Civil & Environmental Engineering
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Item SCALING OF SURFACE ENERGY FLUXES USING REMOTELY SENSED DATA(2001) French, Andrew Nichols; Brubaker, Kaye L.; Civil and Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Accurate estimates of evapotranspiration (ET) across multiple terrains would greatly ease challenges faced by hydrologists, climate modelers , and agronomists as they attempt to apply theoretical models to real-world situations. One ET estimation approach uses an energy balance model to interpret a combination of meteorological observations taken at the surface and data captured by remote sensors. However, results of this approach have not been accurate because of poor understanding of the relationship between surface energy flux and land cover heterogeneity, combined with limits in available resolution of remote sensors. The purpose of this study was to determine how land cover and image resolution affect ET estimates. Using remotely sensed data collected over El Reno, Oklahoma, during four days in June and July 1997, scale effects on the estimation of spatially distributed ET were investigated. Instantaneous estimates of latent and sensible heat flux were calculated using a two-source surface energy balance model driven by thermal infrared, visible- near infrared, and meteorological data. The heat flux estimates were verified by comparison to independent eddy-covariance observations. Outcomes of observations taken at coarser resolutions were simulated by aggregating remote sensor data and estimated surface energy balance components from the finest sensor resolution (12 meter) to hypothetical resolutions as coarse as one kilometer. Estimated surface energy flux components were found to be significantly dependent on observation scale. For example, average evaporative fraction varied from 0.79, using 12-m resolution data, to 0.93 , using 1-km resolution data. Resolution effects upon flux estimates were related to a measure of landscape heterogeneity known as operational scale, reflecting the size of dominant landscape features. Energy flux estimates based on data at resolutions less than 100 m and much greater than 400 m showed a scale dependent bias. But estimates derived from data taken at about 400-m resolution (the operational scale at E l Reno) were susceptible to large error due to mixing of surface types. The El Reno experiments show that accurate instantaneous estimates of ET require precise image alignment and image resolutions finer than landscape operational scale. These findings are valuable for the design of sensors and experiments to quantify spatially-varying hydrologic processes.Item Using MODIS Satellite Images to Confirm Distributed Snowmelt Model Results in a Small Arctic Watershed(2009) Choy, David F.; Brubaker, Kaye; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Environmental analysts face the problem of obtaining distributed measurements to evaluate the performance of models with increasingly small spatiotemporal resolution. While U.S. government agencies readily provide both measurement products and data tools for the study of global change occurring over entire seasons and across continental areas, analysts need access to the low-level data that provides the basis for global products. Finally, analysts need to consider sensor errors inherent in low-level products that are accounted for in global, composite products. Hydrologists using tools for managing low-level snow swath measurements, in particular, must consider how measurements are affected by sensor errors like snow-cloud confusion and sensor errors due to low ground illumination at night. This thesis aims to explore the use of remotely sensed snow maps to confirm a time series of model maps. Specifically, snow covered area (SCA) measurements remotely sensed by the National Aeronautics and Space Administration (NASA) are used to confirm SCA predictions modeled by the United States Agriculture Department (USDA). The measurements come from the two Moderate Resolution Imaging Spectroradiometer (MODIS) sensors aboard near-polar, sun-synchronous satellites named Aqua and Terra. The USDA calls the model TOPMODEL-Based Land-Atmosphere Transfer Scheme (TOPLATS). The Upper Kuparuk River Watershed (UKRW) on the North Slope of Alaska acts as the case study location. To meet the map-comparison goal, the Kappa statistic, Kappa statistic variants, and probability density functions expressing measurement uncertainty in discrete scenes all evaluate the ability of MODIS measurements to confirm the accuracy of TOPLATS model maps. Data management objectives to make measured data accessible and comparable to the model output comprise a supporting goal. Results show that individual composite statistics, like the proportion of agreement between two maps, can easily obscure spatiotemporally distributed confirmation information without additional statistics and side-by-side images of measurement maps and model maps. These tools show some promise for using MODIS to confirm model predictions of snowmelt