Civil & Environmental Engineering

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Research from the Department of Civil & Environmental Engineering. The department website may be found at https://www.ndsu.edu/ce/

The Civilian is the newsletter for the Department of Civil Engineering and can be found at https://hdl.handle.net/10365/28260

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Now showing 1 - 20 of 103

Analysis and Evaluation of the Pedestrian Hybrid Beacon in School Zones
(North Dakota State University, 2010) Bittner, Michael Howard
Meeting dual objectives of pedestrian safety and motorist convenience at pedestrian crossings in school zones is an important and continuing challenge for all local communities. Pedestrian safety is influenced by pedestrian delays as well as motorist compliance of controls. Motorist convenience is influenced by the delay experienced by drivers. Conventional crosswalk control devices such as marked crosswalks and pedestrian signals are not always adequate or efficient in balancing these two crucial but conflicting objectives. The 2009 edition of the Manual on Uniform Traffic Control Devices (MUTCD) has paved the way for the use of a brand new crosswalk control device known as the pedestrian hybrid beacon (PHB). Previous research has provided evidence of this device's effectiveness in the area of motorist compliance and reduced motorist delay compared to traditional pedestrian signals. No prior research has been conducted on the PHB in the school zone context or on children pedestrians in general. This research has two objectives. The first objective was to analyze MUTCD Warrant 5 standards, which are designed for pedestrian signals in school zones, and the new PHB standards. This analysis will use pedestrian volume, vehicle volume, and gap availability on different test locations to conduct a comparative analysis of the two sets of standards. The purpose of this objective is to determine the transferability of the new MUTCD PHB standards in the school zone context. The second objective of this research was to evaluate three crosswalk control devices; marked crosswalks, pedestrian signals, and PHBs, for their ability to effectively address pedestrian safety and motorist convenience at school crossings. It was found that the PHB performed significantly better than traditional marked crosswalks but not markedly different than conventional pedestrian signals in the ability to balance the objectives of pedestrian safety and motorist convenience. The absence of improvements in performance of the PHB when compared to the pedestrian signal can be attributed to the fact that only 8.8% of motorists correctly utilized the PHB at the test location in Fargo, North Dakota. The most significant contribution of this thesis was finding that the current PHB standards in MUTCD are not transferable to the school zone context. For PHBs to be considered a viable option for engineers designing and controlling school crosswalks, it is essential that the MUTCD have school zone specific standards or guidance. The analysis carried out in this research provides insights into how such standards can be established and applied.
Analyses of Highway Project Construction Risks, Performance, and Contingency
(North Dakota State University, 2010) Diab, Mohamed F.
Past studies have highlighted the importance of risk assessment and management in construction projects and transportation industry, and have identified cost and time as the most important risks that transportation professionals want to understand and manage. The main focus of this study is to comprehensively analyze transportation construction risk drivers and identify the correlation of the significant risk drivers with project characteristics, cost growth, schedule growth, and project contingency. This study has adopted 31 relevant and significant programmatic and project-specific risk drivers from different past studies. These risk drivers have been analyzed and evaluated using survey responses from professionals in the context of highway transportation projects. Risk assessments including rating of the encountered risk drivers and their correlation with project characteristics have been carried out within the context of highway construction projects in the United States. Correlations of the construction project performance or risk measures, cost growth percentage, and schedule growth percentage, with the rating values of identified risk drivers values have enabled a better understanding of the impacts of risks and the risk assessment process for highway transportation projects. The impact of significant risk drivers on reported construction cost contingency amounts has also been analyzed. The purpose of this effort was to assess impact of ratings for cost impact, schedule impact, and relative importance of the identified risk drivers on contingency amounts. Predetermined method is the common way to calculate contingency amount in transportation projects. In this study parametric modeling has been used to analyze the relationship between predetermined contingency amounts in transportation projects with perceived risk rating values in order to understand how the expert judgments regarding risk ratings can be used in determination of contingency amounts.
