Browsing by Author "Atadero, Rebecca, committee member"

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Open Access
A framework for life-cycle cost optimization of buildings under seismic and wind hazards
(Colorado State University. Libraries, 2014) Cheng, Guo, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Strong, Kelly, committee member
The consequential life and economic impact resulting from the exposure of building structures to single hazards have been well quantified for seismic and wind loading. While it has been recognized that structures are likely to be subjected to multiple hazards during their service life, designing for such scenario has been achieved by as considering the predominant hazard. Although from a structural reliability perspective, this might be a reasonable approach, it does not necessarily result in the most optimal life-cycle cost for the designed structure. Although such observation has been highlighted in recent studies, research is still needed for developing an approach for multi-hazard life-cycle optimization of structures. This study presents a framework, utilizing structural reliability, for cost optimization of structures under wind and seismic hazards. Two example structures, on which the framework is applied, are investigated and their life-cycle cost analyzed. The structures represent typical medium and high rise residential buildings located in downtown San Francisco area. The framework comprises of using the first order reliability method (FORM), programed in MATLAB and interfaced with ABAQUS finite element software to obtain the corresponding reliability factors for the buildings under various loading intensities characterized by the probability of exceedance. The finite element analyses are carried out based on real seismic and wind pressure records using nonlinear finite element time-history dynamic analysis. The random variables selected include hazard intensity (wind load and seismic intensity) and elastic modulus of steel. Once the failure probabilities are determined for the given limit state functions, the expected failure cost for the building service duration considering earthquake or wind hazard, or both, is calculated considering discount rate. The expected life-cycle cost is evaluated using life-cycle cost function, which includes the initial construction cost and the expected failure cost. The results show that the optimal building design considering the wind hazard alone, the seismic hazard alone or a combination of both is different. The framework can be utilized for an optimal design of both wind and seismic load for a given level of hazard intensity.
Open Access
A multi-objective community-level sesimic retrofit optimization combining social vulnerability with an engineering framework for community resiliency
(Colorado State University. Libraries, 2015) Jennings, Elaina N., author; van de Lindt, John W., advisor; Atadero, Rebecca, committee member; Mahmoud, Hussam, committee member; Peek, Lori, committee member
This dissertation presents a multi-objective optimization framework for community resiliency by providing decision maker(s) at the local, state, or other government level(s) with an optimal seismic retrofit plan for their community's woodframe building stock. A genetic algorithm was selected to perform the optimization due to its robustness in multi-objective problem solving. In the present framework, the algorithm provides a set of optimal community-level retrofit plans for the woodframe building inventory based on the socio-demographic characteristics of the focal community, Los Angeles, California. The woodframe building inventory was modeled using 37 archetypes designed to several historical and state-of-the-art seismic design provisions and methodologies. The performance of the archetypes was quantified in an extensive numerical study using nonlinear time history analysis. Experimental testing was conducted at full scale on a three-story soft-story woodframe building. The experimental testing investigated the seismic performance of several retrofit strategies for use in the framework, and the results were used in development of a metric correlating inter-story drift limits with damage states used in the framework. A performance-based retrofit design is presented in detail, and the experimental testing results of four retrofits are provided as well. The algorithm uses each archetype's seismic performance to identify the set of optimal community-level retrofit plans to enhance resiliency by minimizing four objectives: initial cost, economic loss, number of morbidities, and recovery time. In the model, initial cost sums the cost of each new retrofit, economic loss incorporates direct and indirect costs; the number of morbidities includes injuries, fatalities, and persons diagnosed with post-traumatic stress disorder (PTSD); and a recovery time is estimated and may be used to represent the loss in quality of life for the affected population. The framework was calibrated to the estimated losses from the 1994 Northridge earthquake. An application of the framework is presented using Los Angeles County as the community. Two forecasted populations are also examined using the census data for Daly City, California and East Los Angeles to further exemplify the framework. Analyses were conducted at six seismic intensities. In all illustrative examples, the total financial loss (e.g., initial cost + economic loss) was higher for the initial population (i.e. un-retrofitted community). When combining this financial savings with the reduced number of morbidities, it is clear that the higher initial cost associated with retrofitting the woodframe building stock greatly outweighs the risks and losses associated with not retrofitting. The results also demonstrated how retrofitting the existing woodframe building stock greatly reduces estimated losses, especially for very large earthquakes. The resulting losses were further investigated to demonstrate the important role that the mental health of the population plays in a community's economy and recovery following disastrous events such as earthquakes. Overall, the results clearly demonstrate the necessity in including social vulnerability when assessing or designing for community-level resiliency for a seismic hazard.
