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Title: DYNAMIC ANALYSIS OF UNCERTAIN STRUCTURES USING IMPRECISE PROBABILIY
Creator: Bergerson, Joshua D.
Date: 2014, 2014-05
Description: A new method for dynamic response spectrum analysis of structures with uncertainty in their mechanical properties utilizing the notion of...
Show moreA new method for dynamic response spectrum analysis of structures with uncertainty in their mechanical properties utilizing the notion of imprecise probability is developed. This finite-element-based method is capable of obtaining probabilistic bounds of the dynamic response of the structure with uncertainty defined by enveloping p-boxes. The developed method obtains probabilistic bounds on 1) the mode shapes, 2) modal coordinates, and 3) modal participation factor, leading to the p-boxes of modal responses. Finally maximum modal responses are combined to obtain the structure’s maximum total response with consideration of uncertainty. Numerical examples demonstrating the developed method are included. Keywords: Structural Dynamics, Uncertainty, Imprecise Probability, P-Box.
PH.D in Civil Engineering, May 2014
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Title: MATERIAL INVENTORY CONTROL AND MANAGEMENT SYSTEM IN CONSTRUCTION USING GIS APPLICATIONS AND A "HYBRID" TRACKING SYSTEM
Creator: Le, Kiet Tuan
Date: 2017, 2017-05
Description: Material inventory control and management is simply the process by which an organization is supplied with the goods and services that it needs...
Show moreMaterial inventory control and management is simply the process by which an organization is supplied with the goods and services that it needs to achieve its objectives of buying, storing and moving materials. There are usually plenty of materials in a construction site. A large amount of stored materials can meet unexpected demands, and can prevent future purchases that can be affected by an escalation of material prices. However, a large amount of stored materials can also cause negative impacts such as increased costs for storing redundant inventory, and decreased construction productivity. Therefore, a proper material inventory control and management system is critical for economy and efficiency in construction projects. A material inventory control and management system consists of two main elements: inventory control and inventory management. Inventory control is the process of monitoring the flow of materials on the construction site beginning when materials are received from manufacturers and ending when those materials are used in production. Inventory management is the practice overseeing and managing the ordering, storage and use of materials on the construction site. In this study, an automated material inventory control and management system is developed using Geographical Information System (GIS) applications and a “hybrid” tracking system to identify the need for materials, order, track, transport, store, control the inventory, circulate on site, and incorporate into production. The proposed system allows users to have access to real-time information about the materials on the construction such as: the arrival of materials, the amount of materials received, the status of materials (either in storage area or in-production), and the up-to-date information about site stocks. Furthermore, the system provides users the ability to make correct and timely decisions regarding materials on the construction site.
Ph.D. in Civil Engineering, May 2017
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Title: METHODOLOGY FOR VEHICLE EMISSION IMPACTS ANALYSIS FROM SIGNAL TIMING OPTIMIZATION OF AN URBAN STREET NETWORK
Creator: Lu, Pu
Date: 2017, 2017-05
Description: The pace of urban street capacity expansion is much slower than the growth of vehicle travel, leading to several traffic congestions. To...
Show moreThe pace of urban street capacity expansion is much slower than the growth of vehicle travel, leading to several traffic congestions. To mitigate traffic congestion expanding capacity is not feasible for many cases due to the high cost and space restriction. Improving the efficient use of the available capacity becomes the solution. Traffic signal optimization is one of the most widely used ways of efficient capacity utilization. Concurrent to traffic signal optimization, more smooth traffic operations in term of reasonably higher speed and a reduced traffic delay will in turn change vehicle emissions. This research aims to quantify changes in vehicle emissions resulted from traffic signal optimization by introducing a new methodology for quantifying network wide vehicle emissions and real world application in of the Chicago urban network for validation. The proposed methodology considers undersaturation and oversaturation of traffic conditions and urban street segments with varying speeds for different types of vehicles and pollutants by hour of the day and location within the network. It begins with information collection and research through a review of existing methods for urban street network vehicle emission estimation, intersection vehicle emission evaluation, and the running vehicle emission modeling. The proposed methodology focuses on three elements: estimation of emissions from vehicles stopped at intersections and for vehicles cruising along segments, as well as analysis of network wide vehicle emissions and changes in overall network vehicle emissions by time of the day and by areas. Major steps of methodology application included the use of Chicago TRANSIMS model implementing optimized signal timing plans to obtain refined traffic volumes at intersections and on segments, increased vehicle operating speeds, changed green splits, and vehicle compositions for all intersections and segments in the urban street network, the application of an intersection vehicle emission model for stopped vehicles and a segment vehicle emission model for vehicles cruising on segments, and the network wide analysis of vehicle emission changes by vehicle type and pollutant type in a 24-hour period within an urban street network, respectively. The proposed methodology for intersection vehicle emission estimation was successfully applied to a dense urban street network in Chicago for each approach per cycle and then extended for intersections in hours of the day to analyze the impacts of traffic changes at intersections on exhaust changes. In order to develop the network vehicle emission analysis method, it is essential to evaluate the segment vehicle emissions. This is achieved by using the concept of vehicle specific power which is used to estimate emissions of cruising vehicles considered along with vehicle speeds and speed changes and hence analyzing changes in segment vehicle emissions affected by traffic volume changes derived from signal timing optimization. The decreased number of vehicles stopped at intersections by applying signal timing optimization will reduce intersection emissions, hence reducing overall network vehicle emissions. In addition to have vehicle emissions got reduced at intersections, the increasing vehicle speed for vehicles on segments could further reduce vehicle emissions on segments.