An Investigation of the Kerogen-Mineral Interactions in Green River Oil Shale
(North Dakota State University, 2010) Alstadt, Kristin Nadiene
Green River oil shale contains minerals, kerogen, and bitumen and yields a significant amount of oil upon heating. Kerogen is the insoluble organic remains found in sedimentary materials. It is a precursor to crude oil and is one of the most abundant forms of carbonaceous materials on earth. The richest oil shale deposits in the world are found in the Green River Formation located in the states of Utah, Wyoming and Colorado in the United States with the potential to be a major national resource. Current extraction methods involve heating the shale to high temperatures in order to decompose and evaporate the shale oil. This method is very inefficient due to tremendous energy requirements and is environmentally unfriendly. Thus, the extraction of kerogen is commercially not viable in the United States at this time. My research at North Dakota State University has been focused on understanding how the kerogen is "locked" in the surrounding mineral matrix. The research involves experimental and modeling studies aimed at evaluating the molecular interactions in the oil shale. The focus of my study has been on the in situ chemical composition, mechanical properties, and the physical location of kerogen in Green River oil shale. Fourier Transform Infrared (FTIR) studies have been conducted using the photoacoustic step-scan method to investigate the molecular nature of light and dark colored areas of the oil shale core. This technique provided the means for in situ investigation of kerogenmineral interactions. Results show that light colored oil shale has a high kerogen content with spectra similar to that of isolated kerogen while dark colored oil shale has more mineral components. Kerogen band shifts occurred indicating interactions on the molecular scale between kerogen and the surrounding minerals. Scanning Electron Microscope (SEM) studies were performed in order to obtain information on the size and layout of pores, minerals, and kerogen in the shale. Energy Dispersive Spectroscopy (EDS) performed ort light and dark colored samples indicate that the light colored oil shale contains more kerogen associated with the minerals quartz, clay, and potassium-feldspar. Dark oil shale samples contained kerogen, clay, dolomite, calcite, pyrite, and analcite. SEM images perpendicular to the bedding plane of cross-sectional polished oil shale samples showed orientated layers and elongation consistent with compression over time. The absence of large kerogen regions in SEM images and nanoindentation results suggest that Green River kerogen is on the scale of tens of nanometers and is in close proximity to oil shale minerals. The mechanical properties of kerogen and oil shale minerals were found using nanoindentation techniques. Green River kerogen was found to have an elastic modulus of 9 GPa and hardness of 1 GPa.
Durability of Concrete Members Strengthened with CFRP Sheets under Harsh Environmental Conditions
(North Dakota State University, 2010) Hossain, Md. Mozahid
The deterioration of concrete structures 1s a maJor concern to the infrastructure community. Typical sources of deterioration may include aging,.incrcased service load, and environmental damage. Structural rehabilitation using carbon fiber reinforced polymer (CFRP) sheets has recently attracted attention to the infrastructure community because of the superior strengthening effects in comparison to conventional repair methods. The CFRP sheets may be bonded on the deteriorated concrete structure using bonding agents to enhance load-carrying capacity. The most important consideration in such a strengthening method may be the long term durability under harsh environmental conditions. Furthermore, premature debonding of bonded CFRP sheets may also cause significant losses of the strengthening effects. Although extensive research has been reported on the debonding mechanism of CFRP sheets, there is still lack of understanding on the durability of CFRPs subject to low temperature effects. This thesis presents some major findings of the durability performance of concrete members strengthened with CFRP sheets subjected to harsh environments.
Analyses of Highway Project Construction Risks, Performance, and Contingency
(North Dakota State University, 2010) Mohamed, Fahmy Diab
Past studies have highlighted the importance of risk assessment and management in construction projects and transportation industry, and have identified cost and time as the most important risks that transportation professionals want to understand and manage. The main focus of this study is to comprehensively analyze transportation construction risk drivers and identify the correlation of the significant risk drivers with project characteristics, cost growth, schedule growth, and project contingency. This study has adopted 31 relevant and significant programmatic and project-specific risk drivers from different past studies. These risk drivers have been analyzed and evaluated using survey responses from professionals in the context of highway transportation projects. Risk assessments including rating of the encountered risk drivers and their correlation with project characteristics have been carried out within the context of highway construction projects in the United States. Correlations of the construction project performance or risk measures, cost growth percentage, and schedule growth percentage, with the rating values of identified risk drivers values have enabled a better understanding of the impacts of risks and the risk assessment process for highway transportation projects. The impact of significant risk drivers on reported construction cost contingency amounts has also been analyzed. The purpose of this effort was to assess impact of ratings for cost impact, schedule impact, and relative importance of the identified risk drivers on contingency amounts. Predetermined method is the common way to calculate contingency amount in transportation projects. In this study parametric modeling has been used to analyze the relationship between predetermined contingency amounts in transportation projects with perceived risk rating values in order to understand how the expert judgments regarding risk ratings can be used in determination of contingency amounts.