Open Access
A streamlined bridge inspection framework utilizing unmanned aerial vehicles (UAVs)
(Colorado State University. Libraries, 2019) Perry, Brandon J., author; Guo, Yanlin, advisor; Atadero, Rebecca, committee member; van de Lindt, John W., committee member; Beveridge, Ross, committee member
The lack of quantitative measures and location information for instances of damage results in human-based bridge inspections that are variable and subjective in nature. With bridge owners and managers tasked with making major maintenance/repair decisions with inadequate funding and resources, it is appealing to develop a transparent bridge inspection and evaluation system that integrates field inspection and documentation of damage with quantitative measures and geo-referenced locations in a holistic process. A new, streamlined bridge inspection framework based on unmanned aerial vehicles (UAVs) is proposed to improve the efficiency, cost-effectiveness, and objectivity of these inspections while enhancing the safety of inspectors. Since the current bridge inspection practices use a component based structural rating system, the new UAV-based bridge inspection system should also follow a component-wise damage evaluation system to enable the seamless adoption of this new technology into practice. To provide bridge managers/owners with the streamlined decision-making support, this new system uniquely integrates UAV-based field inspection, automated damage/defect identification, and establishment of an element-wise As-Built Building Information Model (AB-BIM) for the damage documentation in a holistic manner. In this framework, a UAV platform carrying visual sensors first collects data for identifying defects (i.e. cracks, spalling and scaling of concrete). Next, an automated damage detection algorithm is developed to quickly extract quantitative damage information (i.e. type, size, amount, and location) from the data. By using UAV-enabled photogrammetry and unsupervised machine learning techniques, this system can automatically segment the bridge elements (i.e. beam, girders, deck, etc.) from a 3D point-cloud with minimal user input. In the end, the damage information is mapped to the corresponding structural components of the bridge and readily visualized in the AB-BIM. The documented element-wise damage information with quantitative measures in conjunction with the 3D visualization function in the proposed system can provide bridge managers with a transparent condition evaluation and a one-stop decision making support which can greatly ease the planning of repair/maintenance. The feasibility of this approach is demonstrated using a case study of a Colorado bridge.
Open Access
Application of systems engineering principles in the analysis, modeling, and development of a DoD data processing system
(Colorado State University. Libraries, 2023) Fenton, Kevin P., author; Simske, Steven J., advisor; Bradley, Thomas, committee member; Carlson, Ken, committee member; Atadero, Rebecca, committee member
In support of over 1000 military installations worldwide, the Department of Defense (DoD) has procured contracts with thousands of vendors that supply the military with hazardous materials constituting billions of dollars of defense expenses in support of facility and asset maintenance. These materials are used for a variety of purposes ranging from weapon system maintenance to industrial and facility operations. In order to comply with environmental, health, and safety (EHS) regulations, the vendors are contractually obligated to provide Safety Data Sheets (SDSs) listing EHS concerns compliant with the requirements set forth by the United Nations Globally Harmonized System of Classification and Labeling of Chemicals (GHS). Each year chemical vendors provide over 100 thousand SDSs in a PDF or hard copy format. These SDSs are then entered manually by data stewards into the DoD centralized SDS repository – the Hazardous Material Management Information System (HMIRS). In addition, the majority of these SDS are also loaded separately by separate data stewards into downstream environmental compliance systems that support specific military branches. The association between the vendor-provided SDSs and the materials themselves was then lost until the material reaches an installation at which point personnel must select the SDS associated to the hazardous material within the service-specific hazardous material tracking system. This research applied systems engineering principles in the analysis, modeling, and development of a DoD data processing system that could be used to increase efficiency, reduce costs, and provide an automated solution not only to data entry reduction but in transitioning and modernizing the hazard communication and data transfer towards a standardized approach. Research for the processing system covered a spectrum of modern analytics and data extraction techniques including optical character recognition, artificial neural networks, and meta-algorithmic processes. Additionally, the research covered potential integration into existing DoD framework and optimization to solve many long-standing chemical management problems. While the long-term focus was for chemical manufacturers to provide SDS data in a standardized machine-encoded format, this system is designed to act as a transitionary tool to reduce manual data entry and costs of over $3 million each year while also enhancing system features to address other major obstacles in the hazard communication process. Complexities involved with the data processing of SDSs included multi-lingual translation needs, image and text recognition, periodic use of tables, and while SDSs are structured with 16 distinct sections – a general lack of standardization on how these sections were formatted. These complexities have been addressed using a patent-pending meta-algorithmic approach to produce higher data extraction yields than what an artificial neural network can produce alone while also providing SDS-specific data validation and calculation of SDS-derived data points. As the research progressed, this system functionality was communicated throughout the DoD and became part of a larger conceptual digital hazard communication transformation effort currently underway by the Office of the Secretary of Defense and the Defense Logistics Agency. This research led to five publications, a pending patent, an award for $280,000 for prototype development, and a project for the development of this system to be used as one of the potential systems in a larger DoD effort for full chemical disclosure and proactive management of not only hazardous chemicals but potentially all DoD-procured products.