that occur across less than 150 km2 and less than a few days, however, clouds and malfunctioning sensors limit such use.Item Modeling of Consolidation by Household for Emergency Evacuation Events(2009) Liu, Ke; Lovell, David J; Chang, Peter C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Evacuation studies have grown in importance over the years as a number of recent emergencies, natural and man-made, have raised the general level of awareness about public responses to the threat or actual occurrence of disasters. An accurate prediction of the rates of evacuation and estimate of the time required to clear a risk area are important planning tools that can mitigate the consequences of an emergency situation. Traditional evacuation models are predicated on the assumption that everyone would seek the quickest or shortest route to safety, given a life-threatening situation. Observations, however, show that a large percentage of the population does not seek the quickest route to safety. Parents may move toward dangers to pick up their children from schools. Persons at work may go back home to pick up dependent family members, pets, and personal effects before evacuation begins in earnest. Incorrect assumptions of evacuee behaviors could lead to measures that negatively impact the traffic flow during evacuation. One effective method to evaluate different evacuation strategies is the use of simulation. Most established simulation models, however, are not built to take the underlying drivers' social behavior into considerations. In this study, we develop a computerized tool for modeling evacuation dynamics with household consolidation, and then incorporate it into a traffic-simulation software platform. This tool will allow a percentage of the population to consolidate as a family before they evacuate. After that, a study is conducted to explore the consolidation by household in a network under various demand levels. A mathematical model is presented to capture the underlying relationships among the network components. Next, the traffic volumes entering and leaving the network are investigated to highlight some recommendations about the appropriate implementation of contraflow or staged evacuation strategies. To help decision makers have a better understanding of the evacuation traffic patterns, this study also examined the influences from spatio-temporal information such as the information dissemination delay, the evacuees' preparedness time, the numbers and locations of shelters in a network, and demographical information like the number of vehicles in a family. The proposed research will allow planners to study more realistically the effects of evacuation strategies. The results of studying such household by consolidation behavior are (1) evacuation times are significantly longer compared to the assumption of evacuees taking the shortest route away from danger in low/average demands; (2) with heavy demand, low consolidation rates can produce long evacuation times due to the rapid development of congestion at the network exits; (3) with heavy demand, high consolidation rates could delay the turning point to reverse the inbound lanes to outbound in a contraflow operation; (4) the sequencing of converting inbound lanes to outbound in a contraflow operation should start at the outermost links and work inward, due to extra bi-directional traffic on the network engaged in consolidation activities; (5) information delays and evacuees' preparedness as a family, coupled with the family consolidation behavior, are important parameters to the evacuation performance; (6) information on demographics and geography also has an important impact on the network evacuation efficiency and evacuees' social behaviors; more specifically, the evacuation performance is very sensitive to the number of shelters in the network.Item Crushed Returned Concrete Aggregate in New Concrete: Characterization, Performance, Modeling, Specification, and Application(2009) Kim, Haejin; Goulias, Dimitrios; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Every year roughly 2% to 10% of the estimated 455 million cubic yards of ready mixed concrete produced in the USA (est. 2006) is returned to the concrete plant. The crushed returned concrete aggregate (CCA) is obtained from crushing the returned concrete that was discharged at the concrete pant and left for a period of time before crushing. It is estimated that about 60% of all returned concrete is managed with this manner by the concrete plant according to the national ready mixed concrete association report. But the reuse of the returned concrete aggregate is very much limited so that most of the returned concrete aggregate has been diverted to the landfill. The main obstacle to limit the use of the returned concrete aggregate is the current type of prescriptive specifications by controlling the concrete composition, which limits the ability to optimize concrete mixtures for performance. The CCA aggregate has useful aggregate properties among which it is free of any contamination. Thus, CCA aggregate