Comparisons of Energy Dissipation in Structural Devices with Foundation Soil During Seismic Loading
(North Dakota State University, 2010) Saravanathiiban, Duraisamy Soundararajan
The effectiveness of structural energy dissipation mechanisms such as passive energy dissipation devices and base isolation methods used in seismic design depends on their capacity, ductility, energy dissipation, isolation, and self-centering characteristics. Though rocking shallow foundations could also be designed to possess many of these desirable characteristics, current seismic design codes often avoid nonlinear behavior of soil and energy dissipation beneath foundations because of concerns about permanent deformations at foundation level. This thesis compares the effectiveness of energy dissipation in foundation soil with structural energy dissipation devices during seismic loading. Numerical simulations of structures with and without energy dissipation devices were carried out to systematically study the seismic energy dissipation in structural elements and energy dissipation devices. The numerical model was validated using shaking table experimental results on model frame structures with and without energy dissipation devices. The energy dissipation in the structure, drift ratio, and the force and displacement demands on the structure are compared with energy dissipation characteristics of rocking shallow foundations as observed in centrifuge experiments, where shallow foundations were allowed to rock on dry sandy soil stratum during dynamic loading. The comparisons of results clearly indicate that foundation (rocking) energy dissipation mechanism is as efficient as structural passive energy dissipation devices. For the structures with energy dissipating devices, about 70% to 90% of the seismic input energy is dissipated by energy dissipating devices, while foundation rocking dissipates about 30% to 90% of the total seismic input energy in foundation soil (depending on static factor of safety). Inclusion of energy dissipating braces increases the base shear force transmitted to the structure, while normalized base shear forces transmitted to the foundation during rocking are smaller than those of the structures with energy dissipating devices because of the isolation effect of rocking foundations. If properly designed (with reliable capacity and tolerable settlements), adverse effects of foundation rocking can be minimized while taking advantage of the favorable features of foundation rocking, and hence they can be used as efficient and economical seismic energy dissipation mechanisms in buildings and bridges.
Filamentous Growth in Entrapped Microbial Cell Reactor Treating Wastewater
(North Dakota State University, 2010) Sathyaseelan, Vinodgnanadrepan
The overgrowth of filamentous microorganisms in wastewater treatment systems is a common adversary condition leading to foaming, poor sludge settling problems, and reduction in organic removal efficiency. Entrapped microbial cell reactors have been investigated for their uses in wastewater treatment. However, their susceptibility to filamentous growth is not known. The objective of this study is to investigate the filamentous growth and its effect on the treatment performance of an entrapped microbial cell system treating wastewater. A typical activated sludge wastewater treatment system was included for comparative purpose. Both systems were operated at the same operating conditions using synthetic wastewater. Four different hydraulic retention times (HRT) (9, 6, 3, 1.5 hours), three different dissolved oxygen (DO) concentrations (2, 4.5 and 5.7 mg/1), and three different influent chemical oxygen demand (COD) concentrations ( 120, 206 and 300 mg/I) were investigated. Results showed that DO and organic loading rate (COD/HRT) did not have any effect on the organic (soluble COD and soluble biochemical oxygen demand at 5 days) removal efficiencies at high and medium HRT (9 and 6 hours), even when there was excessive filamentous growth in the entrapped microbial cell reactor. The organic removal efficiencies of the activated sludge system dropped for some cases at high and medium HRT because of excessive filamentous overgrowth. At low HRT (3 hours), there was abundant filamentous growth and a drop in the organic removal efficiencies in the entrapped microbial cell reactor. To determine the reason (between HRT and filamentous abundance) for the decreases in organic removal efficiencies by the entrapped microbial cell system at the low HRT, a very low HRT of 1.5 hours was applied. DO and organic loading rate did not affect organic removal efficiencies of the entrapped cell reactor. Reduction of the filamentous microorganisms was attempted by chlorination using sodium hypochlorite. Three different chlorine dosages, I, 0.25 and 0.50 g NaOCl/d, were applied. The dosage of 0.25 g NaOCl/d was found to be very effective in controlling the filamentous overgrowth in the entrapped microbial cell reactor. The reduction of filamentous organisms by chlorination did not result in improved organic removal efficiencies, suggesting that the very low HRT rather than the abundance of filamentous organisms was responsible for the poorer performance of the reactor. A cell morphology and organelle analysis indicated Sphaerotilus natans as the most frequently observed filamentous microorganism in the entrapped microbial cell reactor. A thick layer of biofilm was also observed on the entrapment matrix. The biofilm did not affect the performances of the reactor. These results suggested that the entrapped microbial cell reactor is subjected to filamentous overgrowth, but it has no effect on the performances of the reactor.