Open Access
Application of systems engineering to complex systems and system of systems
(Colorado State University. Libraries, 2017) Sturdivant, Rick L., author; Chong, Edwin K. P., advisor; Sega, Ronald M., committee member; Jayasumana, Anura P., committee member; Atadero, Rebecca, committee member
This dissertation is an investigation of system of systems (SoS). It begins with an analysis to define, with some rigor, the similarities and differences between complex systems and SoS. With this foundation, the baseline concept is development for several different types of systems and they are used as a practical approach to compare and contrast complex systems versus SoS. The method is to use a progression from simple to more complex systems. Specifically, a pico hydro electric power generation system, a hybrid renewable electric power generation system, a LEO satellites system, and Molniya orbit satellite system are investigated. In each of these examples, systems engineering methods are applied for the development of a baseline solution. While these examples are complex, they do not rise to the level of a SoS. In contrast, a multi-spectral drone detection system for protection of airports is investigated and a baseline concept for it is generated. The baseline is shown to meet the minimum requirements to be considered a SoS. The system combines multiple sensor types to distinguish drones as targets. The characteristics of the drone detection system which make it a SoS are discussed. Since emergence is considered by some to be a characteristic of a SoS, it is investigated. A solution to the problem of determining if system properties are emergent is presented and necessary and sufficient conditions for emergence are developed. Finally, this work concludes with a summary and suggestions for additional work.
Open Access
Assessment of potential impacts of climate change on the integrity and maintenance costs of simply supported steel girder bridges in the United States
(Colorado State University. Libraries, 2019) Palu, Susan Mayumi Kock, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Senior, Bolivar, committee member
Bridges in America are aging and deteriorating, causing substantial financial strain on federal resources and taxpayers' money. Amid several deterioration issues affecting bridges one of the most common and costly is malfunction and deterioration of expansion joints, due to accumulation of road debris between joints, traffic, and weather. Clogged joints in particular prevent the superstructure from expanding when subject to a temperature increase, giving rise to thermal stresses that are not accounted for during the design phase. These additional demands, in the form of combined axial loads and moments, are expected to even worsen considering potential future changes in climate. Herein, a new framework is developed to assess structural vulnerability and estimate maintenance costs for approximately 80,000 simply supported steel girder bridges across the U.S. The approach aims to aid in establishing a priority order for bridge maintenance and offer insights on how to better allocate funds for a large inventory of bridges. The structural vulnerability is quantified in terms of the reduced capacity resulting from axial load and moment interaction on the girder-slab composite. The projected daily maximum temperatures for future years of 2040, 2060, 2080 and 2100 were processed from the coupled climate model GFDL CM3 under three climate scenarios: RCP 2.6, RCP 6.0 and RCP 8.5. The results showed that the most critical regions for all climate scenarios are: Northern Rockies & Plains, Northwest, Upper Midwest and West. In contrast, the less susceptible regions are the Southeast followed by the Northeast. In addition to vulnerability, life cycle cost analysis was conducted considering the evolution of structural condition of each asset along the years through the interaction equation. The results showed that savings on the order of $4.5 billion could be attained when vulnerability-informed maintenance practice is followed as opposed to its conventional counterpart. It was observed that the climate scenario RCP 2.6, which represents greater efforts to reduce anthropogenic climate change, resulted in the smallest maintenance cost. Moderate efforts over emissions RCP 6.0 implies a $600 million increase, while no intervention under RCP 8.5 results in an additional $2 billion cost over the long term.
