Civil & Environmental Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/2221
Browse
163 results
Search Results
Item Design and Analysis of Vehicle Sharing Programs: A Systems Approach(2010) Nair, Rahul; Miller-Hooks, Elise D; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Transit, touted as a solution to urban mobility problems, cannot match the addictive flexibility of the automobile. 86% of all trips in the U.S. are in personal vehicles. A more recent approach to reduce automobile dependence is through the use of Vehicle Sharing Programs (VSPs). A VSP involves a fleet of vehicles located strategically at stations across the transportation network. In its most flexible form, users are free to check out vehicles at any station and return the vehicle at a station close to their destination. Vehicle fleets are comprised of bicycles, cars or electric vehicles. Such systems offer innovative solutions to the larger mobility problem and can have positive impacts on the transportation system as a whole by reducing urban congestion. This dissertation employs a network modeling framework to quantitatively design and operate VSPs. At the strategic level, the problem of determining the optimal VSP configuration is studied. A bilevel optimization model and associated solution methods are developed and implemented for a large-scale case study in Washington D.C. The model explicitly considers the intermodalism, and views the VSP as a `last-mile' connection of an existing transit network. At the operational level, by transferring control of vehicles to the user for improved system flexibility, exceptional logistical challenges are placed on operators who must ensure adequate vehicle stock (and parking slots) at each station to service all demand. Since demand in the short-term can be asymmetric (flow from one station to another is seldom equal to flow in the opposing direction), service providers need to redistribute vehicles to correct this imbalance. A chance-constrained program is developed that generates least-cost redistribution plans such that most demand in the near future is met. Since the program has a non-convex feasible region, two methods for its solution are developed. The model is applied to a real-world car-sharing system in Singapore where the value of accounting for inherent stochasticities is demonstrated. The framework is used to characterize the efficiency of Velib, a large-scale bicycle sharing system in Paris, France.Item A NEW APPROCH TO EVALUATING THE EFFECT OF WATERSHED STORAGE ON FLOOD SKEW(2010) Habete, Daniel; McCuen, Richard H; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Estimates of flood skew are inaccurate and the inaccuracy influences flood discharge estimates using the log Pearson Type III distribution. The skew map is commonly used despite the fact that it's inaccurate, lacks a conceptual basis, and does not reflect watershed processes. Attempts at regionalizing station skew using regression analysis have only provided marginal improvements in accuracy, possibly because the predictor variables are not good indicators of the physical characteristics that influence the variation in skewness. Therefore, a new approach is needed to improve skew estimates. This research explored the potential of using a distributed model that includes predictor variables that better represent watershed storage. The results showed that watershed storage is the main factor that affects flood skew, and that increases in watershed storage causes flood skews to be algebraically more negative.Item The Effects of Building Information Modeling on Construction Site Productivity(2010) Chelson, Douglas E.; Skibniewski, Miroslaw J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Construction experiences low productivity compared to other industries, largely attributed to poor planning and communication. Building Information Modeling (BIM) is a process that is used to resolve these problems by simulating physical space and expressing design intent graphically, providing a clearer image of design conflicts or constructability issues so that they are resolved before construction begins. Productivity rates increase as BIM practices are implemented because rework and idle time are reduced for laborers. Case studies of projects utilizing BIM indicate field productivity gains from 5 to 40%, depending on how the process is managed. Although the amount of savings is guarded closely by those who measure and track the changes in their productivity rates and unknown to many contractors, there are indicators that reveal increased productivity. Key indicators of increased productivity are RFI reduction, amount of rework, schedule compliance, and change orders due to plan conflicts. Each of these affect the various stakeholders of a project to different degrees but the overall effect is a net savings for the owner ranging from a few percent for competitive bid projects to over 10% for integrated projects. BIM-enabled projects have 10% of the RFI that a typical project would have so that contractors realize an average savings of 9% in management time. Reduction of rework and idle time due to site conflicts savings for trade contractors are on the order of 9% of project costs. The abilities to prefabricate and automate site processes are also significant advantages of BIM usage experienced by trade contractors. The most significant savings are attributed to the clash detection process which eliminates conflicts in the field. These findings show that the strongest determinants of success on BIM projects in terms of site productivity are human factors rather than technical.Item OPTIMIZATION MODELS AND METHODOLOGIES TO SUPPORT EMERGENCY PREPAREDNESS AND POST-DISASTER RESPONSE(2010) Chen, Lichun; Miller-Hooks, Elise; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses three important optimization problems arising during the phases of pre-disaster emergency preparedness and post-disaster response in time-dependent, stochastic and dynamic environments. The first problem