Modeling and Analysis of Impacts of Right-Tum Lane Lengths
(North Dakota State University, 2010) Chevuri, Pavan Kumar
Tum lanes have been studied for several decades, with focus being on left-tum lanes and for urban areas. The need for right-tum lanes has been studied using the impact of such tum lanes on both safety and operational efficiency. However, the impacts of different right-tum lane lengths have not been studied well. The determinations of righttum lane lengths have been based primarily on the deceleration of the right-turning vehicles, which happens to be one of the many factors that should influence such decisions. In this study the impacts of the right-tum lanes on two-lane roads with no controls on major roads have been modeled and analyzed. In particular, the impacts on the space mean speed and the delays have been studied using both the analysis of field data from several intersections around Minnesota and the analysis of the results from simulation models developed using CORridor SIMulation (CORSIM®)
Quantification of the Influences of Subsurface Uncertainties on Seismic Behavior of Shallow Foundations
(North Dakota State University, 2011) Kayser, Mohammad Feroz Ahmed
The properties of geomaterials are uncertain. These uncertainties not only affect the dynamic behavior of the geomaterials, but also significantly influence the complex nonlinear dynamics between the soil, foundation, and the structure (dynamic soilfoundation- structure interaction - SFSI). However, current civil engineering approach in incorporating the effects of SFSI on the seismic behavior of structures is still largely deterministic without considering uncertain geomaterial properties. The objectives of this research are to characterize the uncertainties in soil properties m a probabilistic framework and to quantify their effects on dynamic soil-foundation system behavior during seismic loading. The research methodology includes systematic propagation of uncertainties in soil properties through soil-foundation interface to the dynamic behavior of the structure during seismic loading. A recently developed Contact Interface Model (CIM), to model the soil-foundation system behavior during seismic loading, has been used in numerical simulations. To study the sensitivity of the response of the soil-foundation system to the random input parameters, probabilistic analyses have been carried out using Tornado Diagram analysis, Spider Plot analysis, First Order Second Moment (FOSM) analysis, and small scale Monte-Carlo simulations. Results obtained from the probabilistic numerical simulations indicate that ultimate moment capacity of the soil-foundation system during seismic loading is more sensitive to the uncertainty in the applied vertical load on the foundation than the uncertainties in soil properties. Since the uncertainty in applied vertical load is considerably smaller than the uncertainties in soil properties, the ultimate moment capacity of shallow foundation is predictable with reasonable accuracy. Energy dissipation beneath the foundation mainly depends on the applied vertical load and initial vertical stiffness of the foundation, while initial vertical stiffness of the foundation and rebounding ratio were found to contribute the most to the settlement of the foundation. The rotation of the foundation is more sensitive to the shaking intensity than uncertainties in soil properties.
Bounding Surface Approach to the Fatigue Modeling of Engineering Materials with Applications to Woven Fabric Composites and Concrete
(North Dakota State University, 2011) Wen, Chao
It has been known that the nucleation and growth of cracks and defects dominate the fatigue damage process in brittle or quasi-brittle materials, such as woven fabric composites and concrete. The behaviors of these materials under multiaxial tensile or compression fatigue loading conditions are quite complex, necessitating a unified approach based on principles of mechanics and thermodynamics that offers good predictive capabilities while maintaining simplicity for robust engineering calculations. A unified approach has been proposed in this dissertation to simulate the change of mechanical properties of the woven fabric composite and steel fiber reinforced concrete under uniaxial and biaxial fatigue loading. The boundary surface theory is used to describe the effect of biaxial fatigue loading. A fourth-order response tensor is used to reflect the high directionality of the damage development, and a second-order response tensor is used to describe the evolution of inelastic deformation due to damage. A direction function is used to capture the strength anisotropic property of the woven fabric composite. The comparisons between model prediction results and experimental data show the good prediction capability of models proposed in this dissertation.