Open Access
Collapse simulations of steel buildings under fire
(Colorado State University. Libraries, 2016) Qin, Chao, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Kirkpatrick, Allan, committee member
Collapse analysis of steel structures under extreme hazards has been placed on the forefront of research in recent decades. This was primarily motivated by the September 11, 2001, terrorist attacks, which caused the complete collapse of the World Trade Centers (WTCs) including WTC-7. The collapse, attributed mainly to fires resulting from the attacks, raised concerns regarding the level of robustness in steel frames when subjected to fire loadings. While complete collapse of steel buildings under elevated temperature is considered a rare event, as no cases have been reported prior to 9/11, understanding collapse mechanisms of steel buildings under fire conditions can help in developing methods by which future failures can be avoided. One of the main limitations towards evaluating such collapse events is the experimental cost and complexity associated with conducting collapse tests. Numerical simulations, if properly employed, can yield significant dividends in understanding and quantifying structural response under extreme hazards. With the worldwide move toward performance-based engineering, understanding, and quantifying system behavior through advanced numerical simulations, especially during the heating and cooling phases of realistic fire exposures, is essential for establishing proper performance-based provisions for fire engineering that ensure both safe and economical design. To that end, the primary objectives of this research are two folds - 1) to develop a numerical tool that would allow for the evaluation of steel frames under fire loading, or any extreme hazard for that matter, up to and including collapse and 2) to evaluate the demand on steel frames, employing moment frames, braced frames, and gravity frames, under different fire scenarios. These two overarching objectives were realized through the development of advanced numerical models of two 6-story steel-frame buildings with moment frames, gravity frames, and different center bracing systems (one model utilized a concentrically braced frame while the other utilized eccentrically braced frame). The building structures were subjected to two different time-temperature curves and two different fire scenarios. Specifically, the ASTM E119 standard fire curve and the Eurocode 3 parametric fire curve were selected to simulate the fire loadings and were applied independently to the building models under two different contained fire scenarios. The two scenarios included - 1) first floor corner compartment fire and 2) whole first floor fire. This allowed for the assessment of different global system response where collapse is triggered by twist of the entire structure accompanied by lateral deformation in the case of a corner compartment fire and progressive vertical displacement of the entire system in the case of the whole first floor fire. The simulation results of this study show that structural response of steel buildings including collapse mechanism and behavior of structural members and connections during fire events can be predicted with reasonable accuracy using advanced numerical finite element analysis. The results provide substantial insight on the behavior of steel building systems under elevated temperature including the potential for system collapse.
Open Access
Comparative life cycle assessment (LCA) and life cycle cost analysis (LCCA) of precast and cast-in-place buildings in United States
(Colorado State University. Libraries, 2020) Vasishta, Tanmay, author; Mehany, Mohammed S. Hashem M., advisor; Killingsworth, John, committee member; Atadero, Rebecca, committee member
Precast construction is one of the growing construction methods for buildings across United States. Many tools have been used to assess environmental and economic impacts of the buildings. LCA and LCCA are one of the most widely used tools to evaluate the environmental and economic impacts of the buildings for their complete life cycle. The research aims to understand the life cycle environment impacts and costs over the complete life cycle for precast and cast-in-place building system. Cradle-to-grave approach was used to develop a framework for assessing the these impacts for precast and cast-in-place building systems constructed in United States through Open LCA software and NIST handbook for LCCA. The environmental impacts and costs associated with the four phases (raw material extraction and manufacturing, installation/construction, operation and demolition) of a precast building in United States were calculated and compared to cast-in-place building system. The research findings implicated that precast using sandwich panel building system had 21% lower life cycle costs (LCC) compared to cast-in-place building system. The construction phase and operation phase also had 38 % and 24% lower LCC compared to cast-in-place building systems. Additionally, lower life cycle environmental impacts towards nine environmental impact indicators were recorded for precast building systems. This study concluded that precast methodology has lower life cycle environmental and economic impacts than cast-in-place and is more sustainable construction method. The developed framework for LCA and LCCA could be applied to all concrete construction projects across the world and could be used as platform for conducting future LCA and LCCA studies as well. The research can also be used by practitioners to understand the phase-wise and total life cycle environmental and economic impacts of precast and further investigate to reduce these impacts.
Open Access
Coupled static fields in magneto-electro-thermoelastic spheres
(Colorado State University. Libraries, 2016) Divya, S. L. Dinavahi, author; Heyliger, Paul R., advisor; Atadero, Rebecca, committee member; Holland, Troy, committee member
Smart/ intelligent materials form an integral part of adaptive and structural systems that have the capability to modify their material properties under the application of ex-ternal stimuli. This study focuses on a laminated layered hollow sphere with a multi- eld coupled material composed of piezo-electric and piezo-magnetic phases. When combined, these configurations create new features and properties that are absent in their constituents. The analysis of these materials requires careful consideration of the effects of interaction of the multi-field effects. In particular, the behavior of the field variables through laminate thickness is of primary interest. In this research, a discrete-layer model is presented and applied to layered anisotropic spheres under the coupled effects of elastic, electric, magnetic, and steady-state temperature fields to study its static behavior. The model is developed in spherical coordinate system based on discrete-layer lamination theory that solves the weak form of the governing equations for the individual fields and specific boundary conditions. The through-thickness behavior of the hollow sphere was investigated by introducing Ritz-based approximations to each of the fields, which are represented layer-wise in the radial direction of the hollow sphere. The accuracy of the model is determined by comparing the results to those of exact solutions. The model is further investigated for effect of three-layer laminate scheme under various surface conditions and new results are presented for the effect of imposed thermal fields.