is distinguished from other recycled concrete aggregate (RCA) that comes out of existing old structures with high contamination from many years of exposure during the service life. The objective of this research was to develop technical data that will support the use of the CCA aggregates from the returned concrete by the ready mixed concrete industry. Three CCA aggregates at three strength levels were characterized. Thereafter, the virgin coarse/fine aggregates and the three CCA aggregates were used with various amounts to prepare concrete mixtures so as to investigate the effect on the fresh and harden concrete properties. The second objective of this research was to develop the performance models of harden concrete properties. The harden concrete properties of a selected number of mixtures containing CCA aggregates were used for the modeling of compressive strength, drying shrinkage, elastic modulus, and rapid chloride ion penetrability. This analysis was instrumental for a better understanding of how the CCA aggregates affect the harden concrete properties. The fine CCA aggregates were further investigated for their potential use as internal curing agent due to their unique aggregate properties (i.e. low specific gravity and high water absorption capacity). Those two properties are crucial factors for the internal curing. The fine CCA aggregates were used with mortar mixtures to evaluate the strength and autogenous shrinkage behavior along with the lightweight fine aggregate. This new approach can promote the use of CCA aggregate in a specialized application. Another objective of this study was to demonstrate the advantages of using a performance based specification. An example of an experimental case study was used for both conventional and CCA based concrete for comparing performance and prescriptive specifications.Item Behavior and Analysis of an Instrumented Slab Bridge(2009) Jeong, Sungki; Fu, Chung C.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Because of quick construction and cost effectiveness, adjacent precast, prestressed box girder bridges have been used nowadays more often for short-span bridges, and the standardization of this modular bridge is highly desired. Maryland intends to revise its current practice of using tie-rods for the transverse post-tensioning in slab bridge design. The new design of using high strength rods will provide a more tightly integrated modular slab bridge system with higher post-tensioning forces. With the new design, the Maryland State Highway Administration is highly interested in the performance of the new design, especially compared with the old design. This thesis presents the procedure of test, live load test results and analysis results in association with the finite-element model simulated in a newly-built bridge.Item DETERMINING THE RELATIONSHIPS AMONG AIRPORT OPERATIONAL PERFORMANCE AREAS AND OTHER AIRPORT CHARACTERISTICS(2009) Chan, Kennis Yuen Man; Lovell, David J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, a methodology is proposed to investigate pair-wise relationships between different types of airport operational performance variables. The methodology represents a fundamental contribution for comparing airport performance between different air traffic management systems. Considerable attention is paid to analyzing the most appropriate techniques in an effort to produce the most reliable results. Additionally, a method to display the results in a simple and clear way is also suggested to allow users to understand the results visually. The key variables obtained from the proposed methodology not only serve as building blocks for developing models to answer a variety of air traffic questions, which allow policy makers to make decisions on allocating resources wisely, but also can be used as an evaluation tool to assist the FAA in selecting candidate projects.Item SPATIAL MODELING AND UNIT HYDROGRAPH DEVELOPMENT WITH RADAR RAINFALL(2009) Rew, Stephanie Nicole; McCuen, Richard H.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Most hydrologic models use point rainfall data. Point data do not account for spatial characteristics of a storm. This research investigated the benefits of spatially- and temporally-varying rainfall data. Semivariogram analyses were made to assess the importance of the following storm characteristics: size, shape, type, and velocity. Rainfall and flow gage data from the aridlands Walnut Gulch Watershed and regional data were used. A model was developed to estimate transmission losses (TL) using hydrograph routing (temporally-varying data), then a procedure was developed to use radar rainfall data (spatially-varying data) to develop unit hydrographs (UH). Exponentially shaped UHs resulted from TLs. UHs developed from radar data agreed closely with Thiessen-averaged UHs developed from rain gage data, indicating that radar UHs better represented the overall watershed processes than a UH based on a single rain gage. Therefore, accurate UHs can be developed from radar data.Item LINEAR AND NON-LINEAR FREQUENCY DOMAIN TECHNIQUES FOR PROCESSING IMPACT ECHO SIGNALS TO EVALUATE DISTRIBUTED DAMAGE IN CONCRETE.