Evaluating the Effects of Rail Preemption Strategies on Highway Safety and Operations
(North Dakota State University, 2011) Bratlien, Andrew Lee
Previous research related to signal preemption near highway-rail grade crossings has emphasized safety considerations, which are paramount due to the severity of potential train-vehicle collisions. The purpose of this research was to quantify the safety and efficiency implications of several common preemption strategies using the conditions in a small urban context. The research evaluates several important characteristics of rail preemption, including track clearance time, advance preempt time, and dwell cycle strategy, particularly with regard to surface street operational efficiency, that current traffic engineering practice do not adequately address. The context and preemption strategies were modeled using simulation software VISSIM. The results identified two separate and potentially serious safety issues related to the interaction of advance preempt time, track clearance time, and existence of four-quadrant gates at railroad crossing. In addition, the research also highlighted the negative effect of excessive track clearance time and dwell cycle on adjacent surface street operations.
Fate and Transformation of a Conjugated Natural Hormone 17β-Estradiol-3-Glucuronide in Soil-Water Systems
(North Dakota State University, 2011) Shrestha, Suman Lal
The objectives of the study were to investigate the sorption and degradation of a glucuronide conjugated natural hormone, 17β-estradio1-3-glucuronide (E2-3G), and its estrogenic metabolites in soil-water systems. Radiolabeled E2-3G was first synthesized in the laboratory. Soil-water batch experiments were then conducted using natural and sterilized topsoil (0-6 cm) and subsoil (18-24 cm) with the radiolabeled E2-3G to investigate the effects of soil organic matter content and microbial activity. The aqueous dissipation of 14C in the batch experiments followed a biphasic pattern with an initial rapid dissipation phase followed by a second slower phase. Significant differences in total aqueous 14C dissipation were observed for the different initial concentrations for both soils, with greater persistence of intact E2-3G at higher initial concentrations.
Time-dependent Behavior of Various FRP Composites for Structural Applications
(North Dakota State University, 2011) Khan, Md. Fuad Hassan
This thesis represents the long-term behavior of fiber reinforced polymer (FRP) materials for structural applications. FRP composites consist of high-strength fibers embedded in an epoxy resin. The long-term investigations include i) pultruded glass FRP (GFRP) beams subjected to sustained loads and cold temperature and ii) reinforced concrete beams strengthened with near-surface mounted (NSM) carbon FRP (CFRP) strips. For the first phase, test parameters include the variation of sustained intensities and temperature. The flexural behavior of the long-term beams is studied through a combined experimental and numerical approach, including load-carrying capacity, failure mode, creep response, and material degradation. Some material parameters that are crucial for practical applications are suggested using a regression analysis. A finite element model is developed to predict the behavior of GFRP beams. An analytical model is also proposed to estimate the long-term behavior of GFRP composites for structural applications. For the second phase, test parameters include the variation of sustained intensities, CFRP strengthening schemes and bonding agents. The short-term beams are loaded both monotonically and cyclically whereas the long-term beams are loaded only monotonically. The flexural behavior of all beams is studied through an experimental investigation, including load-carrying capacity, failure mode, creep response, and material degradation.
Experimental Studies on Infiltration/Soil-Water Movement Processes and Green-AMPT Modeling
(North Dakota State University, 2011) Sande, Leif Andrew
Experimental studies on infiltration/soil-water movement processes are vital to better understanding movement of soil-water in the vadose zone. The objective of this experimental research was to investigate infiltration/soil-water movement processes utilizing laboratory experiments and computer modeling. Small scale laboratory soil box infiltration experiments were conducted and utilized for the improved parameterization of the Green-Ampt (GA) saturated moisture content parameter to produce an effective moisture content parameter (Be) for utilization in a modified GA model. By incorporating ⊖e values into GA modeling, modeling results showed greatly improved wetting front prediction across different soil conditions. A new soil packing method was proposed for replicating complex microtopographical surfaces with uniform bulk densities in laboratory soil box experiments which proved efficient and effective at accomplishing both objectives. A rainfall simulator and an instantaneous-profile laser scanner were used to simulate rainfall and quantify surface microtopography for experiments. The results clearly show the effect of microtopography on infiltration and soil-water movement characteristics. This offers valuable insight into infiltration/soil-water movement processes as affected by different soil and surface microtopographic conditions.