Ph.D. in Civil Engineering, May 2017
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Title: INVESTIGATING THE SIGNIFICANCE OF HALF-SATURATION COEFFICIENTS ON WASTEWATER TREATMENT PROCESSES
Creator: Shaw, Andrew Robert
Date: 2015, 2015-05
Description: This research is focused on the half-saturation coefficient (KS), which is an important, but often overlooked, parameter in the Monod equation...
Show moreThis research is focused on the half-saturation coefficient (KS), which is an important, but often overlooked, parameter in the Monod equation commonly used to describe biological wastewater treatment processes. Following an initial literature review, the research uses data for a denitrifying activated sludge process to show that KS is a function of the maximum rate and, further, that the relationship can be described either using a simple linear regression or by modeling diffusion explicitly. Building on this initial investigation of a particular treatment system, the research introduces and uses a “porter-diffusion” model that approximates diffusion to a linear equation for KS in the Monod equation. This is used to describe the linear relationship between KS and maximum rate for four different biological wastewater treatment systems. Finally, a sensitivity analysis is carried out on the parameters in the porter-diffusion model to show that r0 – a measure of cell size or diffusion distance – is the most sensitive parameter for a simple activated sludge process model based on a modified version of the International Water Association (IWA) activated sludge model #1 (ASM1). Overall this research has shown that in all of the biological wastewater treatment systems investigated in this thesis: (1) KS is not a constant but is a function of the maximum rate; (2) diffusion is a dominant mechanism that influences KS; (3) that a suitable expression for KS can be estimated using the porter-diffusion model, a linear data fit, or by modeling diffusion explicitly; and (4) measurements of KS in the laboratory must be carried out at the same food-to-microorganism (F/M) ratio as the full-scale system under investigation.
Ph.D. in Civil Engineering, May 2015
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Title: SEISMIC STUDY OF DUCTILE AND NON-DUCTILE CONCENTRICALL1 BRACED FRAMES
Creator: Sutchiewcharn, Narathip
Date: 2013, 2013-07
Description: Braced Frames, both ductile and non-ductile systems, are in high demand due to their considerable strength and attractiveness. Therefore, the...
Show moreBraced Frames, both ductile and non-ductile systems, are in high demand due to their considerable strength and attractiveness. Therefore, the better understanding of their behaviors will be beneficial, in which, is the focus in this study. With different failure modes expected based on design methodology, the study of non-ductile system is focused on connections and their contributions toward performance of frame systems, while the ductile system is concentrated on the behavior of braces itself. For non-ductile system with the model-based simulation approach, local brace connection models were developed extending from the validation with the existing specimens. Then, the extensive seismic global performances including local joints, from both local brace and gravity frame connections, are evaluated with the adaptation of collapse methodology outlined in FEMA-P695. For ductile system, with the expectation of hinges formed in braces causing by buckling, the global performances under reversal loadings, e.g. ground motions, are in jeopardy due to the strength degradation. Taking advantage of FEM simulations in addition to testing, the proposed tube-in-tube brace configuration is introduced as buckling-controlled brace (BCB). The effects of parameters are studied using analytical models. The performances observed from proposed tube-in-tube configuration are satisfied under both monotonic and cyclic loadings.
PH.D in Civil Engineering, July 2013
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Title: HEURISTIC DECISION-MAKING MODEL FOR ELECTRICAL FOREMEN WHEN WORKFLOW IS DISRUPTED
Creator: Pandey, Arjun R.
Date: 2016, 2016-05
Description: The decision-making process used by construction foremen at a job site when the workflow is disrupted was investigated in this study. The...
Show moreThe decision-making process used by construction foremen at a job site when the workflow is disrupted was investigated in this study. The foremen’s decision-making process was mapped and then modeled to a heuristic model. This study focuses on cognitive decision or psychological heuristic models. The study shows that construction foremen use a heuristic decision model in their decision-making. The capability of heuristic to yield fast decision is very useful in construction because it is common for a construction foreman to experience several disruptions during the course of a single workday. With heuristic decision-making, a work-around decision can be rapidly and effectively made following a construction site disruption. Understanding the ability of heuristics to facilitate rapid and effective decision-making will help the construction industry to save time and increase productivity. Research was conducted in order to map a decision process that foremen were using in their decision-making and to develop a model for a heuristic decision-making process. Interviews were conducted with 22 construction foremen in the electrical trade in 88 real disruption cases in order to understand how decisions were made after disruptions occurred. Interviews were subsequently conducted with 10 additional industry foremen in 10 real disruption cases to validate the data. Using this data, a heuristic decision-making model was developed. To validate this model, a survey was conducted with another 11 industry foremen. The findings indicate that construction foremen currently use a heuristic decision-making model known as “determinant decision attribute” (referred to as DDA) heuristics model. This DDA heuristic model was compared to the similar model with equal weighing and elimination by aspects (referred to as EW/EBA) to assess the performance of the heuristic. The DDA heuristic model correctly predicted, on average, 91% of the time what foremen’s decisions were as to which decision task to choose to assign or re-assign to crew members. Whereas, the EW/EBA model correctly predicted, on average, 82% of the time, the foremen’s decisions. A computer program was also developed for DDA heuristic model to help foremen expedite the process of their decision-making.