Open Access
Customer and system impacts of grid support functions for voltage management strategies
(Colorado State University. Libraries, 2020) Giraldez Miner, Julieta, author; Suryanarayanan, Siddharth, advisor; Atadero, Rebecca, committee member; Yang, Liuqing, committee member; Young, Peter, committee member; Zimmerle, Daniel, committee member
This document describes modeling techniques and methods to study the impacts to the utility and to the customer of using DERs such as advanced inverters to provide voltage support in order to maintain voltage within the recommended voltage limits. For this, a method for accurately representing secondary circuits in distribution feeders is proposed and quasi-static-time series (QSTS) simulation techniques are used to study the impact of advance inverter functions to the utility for managing voltage and to the customer in terms of possible generation curtailment. This dissertation looks at factors in medium and low-voltage circuit topology that drive customer voltages with DERs, and investigates where along the distribution feeder are voltage based advance inverter grid support function most effective. The described modeling techniques and methods have informed policy and regulatory type decisions such as updating DER interconnection tariffs and standards.
Open Access
Determining the items that structure bridge management components and their relative weights
(Colorado State University. Libraries, 2012) Johnson, Joshua F., author; Ozbek, Mehmet Egemen, advisor; Clevenger, Caroline, committee member; Atadero, Rebecca, committee member; Chen, Suren, committee member
Ensuring the optimal allocation of available resources between competing bridges is difficult, especially when considering a combination of factors such as continual age related deterioration, ever-increasing traffic demands, and limited resources to address preservation and improvement needs. Optimally allocating funding is crucial since bridges are an essential and expensive component of transportation networks. Bridge Management Systems (BMSs) are commonly used tools that aid managers and decision makers in establishing methods for optimizing available resources and determining how to distribute funds between competing bridges. Recently, NCHRP Synthesis 397 Bridge Management Systems for Transportation Agency Decision Making investigated how transportation agencies are using BMSs and the current state of bridge management practices. The report identified concerns of inadequacy and ineffectiveness with bridge management practices that base decisions solely on single value assessments such as Pontis' Bridge Health Index or the Sufficiency Rating, as found in the federally mandated National Bridge Inspection Standards. Given the critiques in the NCHRP report and other literature related to bridge management, it is evident there exists a need to pursue and develop alternative bridge management practices and systems. The overall purpose of this research is to investigate the concept of isolating the items used to make up a single rating or index in an effort to categorize them under distinct bridge management components such as structural condition, impact on public, and hazard resistance. Each bridge management component has a defined objective as follows: • Structural Condition - accurately access the structural adequacy of a bridge. • Impact on Public - evaluate how bridge attributes affect the traveling public. • Hazard Resistance - evaluate how bridge attributes and external factors affect the vulnerability of a bridge concerning the probability of an extreme event as well as the probability of failure during that event. The specific objectives of this research are (i) to identify the appropriate items that make up each of the aforementioned components and (ii) to determine the relative importance of those items as represented by weighting factors. To achieve these objectives, the researcher conducted a two-part survey seeking input from key bridge management personnel from State DOTs, the Federal Highway Administration (FHWA), and other industry professionals and experts. The first part of the survey identified the appropriate items and the second part determined the relative importance of those items using a mathematical method called the Analytic Hierarchy Process (AHP). The primary contribution of this research is to provide bridge management engineers and decision-makers with effective bridge management components, with well-defined objectives and related items, which clearly identify and distinguish differences in bridge attributes that may go unnoticed when using a single rating or index. This will especially be useful for State DOTs and local agencies, like the Wyoming Department of Transportation, from which the motivation for this research was adapted, who are developing BMSs and methods customized to their particular needs. Upon establishing the bridge management components, by determining the items that make up the components and their relative weights, transportation agencies may utilize them in a variety of ways to conduct multi-criteria decision analyses that complement their current bridge management practices, which in turn may better illustrate the operation of bridges in their system. The total number of respondents was 47, of which 32 were from 29 different State transportation agencies. Of the 47 participants, only 27 contributed to the second part of the survey. A major finding of this research was a result of several participant remarks about with quantifying preservation and maintenance demands through the addition of a fourth bridge management component. The preservation and maintenance component encompasses items that are bridge elements, but may not contribute to the structural capacity of a bridge. Given the degree of influence of adding a fourth component, further research is recommend to confirm these findings and conclusions with a refined two-part survey similar to this research study and possibly interviews or focus groups.