studied is the building evacuation problem with shared information (BEPSI), which seeks a set of evacuation routes and the assignment of evacuees to these routes with the minimum total evacuation time. The BEPSI incorporates the constraints of shared information in providing on-line instructions to evacuees and ensures that evacuees departing from an intermediate or source location at a mutual point in time receive common instructions. A mixed-integer linear program is formulated for the BEPSI and an exact technique based on Benders decomposition is proposed for its solution. Numerical experiments conducted on a mid-sized real-world example demonstrate the effectiveness of the proposed algorithm. The second problem addressed is the network resilience problem (NRP), involving an indicator of network resilience proposed to quantify the ability of a network to recover from randomly arising disruptions resulting from a disaster event. A stochastic, mixed integer program is proposed for quantifying network resilience and identifying the optimal post-event course of action to take. A solution technique based on concepts of Benders decomposition, column generation and Monte Carlo simulation is proposed. Experiments were conducted to illustrate the resilience concept and procedure for its measurement, and to assess the role of network topology in its magnitude. The last problem addressed is the urban search and rescue team deployment problem (USAR-TDP). The USAR-TDP seeks an optimal deployment of USAR teams to disaster sites, including the order of site visits, with the ultimate goal of maximizing the expected number of saved lives over the search and rescue period. A multistage stochastic program is proposed to capture problem uncertainty and dynamics. The solution technique involves the solution of a sequence of interrelated two-stage stochastic programs with recourse. A column generation-based technique is proposed for the solution of each problem instance arising as the start of each decision epoch over a time horizon. Numerical experiments conducted on an example of the 2010 Haiti earthquake are presented to illustrate the effectiveness of the proposed approach.Item Optimization of highway work zone decisions considering Short-term and Long-term Impacts(2010) Yang, Ning; Schonfeld, Paul M; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the increase of the number, duration, and scope of maintenance projects on the national highway system, transportation agencies face great challenges in developing effective comprehensive work zone management plans which minimize the negative impacts on road users and workers. The types of maintenance operation, timing, duration, configuration, and user impact mitigation strategies are major considerations in developing work zone management plans. Some of those decisions may not only affect road users during the maintenance phase but also have significant impacts on pavement serviceability in future years. This dissertation proposes a systematic methodology for jointly optimizing critical work zone decisions, based on analytical and simulation models developed to estimate short-term impacts during the maintenance periods and long-term impacts over the pavement life cycle. The dissertation starts by modeling the effects of different work zone decisions on agency and user costs during the maintenance phase. An analytic one-time work zone cost model is then formulated based on simulation analysis results. Next, a short-term work zone decision optimization model is developed to find the best combination of lane closure and traffic control strategies which can minimize the one-time work zone cost. Considering the complex and combinatorial nature of this optimization problem, a heuristic optimization algorithm, named two-stage modified population-based simulated annealing (2PBSA), is designed to search for a near-optimal solution. For those maintenance projects that may need more detailed estimation of user delay or other impacts, a simulation-based optimization method is proposed in this study. Through a hybrid approach combining simulation and analytic methods along with parallel computing techniques, the proposed method can yield satisfactory solutions while reducing computational efforts to a more acceptable level. The last part of this study establishes a framework for jointly optimizing short-term and long-term work zone decisions with the objective of maximizing cost-effectiveness. Case studies are conducted to test the performance of the proposed methods and develop guidelines for development of work zone management plans.Item TOWARD DEVELOPMENT OF STANDARDS FOR WEB-BASED PROJECT MANAGEMENT SYSTEM(2010) Sangworawong, Supasit; Skibniewski, Mirosław J.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Web-based Project Management Systems (WPMS) are based on extranet applications for project management. Currently, WPMS software vendors are offering WPMS products on the e-business market. Because of lacking WPMS standards, users lack uniform tools to decide whether the available systems have relevant capabilities to meet their requirements. This research defines an initial approach to the creation of a WPMS standard. Such a standard can provide WPMS users with a rationale for WPMS selection mechanism. The research proposes an outline of an approach to future WPMS standard design.Item Using Radio-Frequency Identification Technology To Measure Asphalt Cooling(2010) Pfeiffer, Grant Howard; Schwartz, Charles W; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Realistic prediction of asphalt temperatures as a function of time during paving is essential for optimizing compaction operations. Continued compaction after the asphalt lift has dropped below a critical threshold temperature may result in particle breakage and degradation of the material properties. To address this issue, this study evaluates the feasibility of using Surface Acoustic Wave (SAW) based Radio-Frequency Identification (RFID) technology to measure HMA temperatures