Ph.D. in Civil Engineering, May 2016
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Title: LAND USE EFFECTS ON WATER QUALITY: BUILDING A FRAMEWORK FOR CHICAGO RIVER WATERSHED
Creator: Mahdi, Naila Ghidey Ismail
Date: 2012-05-09, 2012-05
Description: The purpose of this study is to introduce a framework that enables a holistic watershed approach that models the dynamics of water quality and...
Show moreThe purpose of this study is to introduce a framework that enables a holistic watershed approach that models the dynamics of water quality and landuse in a highly urbanized watershed. The landuse-water quality relationship is a complex relationship and has not been adequately addressed for highly urbanized watersheds. Factors such as inadequate urban planning, increase of impervious areas and dynamics of population growth are some of the reasons for the complex relationship. Also point sources are always easy to be identified and controlled unlike nonpoint sources such as urban storm runoff. Both quantities and transport pathways of pollutant inputs are impacted by land use in the watershed. So, examining the factors that govern the relationship between different land uses and water quality within a watershed can give insights and important information about existing and potential sources of contamination. The two backbone concepts in this study are the holistic watershed perspective and the role of historical data records as part of assessment, modeling and integration tools of the watershed framework. Analysis of the records will explain watershed conditions identifying the major problem areas and justify the modeling and post analysis procedures. Data sources are often important but data availability, heterogeneity and conformity are the main challenges in integrating these sources. This research presents an approach to integrate the watershed data in a single repository and methodologies for analyzing and assessing the watershed using data warehouse and data mining technologies. A multi-dimensional model that supports complex querying of watershed data and discovery of trends and patterns in data by incorporating 40 years worth of watershed data from different source agencies in a central repository is introduced. Also, the discipline of data driven modeling was introduced in this thesis using the developed central repository. Several regression and classification algorithms were presented and assessed for their appropriateness for predicting total nitrates using few watershed attributes. The results show acceptable prediction accuracy. Five years of water quality simulation using the multi-purpose environmental analysis system BASINS coupled with the comprehensive, conceptual, and continuous simulation watershed scale model HSPF resulted in export coefficients for level (III), detailed land use for the Chicago River watershed. The water quality simulation approach utilized in this research to generate the coefficients constitutes a new contribution to the Chicago River watershed and other highly urbanized watersheds. The continuous calibrated and validated model can be used in the investigation and analysis of different scenarios and possible future conditions, thus providing a planning tool for regulatory environmental agencies. The data driven models developed can be used as operation tool to maintain the water quality parameters especially if TMDL and WQS are developed for Chicago River Watershed. So the framework proposed for this study can be considered robust with the proposed integration, planning and operating techniques and tools. Furthermore, an optimization tool is introduced in the future work section.
Ph.D. in Environmental Engineering, May 2012
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Title: METHODOLOGY FOR PERFORMANCE BASED TRANSPORTATION SYSTEMS MANAGEMENT SIMULTANEOUSLY CONSIDERING DEMAND AND SUPPLY, WITH PRICING CONSIDERAnON
Creator: Patel, Harshingar
Date: 2015, 2015-05
Description: The ever growing demands for the use of transportation infrastructure and its maintenance and repairs at an acceptable level of service are...
Show moreThe ever growing demands for the use of transportation infrastructure and its maintenance and repairs at an acceptable level of service are the prime concern for transportation agencies today. The available financial resources can never be sufficient to match the exorbitantly high requirements for construction, maintenance and rehabilitation of transportation systems. With the advent of the technological revolution, the intelligence transfer amongst various engineering fields has made it possible to reduce transportation costs. However, the slow growing budget caused by economic recession and revenue decrease over time puts transportation agencies under enormous pressure to effectively restore the deteriorated transportation facility and system operation conditions under the budget constraint. The proposed research aims to utilize the concept of roadway pricing coupled with a holistic framework of asset management to support performance-based management of transportation systems and help transportation agencies achieve the future vision of the nation's strategic planning requirements to enable sustainable management of the system. A computational study for the City of Chicago’s central district is conducted by using the proposed roadway pricing framework. The proposed roadway pricing framework can be utilized for urban as well as rural regions, by public as well as private agencies, to manage the system in a sustainable manner, by means of fair pricing to the users of the system, for their facility condition and usage impacts.
Ph.D. in Civil Engineering, May 2015
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Title: INVESTIGATING THE MEDIATION OF HEMOGLOBIN PROTEINS IN NITRIFICATION AT LOW DISSOLVED OXYGEN CONDITIONS
Creator: Arnaldos, Marina Orts
Date: 2012-10-30, 2012-12
Description: Due to the high aeration and energy requirements of nitrifying activated sludge processes, there is great interest in developing biological...