Open Access
Development of a framework to determine the relative weights of contextual factors for complex highway projects
(Colorado State University. Libraries, 2017) Sinha, Akanksha, author; Ozbek, Mehmet E., advisor; Strong, Kelly C., committee member; Atadero, Rebecca, committee member
Traditional project management strategies for highway projects originated with the advent of new construction during the 1950s and 1960s focusing on three dimensions of complexity i.e. cost, schedule and technical (scope). But recently with the major focus shifting towards reconstruction/ rehabilitation projects, the project management strategies also need to shift to include other dimensions rather than perceiving them as risks. A paper by Winter and Smith (2006), "Rethinking Project Management", introduced five new directions to consider while preparing a risk management strategy for complex projects. Following this, a research was conducted by the Second Strategic Highway Research Program, R-10, to study the factors that impact the construction of complex highway projects. The primary outcome of the R-10 study was a five-dimensional approach to project management planning (5DPM) that adds context and financing as two new dimensions to the traditional dimensions of cost, schedule, and technical. Experience during the pilot testing of the 5DPM implementation suggested that the most complicated dimension to assess during the project management planning phase for a complex project is the context dimension which refers to the external factors that have an impact on the project and are difficult to predict and plan for before the start of the project. Currently there is no structured process for evaluating these factors and they are mostly perceived as risks. The R-10 research team identified 8 factor categories which are: stakeholders, project-specific demands, resource availability, environmental, legal and legislative requirements, global and national events, unusual conditions and localized issues and 26 factors under these categories which can cause complexity. The research developed a framework to identify the contextual factors relevant to each specific project and determine the relative weights of these contextual factors using a well-structured approach, the Analytical Hierarchy Process (AHP). Two complex projects within the state of Colorado, U.S. 34 Rebuild and I-25 North Expansion project, were chosen to illustrate the implementation of the developed framework. The primary reason for selecting AHP method was the requirement of pairwise comparison of intangibles derived through the judgement of the experts in a structured mathematical method. The Group AHP was further performed to develop the overall ranking of the contextual factors as a group. The major finding of this study was that as a group, the US 34 Rebuild team valued procedural laws and land acquisition as the most important factor followed by work-zone visualization and marketing and public relations. For the I-25 team, the most important factor was procedural laws followed by limitations and constraints and project management capabilities. The most striking difference between the factor weights for both the projects was that the weights were more evenly distributed between factors for US-34, whereas for I-25, few factors had very high weights while few others had exceptionally low weights. This framework will enable the project management teams of complex highway projects to determine the relevant weights of the factors during the project management planning phase which can help them in making important decisions at the early stages of the project. Through the development of this framework, this study helps transportation agencies identify the contextual factors and prioritize them right from the start in a structured manner rather than perceiving them as risks for their projects.
Open Access
Development of improved redundancy measure for the Colorado State Highway System
(Colorado State University. Libraries, 2022) Bui, Kenny, author; Jia, Gaofeng, advisor; Atadero, Rebecca, committee member; Shakouri, Mahmoud, committee member
The Colorado Department of Transportation (CDOT) has been working to improve the resiliency of its transportation system and facilities. A vital attribute of a resilient transportation system is whether or not the system has redundancies built into it. For example, if a roadway is closed to traffic, but there are alternative routes for the drivers to take, then the closed roadway could be considered to have redundancy. The current redundancy measure that CDOT uses is based on the number of other state highways that connect to a particular highway. The redundancy measure needs refinement because it does not consider the additional travel time and distance from the alternative routes. This research aims to develop an improved method for measuring the redundancy of state highway facilities in Colorado. To establish information on the number of detours (i.e., alternative routes) for a specific road segment and the additional travel time and distance on each of the detours, detour analyses are carried out to identify (if any) the first, second, and third best alternative detours for all the highway segments in the state highway system. This is realized by closing the corresponding road segment or alternative routes, updating the transportation network, and rerunning the traffic analysis on the updated transportation network. For more accurate traffic analysis, the combined distribution and assignment model is used to take into account the effects of congestion on the traffic flow. Because the full transportation network in CDOT's state-wide model has large number of nodes and links, to reduce the computational effort for the detour analysis (which needs to be repeated for all road segments), an aggregated network based on the full network is developed and used for detour analysis for cars. Separate detour analyses are also carried out for the freight vehicles since they use a separate freight network, which is a subnetwork of the aggregated network. In the end, using the information from the detour analyses, a new improved redundancy metric is developed that takes into account not only the number of alternative routes for a road segment but also the additional time and distance on the alternative routes. The new redundancy metric also incorporates a weight for each best detour (e.g., the first, second, and third best detours are weighted differently). The detour information will be used to update the existing CDOT Detour Identification Tool. The redundancy metric can be further used to calculate and update CDOT's criticality score to determine the resiliency of the Colorado State Highway System and guide activities to enhance its resilience.