via wireless sensors during paving. The survivability and temperature measurement capabilities of the SAW RFID sensors are demonstrated in the field. The measured asphalt cooling curves (temperature versus time) are compared with predictions from previously developed theoretical models for mat cooling. The prediction accuracy of these models is improved via a field calibration procedure using measured temperatures from the SAW RFID sensors. The predictions from the calibrated theoretical model are reasonable and agree well with the measured temperatures in the field.Item Analysis and behavior investigations of box girder bridges(2010) Begum, Zakia; Fu, Chung C; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Due to efficient dissemination of congested traffic, economic considerations, and aesthetic desirability horizontally curved steel box girder bridges have become increasingly popular nowadays in modern highway systems, including urban interchanges. Although significant research has been underway on advanced analysis for many years to better understand the behavior of all types of box-girder bridges, however, the results of these various research works are scattered and unevaluated. Hence, a clear understanding of more recent work on straight and curved box-girder bridges is highly desired. The non-composite steel section must support both the fresh concrete and the entire construction loads hence steel box girders are at their critical stage during construction. In the current study, non composite straight and curved steel boxes are analyzed with beam and shell elements using the three dimensional finite element analysis and their behavior is investigated. The present research addresses comparison using beam and shell element models of the straight and curved box girder bridge. This task involves examining the stress patterns obtained using static three-dimensional finite element modeling. Comparisons are made between stresses obtained for the straight and curved box girder bridges, from the beam element model and shell element model for each. Further, the finite element results are compared to the BEST center program DESCUS-II results. Finally, the parametric investigations are performed on the curved steel box model to evaluate the effects of several important parameters on the behavior of the girder.Item Transaction Cost Estimation Model for US Infrastructure Public Private Partnerships.(2010) Farajian, Mortezs; Cui, Qingbin; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Due to special characteristics of Public Private Partnerships (PPPs), the ―transaction cost‖ in PPPs is more than other delivery methods. Although there have been some attempts to study transaction costs in PPPs in Europe, transaction costs of PPPs in the US has not been explored well, and the need to develop a standard cost breakdown structure to track, measure and estimate transaction costs in PPP projects is paramount. This thesis covers a theoretical discussion about the definition of transaction costs and different factors affecting them, and based on the mapping of PPP transaction activities to project costs, presents a cost breakdown structure (CBS) as well as a cost accounting matrix. This accounting model is justified in chapter four using two case studies: I-495 HOT lanes project in Virginia, and I-595 improvements in Florida. Finally, in chapter 5 a template for an estimating model which can be used in procurement transaction cost estimates is developed based on the data collected from some infrastructure PPP projects in Europe, and applying Bayesian theory.Item UNDERSTANDING THE IMPACT OF INCIDENTS AND INCIDENT MANAGEMENT PROGRAMS ON FREEWAY MOBILITY AND SAFETY(2010) Chou, Chihsheng; Miller-Hooks, Elise; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Despite significant technological achievements over past decades, and institutional support for Intelligent Transportation System (ITS), it is not possible to prevent all traffic incidents. Numerous incidents occur every day along U.S. freeways and traffic incident management (TIM) programs have been proposed and implemented to mitigate their impact. This dissertation proposes various tools to aid in the evaluation of proposed TIM programs, contributing, thus, to the general study area of freeway incident management. In addition, moving violations specific to concurrent flow lane operations are conceived as a type of transient incident. Their impact on mobility and safety is considered. Techniques to address four key areas are proposed. First, a methodology that considers the dynamics of incident impact given a primary incident's properties and prevailing traffic conditions for identifying secondary incidents from a database is proposed. This method is computationally efficient and overcomes deficiencies of other existing techniques, with utility in any context in which the study of secondary incidents is warranted. A three-stage time-saving process is developed for conducting TIM program benefit evaluations. The process aids in sampling a relatively small set of good quality incident scenarios that can represent historical incident data and overcomes the computational burden encountered when evaluating TIM program's benefit by simulation. Modeling techniques are proposed for simulating violations associated with the operation of concurrent flow lanes. Results from a case study show significant impact to mobility that grows nonlinearly with increasing violation rate. Such illegal traffic maneuvers contribute to increased speed variation and congestion, ultimately affecting safety. Finally, diversion strategies that exploit existing capacity of managed lanes for the purpose of reducing the impact of an incident in the general purpose lanes are evaluated. Simulation modeling methodologies were developed for modeling freeway incidents and studied diversion strategy implementations. Experimental findings indicate benefits of diversion that are contrary to qualitatively developed recommendations in the literature.