Show moreDue to the high aeration and energy requirements of nitrifying activated sludge processes, there is great interest in developing biological nitrifying processes that operate efficiently under low dissolved oxygen (DO) conditions. In this framework, the present study has investigated the acclimation of ammonia-oxidizing communities (AOC) to low DO concentrations. Under controlled laboratory conditions, two sequencing batch reactors seeded with activated sludge from the same source were operated at high DO (near saturation) and low DO (0.1 mg O2/L) concentrations for a period of 385 days. Stable and complete nitrification at low DO after an acclimation period of approximately 140 days was demonstrated. Modeling of oxygen transfer and uptake behavior demonstrated the low DO reactor to achieve equal performance to the high DO reactor, when the latter is operated at design DO concentration (2 mg O2/L), with approximately 20 % improvement in aeration requirements and oxygen mass transfer efficiency. The effect of DO on AOC dynamics was evaluated using the 16S rRNA gene as the basis for phylogenetic comparisons and organism quantification. Ammonium consumption by ammonia-oxidizing archaea and anaerobic ammonia-oxidizing bacteria was ruled out in both reactors. Even though N. europaea was the dominant AOB lineage in both SBRs at the end of operation, this enrichment could not be linked to acclimation to oxygen-limited conditions. This finding challenges the hypothesis that low DO conditions select for ammonia-oxidizing lineages characterized by high oxygen affinities, and points to the alternative mechanism of a physiological change of a generalist nitrifying community. Acclimation brought about increased specific oxygen uptake rates and enhanced expression of a particular heme protein in the soluble fraction of the biomass in the low DO reactor as compared to the high DO reactor. The heme protein induced was determined not to be any of the enzymes playing a role in ammonia metabolism of ammonia oxidizing bacteria, including a soluble oxidase and soluble peroxidase of unknown function. Further molecular studies are required to verify the hypothesis put forward in this study that the heme protein detected is a hemoglobin.
PH.D in Environmental Engineering, December 2012
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Title: WIND TURBINE FARMS IMPACT ON POLLEN TRANSPORT DISPERSION PATTER S
Creator: Hsu, Chin Yu
Date: 2012-11-28, 2012-12
Description: Wind energy has become more and more popular because electricity generation by wind power brings much less environmental impacts than...
Show moreWind energy has become more and more popular because electricity generation by wind power brings much less environmental impacts than conventional energy generation using coal. Also, energy generated by wind power does not require expensive fuel imported from overseas. Since the land in between turbines is still cultivated for crops and grazing, it is important to know the potential interference of wind turbines with pollen transport and dispersion, or the possible change of patterns established for thousands of years. However, these issues have not been studied in the literature. The co-existence of conventional crops with genetically modified (GM) crops has become a subject of debate. In particular, pollen transfer from GM crops to non-GM crops might result in the introgression of transgenes into natural populations as maize is mainly wind-pollinated. This study thus reports and assesses a comprehensive method that estimates maize pollen transport in the presence of turbines to ascertain the potential for maize pollen transport. The study on the concentrations of maize pollen transport affected by the wind turbines considers different dispersion parameters given the additional mechanical turbulence introduced by the presence of operating wind turbines. For instance, the wind turbines can increase surface roughness which subsequently causes increased mechanical turbulence. A high mechanical turbulence subsequently reduces downwind concentrations because of the mixing higher and wider into the atmosphere, which dilutes the maize pollen plume with more clean air. This study compares maize hourly concentrations and ground level flux levels inside and outside a virtual maize flux in the presence and absence of operating wind turbines. Results from a 14-day simulation of maize transport xii with and without operating wind turbines indicate that each difference of corresponding concentration and flux levels is statistically significant. Likewise, patterns of maize pollen transport inside the farm with turbine effects are significantly different from those without turbine effects. Overall, the average maize pollen concentration inside the farm in the absence of turbine effects is about 5 times greater than the corresponding maize pollen concentration with turbine effects. The total mass of maize pollen released into the air is the same whether the wind turbines are present or not. The portion of maize pollen staying inside the farm, on the other hand, is influenced by turbulence. For instance, the increased surface roughness caused by the turbine effects will increase the mechanical turbulence. Because the high mechanical turbulence carries a large portion of maize pollen away from the farm, only a small portion of maize pollen stays inside the farm due to the high turbulence that lifts maize pollen into higher levels of flow where the wind speed is stronger. In contrast, without turbine effects, a small portion of maize pollen leaves the farm while most of it deposits on the ground much sooner than it would with turbine effects. Therefore, maize pollen concentration and ground level flux in the presence of turbine effects will be greater than they are without turbine effects at a relatively far distance from the farm.
PH.D in Environmental Engineering, December 2012
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Title: DEVELOPMENT OF PERMEABLE REACTIVE FILTER SYSTEMS (PRFS) FOR TREATMENT OF URBAN STORMWATER RUNOFF
Creator: Prabhukumar, Giridhar
Date: 2013, 2013-05
Description: Urban stormwater runoff is a major contributor of pollutants to nearshore beach water of Lake Michigan and other water bodies. Reduction of...
Show moreUrban stormwater runoff is a major contributor of pollutants to nearshore beach water of Lake Michigan and other water bodies. Reduction of pollutants levels to within safe limits in urban runoff from near shore areas by means of filtration using low-impact reactive multi-media systems is the subject of research in this dissertation. The key research issues addressed are the identification of effective filter materials and laboratory-scale testing of the selected materials for permeable reactive filter systems (PRFS) that are feasible for installation in urban environment. The focus was to evaluate different media materials for removal of total suspended solids (TSS), nutrients (nitrate and phosphate), heavy metals (Cd, Cr, Cu, Pb, Ni and Zn), polycyclic aromatic hydrocarbons (naphthalene and phenanthrene) and microbial (E. coli.) contaminants from stormwater runoff to levels below standard discharge criteria. Eight different media materials were initially selected, including calcite, anthracite coal, zeolite, sand, iron-oxide coated sand (IOCS), iron filings, perlite and biochar. Of these, calcite (C), zeolite (Z), sand (S) and iron filings (Fe0) were screened based on preliminary column experiment results and used for further studies. Physical and chemical characterization studies were carried out to understand the material properties. Contaminant attenuation studies with lab-scale column experiments for the four individual media materials (C, Z, S and Fe0) were conducted with synthetic stormwater solution containing all the aforementioned pollutants. Results showed that calcite and sand were efficient in TSS, nutrients and polycyclic aromatic hydrocarbons (PAHs) removal, zeolite was efficient for metals removal and the only material that was able to lower E. coli level to below its safe xv limit of 126 most probable number (MPN) per 100ml, and iron filings was efficient in nutrients and metals removal. Column experiments were also conducted with three mixed media compositions, C-Z-S, C-Z-Fe0 and C-Z-S-Fe0. The results indicated that a multi-media based filtration system can perform efficiently to treat a wide range of pollutants and runoff flow conditions. Finally, several conceptual designs for PRFS were proposed that are suitable for application at various urban locations.