Open Access
Differences for employees who use BIM/VDC in the construction workplace
(Colorado State University. Libraries, 2014) Inguva, Girija, author; Clevenger, Caroline, advisor; Ozbek, Mehmet, committee member; Atadero, Rebecca, committee member
There is growing recognition across the US construction industry for the benefits of organizational adoption of Building Information Modeling, also referred to as Virtual Design and Construction (BIM/VDC). One of the key factors that enables successful organizational adoption of new technologies is the adoption of these technologies by key participants, in this case by BIM employees. Their positive experiences at their current organization determine their continuation on a BIM/VDC path, thus leading to consistent organizational adoption and negative experiences could mean that they migrate from a BIM career to a Non-BIM career or to another organization to seek better experiences. This research aims to study the perceptions of BIM employees as compared to the perceptions of Non-BIM employees in the construction industry in four key categories: work life balance, career advancement, workplace experience and skill levels. An online survey is used and responses are compared first using averages and then using Pearson's X2 or Fisher's probability test to test for statistical significance where applicable. Differences inform us of the advantages or challenges of a BIM/VDC career at an individual level. Additionally, differences between men and women are also studied, along with differences between BIM employees from organizations with a separate BIM/VDC department and BIM employees from organizations without a separate BIM/VDC department. The general trends observed in terms of averages indicate that BIM/VDC personnel are generally more satisfied with their jobs and consider common barriers to career advancement to be of lesser relevance than their Non-BIM counterparts. The fact that most differences are not statistically different also suggests that BIM employees may not be treated that differently from Non-BIM employees. Of all groups, the most positive perceptions are reported by male BIM respondents from organizations without separate BIM/VDC departments.
Open Access
Digital twins for structural inspection, assessment, and management
(Colorado State University. Libraries, 2023) Perry, Brandon J., author; Guo, Yanlin, advisor; Atadero, Rebecca, committee member; van de Lindt, John, committee member; Mahmoud, Hussam, committee member; Ortega, Francisco, committee member
With the rapid advancements in remote sensing, uncrewed aircraft systems (UAS), computer vision, and machine learning, more techniques to maintain and evaluate the performance of the built infrastructure become available; however, these techniques are not always straightforward to adopt due to the remaining challenges in data analytics and the lack of executable actions that can be taken. The paper proposes a Digital Twin, which is a virtual representation of structures and has a myriad of applications to better assess and manage civil infrastructure. The proposed Digital Twin includes the techniques to store, visualize, and analyze the data collected from a UAS-enabled remote sensing inspection and computational models that support decision-making regarding the maintenance and operation of structures. The data analysis module identifies the location, extent, and growth of a defect over time, the structural components, and connections from the collected image with artificial intelligence (AI) and computer vision. In addition, the three-component (3C) dynamic displacements are measured from videos of the structure. A model library within the digital twin to assess the structure's performance, which includes three types of models, is proposed: 1) a visualization model to provide location-based data query, 2) an automatically generated finite element (FE) model as a basis for simulation, and 3) a surrogate model which can quickly predict a structure's behavior. Ultimately, the models in the library suggest executable actions that can be taken on a structure to better maintain and repair it. A discussion is presented showing how the Digital Twin can assist decision-making for structural management.
Open Access
Effect of fire and fire following an earthquake on steel reduced beam section moment connections
(Colorado State University. Libraries, 2013) Turbert, Collin, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, committee member; Kirkpatrick, Allan, committee member
The main objective of this research is to investigate the behavior of steel frames with reduced beam sections (RBS) during a fire as well as during the combined events of fire following an earthquake (FFE). Historical events and recent disasters have clearly demonstrated that the occurrence of these two events (fire and FFE) within steel framed buildings represents a probable scenario that warrants further investigation. Accurate analytical evaluation of the structural behavior of steel buildings under fire, and to a lesser extent an earthquake, is difficult due to the many complex and uncertain phenomena involved. Detailed numerical modeling of the overall structural system has been shown to provide the most reliable simulation results under current research development. However, detailed analysis is generally computationally expensive and as such not practically applicable. In addition, the nonlinear behavior of entire structures is complex and not fully understood. Therefore, detailed numerical models of the overall structural system often have difficulty capturing local failure modes. This research provides a practical analytical approach to perform accurate numerical evaluation of steel structures under fire and FFE and to closely investigate its characteristic behavior. The approach utilized is to limit the focus on localized compartment fires and investigate the behavior of a single beam-column subassembly within the chosen compartment. By limiting the focus of the study the numerical models can be simplified by utilizing specifically appropriate subassembly models for the analysis. Using the finite element program ABAQUS, two different beam-column subassemblies with RBS were created and analyzed. The subassemblies are representative of actual connections in two steel special moment resisting frames that were designed for the highly seismic Los Angeles region. The frames selected for analysis are an 8-story 4-bay frame and a 16-story 4-bay frame and the selected subassemblies are located at the exterior of the frames at the mid and lower levels, respectively. Both subassemblies were analyzed under fire alone to determine their structural behavior during the event as well as allow for a better understanding of the influence the seismic demand has on the behavior of the connection when exposed to FFE. For the FFE simulations both models were analyzed under a suite of earthquake ground motions followed by a fire simulation. For the fire analysis portion of both simulations (fire alone and FFE) a sequentially coupled thermo-mechanical modeling technique, which includes representative constraint elements to simulate the restraint imposed by the frame is employed. The results of the study highlight the significance of including realistic boundary conditions during fire simulations and points towards the possibility for the occurrence of substantial damage in unprotected steel frames during fire as well as protected steel frames during fire following an earthquake.