Fate and Characteristics of Dissolved Organic Nitrogen through Wastewater Treatment Systems
(North Dakota State University, 2012) Simsek, Halis
Dissolved organic nitrogen (DON) represents a significant portion (25-80%) of total dissolved nitrogen in the final effluent of wastewater treatment plants (WWTPs). DON in treated wastewater, once degraded, causes oxygen depletion and/or eutrophication in receiving waters and should be reduced prior to discharge. Biodegradability, bioavailability, and photodegradability are important characteristics of wastewater derived DON and are subjects of research in this dissertation. Four research tasks were performed. In the first task, laboratory-scale chemostat experiments were conducted to examine whether solids retention time (SRT) could be used to control DON and biodegradable DON (BDON) in treated wastewater. Nine different SRTs from 0.3 to 13 were studied. There was no correlation between effluent DON and SRTs. However, BDONs at SRTs of 0.3 to 4 days were comparable and had a decreasing trend with SRTs after that. These results indicate the benefit of high SRTs in term of producing effluent with less BDON. The second task was a comprehensive year-round data collection to study the fate of DON and BDON through the treatment train of a trickling filter (TF) WWTP. The plant removed substantial amounts of DON (62%) and BDON (76%) mainly through the biological process. However, the discharged concentrations in the effluent were still high enough to be critical for a stringent total nitrogen discharge limit (below 5 mg-N/L). Evolution of bioavailable DON (ABDON) along the treatment trains of activated sludge (AS) and TF WWTPs and relationship between ABDON and BDON were examined in the third task. ABDON exerted from a combination of bacteria and algae inocula was higher than algae inoculated ABDON and bacteria inoculated BDON suggesting the use of algae as a treatment organism along with bacteria to minimize effluent DON. The TF and AS WWTPs removed 88% and 64% of ABDON, respectively. In the last task, photodegradable DON (PDON) in primary wastewater and final effluent from TF and AS WWTPs was studied. PDON and BDON fractions of DON data in the final effluent of TF and AS WWTP samples elucidate that photodegradation is as critically important as biodegradation when mineralization of effluent DON is a concern in receiving waters.
Alginate Encapsulated Nanoparticle-Microorganism System for Trichloroethylene Remediation
(North Dakota State University, 2012) Shanbhogue, Sai Sharanya
Nanoscale zero-valent iron (NZVI) particles were encapsulated in calcium alginate capsules for application in environmental remediation. TCE degradation rates for encapsulated and bare NZVI were similar indicating no adverse effects of encapsulation on degradation kinetics. Microorganisms were separately encapsulated and used along with encapsulated NZVI and co-encapsulated in calcium alginate capsules. Batch experiments were performed to test the efficacy of the combined iron-Pseudomonas sp. (PpF1) system. The combined system removed 100% TCE over the first three hours of the experiment followed by 70% TCE removal post TCE re-dosing. Complete reduction of TCE was achieved by NZVI between 0-3 h and the second phase of treatment (3-36 h) was mostly achieved by microorganisms. Experiments conducted with co-encapsulated NZVI-D.BAV1 achieved 100% TCE removal. During the first three hours of the experiment 100% TCE removal was achieved by NZVI, and 100% removal was achieved post re-dosing where D.BAV1 accomplished the treatment.
A Comparative Study of Nitrification in Fargo and Moorhead Distribution Networks
(North Dakota State University, 2012) Portlock, Daniel
Nitrification in water distribution networks has become a growing concern for water supplies in the United States. The use of chloramines as a disinfectant in distribution pipe networks has become increasingly popular to reduce the disinfectant byproducts that are formed with free chlorine. In chloraminated systems there is potential for nitrification to occur because it reduces chloramine residuals. As chloramines decompose in the network, ammonia is released. Nitrifiers oxidize ammonia into nitrites, which react with chloramines resulting in its further reduction. As this cycle continues, chloramines will be consumed faster in the network, causing regrowth of heterotrophic bacteria. A study was conducted to compare the Fargo and Moorhead distribution networks for the occurrence of nitrification and their potential to deteriorate water quality. Each distribution network was analyzed independently for variations in operational conditions and water quality parameters that can serve as indications of nitrification in a distribution network.
