciplines, and that merit consideration for application to food safety risk assessment models are presented in this paper. Sensitivity analysis can help in identifying critical control points, prioritizing additional data collection or research, and verifying and validating a model. Ten sensitivity analysis methods, including four mathematical methods, five statistical methods and one graphical method, are identified. Application of these methods was also illustrated with the examples from various fields. These methods were compared on the basis of their applicability to different types of models, computational issues such as initial data requirement, time requirement, and complexity of their application, representation of the sensitivity, and the specific uses of these methods. No one method is clearly best for food safety risk models. In general, the use of two or more methods may be needed to increase confidence on the rank ordering of key inputs.To identify specific issues with respect to the application to a typical food safety risk model, the sensitivity analysis methods were applied to the risk assessment model of the public health impact of vibrio Parahaemolyticus (the Vp model). The Vp model was modified so that proper sensitivity analysis can be done on independent inputs. The results of the sensitivity analyses were interpreted and discussed in detail. The rank ordering of key inputs was reasonably similar for most of the methods. For example, five of the seven methods ranked water temperature, the number of oysters per meal, and a new input IUR in the top three. Time on water and an input IG were identified as the least important inputs by six methods.<P>