PH.D in Environmental Engineering, May 2013
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Title: FATIGUE AND BARKHAUSEN EFFECT
Creator: Tong, Wei
Date: 2013, 2013-05
Description: Piezomagnetism designates a change in the magnetization of materials induced by mechanical actions such as tension or compression. The type of...
Show morePiezomagnetism designates a change in the magnetization of materials induced by mechanical actions such as tension or compression. The type of Barkhausen effect that occurs in this work consists of sudden, discontinuous jumps in a material’s magnetization that appear in response to smooth (continuous) stress variations. A series of strain controlled fatigue tests with an alternating sinusoidal waveform were carried out to study the relationship between the endurance limit and the Barkhausen effect. Results of fatigue tests on steel specimens exhibiting Barkhausen pulses at various stages are reported and a threshold-crossing analysis is applied to the test results. These studies show that when the fatigue limit is approached, the Barkhausen pulses become, in general, more intense in amplitude and quantity than at other stress levels. A hypothetical mechanism is proposed that relates the intensity of the Barkhausen response to the inception of micro-cracking and rearrangements of the mechanical lattice at the microscopic level.
PH.D in Civil Engineering, May 2013
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Title: SEISMIC STUDY OF HYBRID SHEAR WALL SYSTEM
Creator: Xu, Lifeng
Date: 2013, 2013-07
Description: This thesis represents the seismic behavior of new hybrid shear wall system, which consists of two exterior precast wall layers and one...
Show moreThis thesis represents the seismic behavior of new hybrid shear wall system, which consists of two exterior precast wall layers and one interior cast-in-place concrete layer. The “sandwich” shaped shear walls were already tested as a full scale specimen subjecting to vertical pressure and cyclic horizontal load in Anhui University of Architecture, China (2010). A series of 3D non-linear finite element models which include all significant details and specifications were then created in ABAQUS to simulate the experiments. The pushover analyses method was employed to reproduce the test procedures. The response of the structure was computed both at macro and micro level at the result in order to validate the correctness of the analytical model. After verifying the good agreement between the experimental observations and simulation results, an extended parametric study was conducted towards this hybrid shear wall system to explore its damage mechanism and design optimization. Based on hybrid shear wall's specific seismic resisting capacity which derived from the previous simulation, a series of 2D models were created in SAP2000 to evaluate the seismic performance of hybrid shear wall structure. What's more, in order to precisely represent the 3D model effect into 2D model in SAP2000,3D model was created in ABAQUS to account for the influence of semi-rigid connection between the concrete diaphragm and hybrid shear wall. After applying the ability of semi-rigid connection and hybrid shear wall, pushover method and time history analysis were conducted towards this 18 story structure model. The global seismic performance factor is finally evaluated according to the FEMA-P695.
PH.D in Civil Engineering, July 2013
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Title: MANAGING THE BIDDING PROCESS FOR THE CONSTRUCTION OWNER – DETECTION AND PREVENTION OF UNBALANCED BIDS AND COLLUSIVE BIDS
Creator: Chotibhongs, Ranon
Date: 2011-09, 2011-12
Description: There are two major problems that affect bidding efficiency: unbalanced bidding and collusive bidding. Unbalanced bidding is a serious...
Show moreThere are two major problems that affect bidding efficiency: unbalanced bidding and collusive bidding. Unbalanced bidding is a serious unethical problem in the construction industry. The owner may end up paying more money if the bid is unbalanced by the contractor. A bid can be rejected by the owner if it is unbalanced. A bidder unbalances a bid by inflating the unit price of some line items and reducing the unit price of other line items. Frontloading is the most common practice where a bidder can mathematically unbalance a bid by overstating the unit price of line items scheduled to be performed early in the project and understating the unit price of line items performed later. A bidder can also overstate the unit price of a line item whose quantity was somehow underrated by the engineer. If the owner proves that a mathematically unbalanced bid costs more to perform, the bid is said to be materially unbalanced, in which case the owner can reject the bid. A model is presented that formalizes and automates the process of detecting mathematically and materially unbalanced bids by comparing line item prices with the engineer’s estimates or the average prices offered by the bidders. This model allows owners to detect and reject unbalanced bids, and deters bidders from unbalancing their bid. Another matter that inflates bids and reduces bidding efficiency is collusion. Collusion is an insidious issue in the construction industry. Even though, it is widely acknowledged as unethical and illegal, there are not many research studies conducted to detect collusive bidding. This study proposes a two-step method to detect collusive bidding by analyzing historical bidding data provided by a construction owner. The construction owner in this study was a public agency that commissioned 108 construction projects that was worth $1.3 billion during a 10-year study period (2001-2010). The first step involves indentifying the potential cartel bidders using the residual test and the cost structure stability test developed in earlier work. The second involves comparing the behavior of the potential cartel bidders and non-cartel bidders by analyzing bid distributions, their cost dispersion, and the differences in their cost structures. After conducting the tests, it was found that the suspected cartel bidders identified in Step 1 behaved in ways to confirm collusion. Also, in an unrelated search, it was found that two of the six potential cartel bidders who were identified in this study had been audited by the public agency for bid fraud, and that another potential cartel bidder had been found guilty by the courts and forbidden from doing business with the public agency.
