Civil & Environmental Engineering
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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.Item AN INTEGRATED TRAFFIC CONTROL SYSTEM FOR FREEWAY CORRIDORS UNDER NON-RECURRENT CONGESTION(2009) Liu, Yue; Chang, Gang-Len; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This research has focused on developing an advanced dynamic corridor traffic control system that can assist responsible traffic professionals in generating effective control strategies for contending with non-recurrent congestion that often concurrently plagues both the freeway and arterial systems. The developed system features its hierarchical operating structure that consists of an integrated-level control and a local-level module for bottleneck management. The primary function of the integrated-level control is to maximize the capacity utilization of the entire corridor under incident conditions with concurrently implemented strategies over dynamically computed windows, including diversion control at critical off-ramps, on-ramp metering, and optimal arterial signal timings. The system development process starts with design of a set of innovative network formulations that can accurately and efficiently capture the operational characteristics of traffic flows in the entire corridor optimization process. Grounded on the proposed formulations for network flows, the second part of the system development process is to construct two integrated control models, where the base model is designed for a single-segment detour operation and the extended model is designated for general network applications. To efficiently explore the control effectiveness under different policy priorities between the target freeway and available detour routes, this study has further proposed a multi-objective control process for best managing the complex traffic conditions during incident operations. Due to the nonlinear nature of the proposed formulations and the concerns of computing efficiency, this study has also developed a GA-based heuristic along with a successive optimization process that can yield sufficiently reliable solutions for operating the proposed system in a real-time traffic environment. To evaluate the effectiveness and efficiency of the developed system, this study has conducted extensive numerical experiments with real-world cases. The experimental results have demonstrated that with the information generated from the proposed models, the responsible agency can effectively implement control strategies in a timely manner at all control points to substantially improve the efficiency of the corridor control operations. In view of potential spillback blockage due to detour operations, this study has further developed a local-level bottleneck management module with enhanced arterial flow formulations that can fully capture the complex interrelations between the overflow in each lane group and its impact on the neighboring lanes. As a supplemental component for corridor control, this module has been integrated with the optimization model to fine-tune the arterial signal timings and to prevent the queue spillback or blockages at off-ramps and intersections. The results of extensive numerical experiments have shown that the supplemental module is quite effective in producing local control strategies that can prevent the formation of intersection bottlenecks in the local arterial.Item ANALYSIS OF ACTIVITY CHOICE: THE ROLE OF ACTIVITY ATTRIBUTES AND INDIVIDUAL SCHEDULES(2009) Akar, Gulsah; Clifton, Kelly J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Activity-based approaches have taken hold in transportation research over the last several decades. The foundation of the activity-based approach is to view travel as a result of our activity choices and scheduling decisions. Therefore, better understanding of activity choice, planning time horizons, and activity attributes will lead to more accurate demand forecasts. This dissertation extends the current activity choice modeling framework by incorporating the characteristics of the individuals' schedules, planning time horizons and focusing on the salient attributes of the activities. This study consists of three parts which are linked to one another by their conceptual and empirical findings. The first part identifies the determinants of the planning time horizons - defined as when people decide about performing their activities. Several household and individual characteristics, and activity attributes are tested for their association with planning times. The activity attributes which have significant impacts on the planning time horizons of the activities are used in the second part for generating new activity groups. The second part clusters activities based on their salient attributes, such as duration, frequency, number of involved people and flexibilities, rather than their functional types (work, leisure, household obligations, etc.) and creates activity groups such as "long, infrequent, personally committed activities", "quick, spatially fixed, temporally flexible activities" etc. The activity groups generated in this part inform the activity choice modeling structure developed in the third part. The main analytical techniques used in this research are the Principal Components Analysis (PCA) and discrete choice models. PCA is used to define the new activity groups. The analysis of the planning time horizons and activity choice are performed by mixed logit models. The model results reveal the significant relationships between socio-demographics, temporal characteristics, travel, and characteristics of the schedules on activity choice. The findings of these models could be integrated in the activity choice modules of the existing activity-travel simulation models by either applying the comprehensive model (which may face limitations due to the availability of data) or integrating the findings of the models in the decision rules.