Influence of Molecular Interactions on Elastic Properties and Oxygen Diffusion in PolyButylene Terephthalate Polymer: A Molecular Dynamics Study
(North Dakota State University, 2012) Raviprasad, Muniyamuthu
In most barrier applications, both mechanical and diffusion properties of the material are important. In this thesis the evaluation of molecular mechanisms responsible for the enhanced elastic properties of Polymer Clay Nanocomposites (PCNs) and the molecular mechanisms of Oxygen diffusion in PolyButylene Terephthalate polymer are presented. Interaction energy between PCN constituents, conformational changes of polymer, interaction energy between Oxygen molecule and polymer, rate of Oxygen and Oxygen diffusion coefficient are evaluated. Molecular simulation studies of PolyButylene Terephthalate (PBT) clay nanocomposite and Nylon6 clay nanocomposite show that a higher crystallinity polymer such as PBT would require higher attractive and repulsive interactions with organic modifier in order to make significant change in the crystallinity of PBT in the nanocomposite and in turn enhance the elastic modulus and hardness. Molecular interactions energy between Oxygen molecule and polymer, change in polymer conformation caused by thermal energy assist the Oxygen molecule to diffuse through polymer.
Safety Effectiveness and Safety-Based Volume Warrants of Right-Turn Lanes at Unsignalized Intersections and Driveways on Two-Lane Roadways
(North Dakota State University, 2012) Ale, Gom Bahadur
Disagreements regarding to what degree right-turn lanes improve or worsen the safety of intersections and driveways provided the motivation and the need for this study. The objectives of this study were to: a) carry out an in-depth study to determine the safety impacts of right-turn movements in different contexts, and b) develop safety-based volume warrants for right-turn lanes if safety indeed improves. Lack of adequate study on the applicability of past warrants and guidelines for the specific context of right-turn movements made from major uncontrolled approaches at unsignalized intersections, and particularly driveways, on two-lane roadways provided the scope for this study. Five-year historical data of statewide traffic crashes reported on Minnesota’s twolane trunk highways were analyzed using binary/multinomial logistic regressions. Conflicts due to right turns were analyzed by fitting least squares conflict prediction models based on the data obtained from field surveys and traffic simulations. The safety impacts of rightturn lanes were determined through crash-conflict relationships, crash injury severity, and crash and construction costs. The study found that the probabilities of right-turn movement related crash ranged from 1.6 to 17.2% at intersections and from 7.8 to 38.7% at driveways. Rear-end, samedirection- sideswipe, right-angle and right-turn crash types constituted 96% of right-turn movement related crashes. Rear-end crash probabilities varied from 13.7 to 46.4% at approaches with right-turn lanes and from 37.9 to 76.9% otherwise. The ratios of rearend/ same-direction-sideswipe crashes to conflicts were 0.759 x 10^6 at approaches with right-turn lanes and 1.547 x 10^6 otherwise. Overall, right-turn lanes reduced right-turn movement related crash occurrences and conflicts by 85% and 80%, respectively. Right-turn lanes also reduced crash injury severity, hence, reducing the economic cost by 26%. Safety benefits, in dollars, realized with the use of right-turn lanes at driveways were 29% and 7% higher compared to those at intersections at low and high speed conditions respectively for similar traffic conditions. Depending on roadway conditions, interest rate and construction costs, the safety-based volume thresholds ranged from 3 to 200 right turns per hour during the design hour at intersection approaches, and from 2 to 175 right turns at driveway approaches.
Characterization of Surface Microtopography and Determination of Hydrotopographic Properties
(North Dakota State University, 2012) Chi, Yaping
Spatial characterization of surface microtopography is important in understanding the overland flow generation and the spatial distribution of surface runoff. In this study, fractal parameters (i.e., fractal dimension D and crossover length l) and three hydrotopographic parameters, random roughness (RR) index, maximum depression storage (MDS), and the number of connected areas (NCA), have been applied to characterize the spatial complexity of microtopography. Clear and meaningful relationships have been established between these parameters. The RR was calculated as the standard deviation of the processed elevation, and the fractal parameters were calculated with the semivariogram method. The puddle delineation program was applied in this study to spatially delineate soil surface and to accurately determine MDS and NCA. It has been found that fractal parameters can better characterize surface microtopography. More importantly, fractal and anisotropic analyses can help to better understand the overland flow generation process.

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