Ph.D. in Civil Engineering, December 2011
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Title: METHODOLOGY FOR URBAN AREA SNOW REMOVAL USING NEW MACHINE AND PERFORMANCE-BASED ANALYSIS
Creator: Neishapouri, Mohammad
Date: 2015, 2015-12
Description: The need for alternative methods that facilitate removal of snow on urban streets with minimal pavement and bridge damages, vehicles...
Show moreThe need for alternative methods that facilitate removal of snow on urban streets with minimal pavement and bridge damages, vehicles corrosions, and environmental impacts due to use of chemicals and salts has been growing over time. Conversely, this issue has not been thoroughly investigated. This is particularly true for large urban areas where the snow removal machine and background traffic share already congested streets. In this research, a new methodology is introduced for effectively managing snow removal that involves new machine and performance-based analysis. The new machine aims to melt snow and ice using technically adequate mechanical system including special engine, heat pumps and very fast ventilation pumps in order to suck and discharge water from pavement surface to road sides. The performance-based analysis employs a life cycle cost analysis approach to estimate reductions in expenditures to pavements and bridges, and vehicle corrosions of background traffic as a result of using new machine for snow melting instead of using chemicals and salts; and an optimization model for effective dispatching of new machine across a large area, leading to a significant level of travel timing savings to the background traffic owning to shorter duration oftravel way closures. The proposed methodology is implemented in a computational study to examine the current snow removal programs in the city of Chicago for a typical winter day involving moderate and severe snowfalls that correspond to its 50 percent and 100 percent programs for filed dispatching one-half and all snow plow trucks. Compared with the use of snow removal trucks coupled with chemicals and salts, the use of new machine could result in better equivalent annualized savings as benefits component and less amount of cost components which cause the project implementation has benefit to cost ratio Xl11The need for alternative methods that facilitate removal of snow on urban streets with minimal pavement and bridge damages, vehicles corrosions, and environmental impacts due to use of chemicals and salts has been growing over time. Conversely, this issue has not been thoroughly investigated. This is particularly true for large urban areas where the snow removal machine and background traffic share already congested streets. In this research, a new methodology is introduced for effectively managing snow removal that involves new machine and performance-based analysis. The new machine aims to melt snow and ice using technically adequate mechanical system including special engine, heat pumps and very fast ventilation pumps in order to suck and discharge water from pavement surface to road sides. The performance-based analysis employs a life cycle cost analysis approach to estimate reductions in expenditures to pavements and bridges, and vehicle corrosions of background traffic as a result of using new machine for snow melting instead of using chemicals and salts; and an optimization model for effective dispatching of new machine across a large area, leading to a significant level of travel timing savings to the background traffic owning to shorter duration oftravel way closures. The proposed methodology is implemented in a computational study to examine the current snow removal programs in the city of Chicago for a typical winter day involving moderate and severe snowfalls that correspond to its 50 percent and 100 percent programs for filed dispatching one-half and all snow plow trucks. Compared with the use of snow removal trucks coupled with chemicals and salts, the use of new machine could result in better equivalent annualized savings as benefits component and less amount of cost components which cause the project implementation has benefit to cost ratio respectively 2.15 and 2 by CPI analysis and 3 and 3.04 by CCI analysis. Compared with the current practice of filed dispatching of snow plow trucks or new machine for snow removal, the optimization model for vehicle dispatching could further improve the snow removal productivity by 2-4 percent for the 100 percent program and 3-8 percent for the 50 percent program, respectively.
Ph.D. in Civil Engineering, December 2015
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Title: A BAYESIAN UPDATING APPROACH IN STRUCTURAL HEALTH MONITORING FOR DAMAGE DETECTION AND ASSESSMENT
Creator: Dirbaz, Mojtaba
Date: 2013, 2013-05
Description: The primary goal of Bridge Condition Assessment (BCA) is to determine the condition of a bridge to prevent any catastrophic failure as well as...