(2009) McMorris, Nicolas A.; Amde, Amde M; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The condition evaluation of in-situ concrete with non-destructive testing is difficult at best. The concrete deterioration processes of alkali-silica reaction (ASR), delayed ettringite formation (DEF) and freeze-thaw cycles all produce distributed damage in the form of micro-cracking which results in loss of strength or stiffness. Presently, a suitable field applicable method for determining the degree of micro-cracking does not exist. The impact echo test is potentially the best candidate if improvements can be made in the signal processing techniques which are crucial for accurately interpreting the data retrieved from concrete with distributed damage. In this research, two batches of concrete specimens were prepared in accordance with standard procedures. A portion of each batch was subjected to either the Modified Duggan cycle or to Freeze Thaw cycles, both proven methods of inducing DEF and micro-cracking respectively. Curing techniques and materials were also chosen to accelerate distributed damage in the concrete specimens. In addition to the impact echo, a number of secondary tests were employed to monitor the progress of distributed damage in the concrete specimens. Previous research efforts utilizing the impact echo method have attempted to characterize damage in terms of P-wave attenuation or pulse velocity. This involves signal processing in the time domain. These are inherently linear dynamics methods whereas the development of micro-cracks in concrete, an inhomogeneous material, gives rise to non-linear dynamics. Non-linear approaches to signal processing in the frequency domain are proposed herein. One involves calculating the deviation of the peak of the response spectrum from the shape of an ideal Lorentzian function model. The other calculates the second order non-linear harmonic coefficient. The results showed that the potassium content, the curing methods and the Duggan and Freeze Thaw cycles had the desired effect of inducing distributed damage. The results of the signal processing of the impact echo data yielded more reasonable results for the specimens subjected to Freeze Thaw testing than for the specimens subjected to the Duggan Cycle. The results of the Freeze Thaw specimens suggest that the non-linear analysis of impact echo signals is capable of accurately quantifying distributed damage in concrete.Item The Effect of Hydrologic Model and Data Complexity on Water Quantity and Quality Prediction Accuracy(2008) Gilroy, Kristin Leigh; McCuen, Richard H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrologic modeling is central to the solution of many flooding and water quality issues. As the complexity of these issues increases, model complexity increases. The purpose of this research was to determine the effects of model and data complexity on hydrologic model prediction accuracy. A complex hydrologic model was developed and then simplified based on structural complexity and the change in accuracy was assessed. Analyses of data complexity were also conducted. The results showed that complex models containing excessive low sensitivity parameters did not significantly improve prediction accuracy. However, a lack of complete representation of the physical processes of the hydrologic cycle did affect prediction accuracy. Data analyses revealed that misalignments between rainfall and runoff gauges may cause poor prediction of peaks and grab samples may adequately represent the mean value but not the distribution of a population. Guidelines were developed to improve future development and application of hydrologic models.Item INCREASING DURABILITY OF HOT MIX ASPHALT PAVEMENTS DESIGNED WITH THE SUPERPAVE SYSTEM(2009) Karimi, Sahand Sasha; Goulias, Dimitrios G; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the implementation of the Superpave mix design method, state highway agencies have experienced significant problems in durability of Hot Mix Asphalt mixtures due to lower binder content. To get a better understanding of the HMA mix production and the current specifications used by MSHA, the following were examined: i) differences in HMA properties that have been observed between samples taken at the plant (QC) vs. behind the paver (QA), ii)possibility of defining a transfer function between QA and QC data and iii) the potential risk to both the agency and the contractors using simulation analysis and based on the current specifications and pay factor equations. For this purpose a simulation tool was developed. The F and t tests showed that the QA and QC are two different populations and cannot be related. The simulation analysis illustrated that the correlation among mixture parameters doesn't affect the long run average pay factor. In addition it was concluded that the newly adopted pay equations are fairly rewarding and penalizing the contractors for mixtures, but the density pay equation needs modification.