Show moreThe primary goal of Bridge Condition Assessment (BCA) is to determine the condition of a bridge to prevent any catastrophic failure as well as to enhance the structure’s safety and serviceability. The structural health and condition of in-service bridges is generally assessed through visual inspections and nondestructive testing and evaluation (NDT/NDE) methods conducted on a pre-set schedule. However, the ratings obtained from current visual inspections on a bridge are subjective, and do not include the uncertainty inherent in the results. Moreover, the condition ratings are often based on independent inspections and do not take into account the dependence of results on previous conditions of a bridge and prior condition ratings compiled for it. Furthermore, there is also a certain level of uncertainty involved in relating subjective ratings to the actual condition of the bridge. This study is aimed at conducting a research on damage detection of existing bridges utilizing available information on their structural conditions. The first part of the research focuses on a new method for assessing the condition of a bridge based on subjective ratings obtained for the bridge. This method will hereafter be referred to as Bayesian Bridge Condition Assessment (BBCA). BBCA consists of three parts: (1) identification of condition states for structural components, (2) determination of a Damage Index (DI), a parameter to describe the extent of damage to a structural component, and (3) determination of an Updated Damage Index (UDI) using Bayesian updating approach. UDI offers an enhanced measure that incorporates not only the relation between subjective rating and the structure’s health condition, but also the significance of new information as it becomes available. The basic assumptions and x general formulations of the Bayesian updating method is presented. Numerical illustrations are provided to demonstrate the applicability of the method to highway bridges. It is shown that the method described in this study is especially applicable to bridges for which visual inspection data are compiled on a periodic basis. One of the methodologies for damage detection and assessment is to use sensor data for identifying the modal characteristics of the structure. The second part of this research focuses on improving upon damage detection methods using sensor and/or modal data. Thus a new method for damage detection and assessment of structures using finite element analysis, and modal data is developed and demonstrated. This method will hereafter be referred to as Bayesian Structural Condition Assessment (BSCA). Using this method, (1) a Finite Element (FE) design model of the structure (undamaged) is constructed; (2) the measured modal data is updated using a Bayesian framework; and (3) the FE model of existing structure (with possibility of damage) is obtained using updated modal data based on an iterative optimization method that is used in estimating the stiffness of the damaged structure. Using these steps, the location and extent of any possible damage is then determined based on the difference between a structural element stiffness for the “as built condition” and “damaged condition.” Several numerical illustrations are presented to demonstrate the capability of the method to detect the location and extent of the damage. This method has been applied to a structural health monitoring benchmark problem; and it has been shown that it can identify the location and extent of damage with more accuracy than most other existing models. Keywords: Bayesian Updating, Condition Assessment of Structures, Modal Data, Visual Inspections, Finite Element Model, Bridges
PH.D in Structural Engineering, May 2013
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Title: NEW DIRECTIONS IN POST-EARTHQUAKE FIRE HAZARD ANALYSIS WITH APPLICATIONS TO MIDWESTERN UNITED STATES
Creator: Farshadmanesh, Pegah
Date: 2017, 2017-05
Description: Post-earthquake fire ignition (PEFI) can lead to severe structural damage following an earthquake. Estimating the risk of such ignitions in...
Show morePost-earthquake fire ignition (PEFI) can lead to severe structural damage following an earthquake. Estimating the risk of such ignitions in buildings and identifying methods to abate it are essential steps in an overall effort to mitigate the impact of post-earthquake fires in urban areas. While several models have been developed for areas with available historical PEFI data, such as the Western United States, no such models have been developed for areas with little or no data specific for post-earthquake fires. Examples of such areas are seismic regions in the Midwestern United States. The lack of PEFI data for these areas is due to the fact that at the time of several significant earthquakes in the early nineteenth century, most earthquake-stricken communities where rural. With the growth of urban areas in the region, a need exists for a methodology that can be effectively used in estimating PEFI risks when no or little historical data is available. In this research, it was found that models for PEFI risk estimation may indeed be developed using available data on ignitions for normal conditions as a basis and then using some type of a modification factor to account for the significance of future earthquakes. This modification factor depends on the characteristics of the region in terms of seismic activities and the type and distribution of buildings and their potential in promoting ignitions. The term “normal condition ignition” (NCI) refers to an ignition that occurs due to everyday activities and routine operations in a building. In a residential building, such activities include, for example, operating heating units and burners, cooking, and mechanical malfunction of appliances. In this research, it was found that four factors specifically affect PEFI risk and can be used to develop models for risk estimation. These are (1) spatial characteristics such as geographic concentration of particular building types; (2) ignitability characteristics, such as the sources of ignitions in a particular building type, (3) earthquake characteristics (such as the peak ground acceleration); and (4) temporal characteristics, such as the time of the earthquake and seasonality. Accordingly, models for estimating the risk of post-earthquake fire ignition occurrence are developed. These models are tested, and the model parameters calibrated, using information in areas for which both the NCI and PEFI data are available (such as in the Western United States). To illustrate the applicability of the models developed and proposed in this study, St. Louis City is considered. This constitutes a major urban area vulnerable to potential future seismic activities because of proximity to the New Madrid Fault Zone. Using the NCI data for this area, PEFI risk values are estimated based on probable future seismic activities in the region. The results are presented in terms of estimated annual risk of post-earthquake fires for the area specifically for residential buildings (such as single or multifamily dwellings). The study further discusses the significance of PEFI models, their limitations and also provides suggestions for the future continuation of the research.
Ph.D. in Civil Engineering, May 2017
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Title: MECHANISMS OF FOAMING, EFFECTS, PREVENTION, AND CONTROL IN ANAEROBIC DIGESTION
Creator: Subramanian, Bhargavi
Date: 2015, 2015-05
Description: Anaerobic digestion (AD) is an essential step to generate energy in the form of biogas from waste. Foaming during AD (AD foaming) is...
Show moreAnaerobic digestion (AD) is an essential step to generate energy in the form of biogas from waste. Foaming during AD (AD foaming) is widespread phenomenon and leads to deterioration of the AD process and operation. In extreme conditions, AD foaming poses a significant safety risk and considerable economic impacts. It is, therefore, necessary to understand the fundamentals of AD foaming to develop effective strategies that can help minimize and prevent the foaming impacts. Several aspects of AD foaming have attracted considerable research attention, however, the focus has been mainly on site specific causes and prevention. The work leading to this thesis was aimed to provide a better understanding of the AD foaming problem, to identify the underlying mechanisms, causes and contributors of foaming and to come up with foam management strategies for full-scale plants. Full-scale cylindrical digester investigations did not identify non-biological factors such as organic loading rate (OLR), mixing, and primary to waste activated sludge (PS:WAS) solids ratio as primary causes of foaming, but foam-causing filaments such as G. amarae and M. parvicella were determined to be primary causes. No foaming was observed over the duration of the study, indicating absence of a primary foaming cause even though the suspected contributors to AD foaming were present. In the case of full-scale egg-shaped digesters (ESD), foaming and foam collapse events were observed over the duration of the study over both during filamentous foaming and non-foaming seasons, indicating that the primary foaming cause requires the contributors to be present. The results of this study demonstrate that ESDs foamed due to high mixing and G. amarae counts above the threshold level (log #6 intersections/mg VSS) in mixed liquor. In both types of digesters, total solids and temperature profiles showed that reducing mixing frequency did not significantly impact digester performance or the homogeneity of the digester contents. Hence, mixing intensity optimization could be an effective strategy in addition to primary cause reduction of foam causing filaments.
Ph.D. in Environmental Engineering, May 2015
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Title: A STRUCTURAL ANALYSIS FRAMEWORK FOR CONCRETE FACED ROCKFILL DAMS
Creator: Quiroz, Juan E.
Date: 2013, 2013-12
Description: Concrete Faced Rockfill Dams (CFRD’s) are commonly built around the world. As energy demands soar and construction methods evolve, the...
Show moreConcrete Faced Rockfill Dams (CFRD’s) are commonly built around the world. As energy demands soar and construction methods evolve, the interest for construction of CFRD’s with larger heights has increased tremendously. However, because of construction of higher CFRD’s, some dams have experienced considerable fractures at the concrete faces. Well known cases include Campos Novos (Brazil), Barra Grande (Brazil), and Mohale (South Africa), where in some instances these cracks have led to dewatering of the reservoir to allow for the concrete slabs repairs. The development of these fractures may be attributed to the highly deformable rockfill body. In general, the state-of-the-art design of CFRD’s is mostly based on common practice rather than rigorous analysis procedures. And as such, cracking problems because of deformability of the rockfill may not be properly predicted unless a detailed analysis is performed. In this work, a new framework for analysis of CFRD’s is developed that is capable of predicting the possible concrete-facing failure. As a part of this framework, a comprehensive non-linear finite element analysis (FEA) scheme is developed to model the construction sequence, the contact interaction between the concrete facing and the rockfill body, and the impounding of the reservoir. As a case study, using the developed framework, the Kárahnjúkar CFRD (Iceland, 198m height) is analyzed, the results are validated by the field measurements, and mitigation measures suggestions are provided. This methodology, based on the results of the investigation, provides guidelines and establishes a framework for analysis of CFRD’s that can be used for design purposes.. Keywords: CFRD, Concrete Faced, Rockfill, Dam, Finite Element Analysis.
PH.D in Structural Engineering, December 2013
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Title: SYSTEMWIDE INTERSECTION SIGNAL TIMING OPTIMIZATION SIMULTANEOUSLY MINIMIZING VEHICLE AND PEDESTRIAN DELAYS
Creator: Roshandeh, Arash Moradkhani
Date: 2013, 2013-07
Description: The ever-growing traffic volume especially in urban areas stretches the transportation system to be operated at near or exceeding capacity and...
Show moreThe ever-growing traffic volume especially in urban areas stretches the transportation system to be operated at near or exceeding capacity and causes congestion. Expanding system capacity and effectively utilizing available capacity could help reduce traffic congestion. In most of cases, adding extra travel lanes in dense urban street networks is not feasible any more due to land scarcity. This study introduces a new method for signal timing optimization that is carried out by adjusting green splits of AM peak, PM peak, and rest of the day timing plans for each signalized intersection in the network without changing the existing cycle lengths and signal coordination to minimize total vehicle and pedestrian delays per cycle. The proposed method contains a basic model that handles vehicle delays only and an enhanced model that simultaneously addresses vehicle and pedestrian delays using two different pedestrian delay estimation methods. Both models are incorporated into an agent-based regional travel demand forecasting tool for detailed traffic assignments using data on Chicago regional travel demand, traffic counts, geometric designs, and signal timing plans for major intersections in the Chicago Central Business District (CBD) street network. The computational experiment reveals that vehicle delays in the CBD area could reduce by 10 percent when only considering vehicle delays and 5 percent when simultaneously considering vehicle and pedestrian delays for signal timing optimization. Considering the intersections safety analysis, it has been found that signals timing optimization in all four areas combined without considering pedestrian delays decreased different crash types under various severities for multiple vehicle collisions as well as vehicle-pedestrian ones. Taking care of both vehicles and pedestrians delay xvi vii simultaneously, using HCM method, just a very few situations represent slight increases in crash frequencies and all other cases indicate crash reductions. Compared with the sensitivity analysis results using the HCM method for calculating pedestrian delays in the enhanced model applications, the Levinson method produces different results even though crash frequency reduction trends are almost the same as HCM method results.
PH.D in Civil Engineering, July 2013
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