Open Access
Effect of mixed-mode loading on fatigue and fracture assessment of a steel twin box-girder bridge
(Colorado State University. Libraries, 2019) Irfaee, Mazin M., author; Mahmoud, Hussam, advisor; Heyliger, Paul, committee member; Atadero, Rebecca, committee member; Stright, Lisa, committee member
Steel twin box-girders are considered an attractive option for the construction of bridges due to their basic design, simple form, and ease of creation. Despite their advantages, they are considered fracture critical and as such there is an additional mandate for these bridges to inspected more in depth. This causes their inspection cost to be approximately two to five times greater than that of bridges with non-fracture critical members. The required additional inspection in the U.S. is mainly driven by rare historical events of bridge collapse for bridges that were not steel twin box girders. In addition, the mandated additional inspection does not reflect the inherent level of redundancy in most bridges. Therefore, it is important to quantify the potential for fracture and the level of redundancy in steel two-girder bridges in general, and twin box girders in particular, to minimize their inspection cost. Recognizing the inherently large scatter in fatigue performance, evaluating crack propagation and potential for fracture should, however, be performed in a probabilistic manner using detailed models that represent accurate behavior of the bridge. In this study, a detailed numerical finite element model of steel twin tub-girder bridge is developed and crack growth analysis, potential for fracture of its main tubs, and its overall redundancy is evaluated. The crack growth analysis is performed using multi-mode linear elastic fracture mechanics while accounting for uncertainties in the random variables associated with crack propagation and fracture. The results of the crack growth analysis are utilized to develop fragility functions that specify inspection intervals versus probability of failure where failure is characterized by dynamic crack growth. The analysis conducted to quantify the potential for fracture show distinct possible failure modes that vary from brittle fracture to ductile fracture. The extreme loading case shows that the bridge overall is not at risk of collapse. It is important to note that this conclusion cannot be generalized for all tub girder bridges since the level of redundancy is expected to vary between bridges depending on many factors such as girders geometries, plate thickness, fabrication, among others. However, the presented approach and the corresponding results provide a systematic way by which fracture critical bridges can be evaluated.
Embargo
Engineering in practice: from quantitative biology modeling to engineering education
(Colorado State University. Libraries, 2024) Weber, Lisa, author; Munsky, Brian, advisor; Atadero, Rebecca, committee member; Prasad, Ashok, committee member; Reisfeld, Brad, committee member
In quantitative analyses of biological processes, one may use many different scales of models (e.g., spatial or non-spatial, deterministic or stochastic, time-varying or at steady-state) or many different approaches to match models to experimental data (e.g., model fitting or parameter uncertainty/ sloppiness quantification with different experiment designs). These different analyses can lead to surprisingly different results, even when applied to the same data and the same model. In Chapters 2, a variety of modeling approaches that can be utilized in analyzing biological processes are explained, with examples included of how to mathematically represent a system in order to use these various modeling approaches. Many of these mechanistic modeling approaches are demonstrated in Chapter 3 when we use a simplified gene regulation model to illustrate many of the concerns regarding modeling approach differences; these include ODE analyses of deterministic processes, chemical master equation and finite state projection analyses of heterogeneous processes, and stochastic simulations. For each analysis, we consider a time-dependent input signal (e.g., a kinase nuclear translocation) and several model hypotheses, along with simulated single cell data, to illustrate different approaches (e.g., deterministic and stochastic) in the identification of mechanisms and parameters of the same model from the same simulated data. We also explore how uncertainty in parameter space varies with respect to the chosen analysis approach or specific experiment design, and conclude with a discussion of how our simulated results relate to the integration of experimental and computational investigations to explore signal-activated gene expression models in yeast [1] and human cells [2]. Different modeling approaches are used in Chapter 4 to build on the work of Scott, et al. (2018, 2019) [3, 4] to evaluate different model classes for DNA structural conformation changes, including the unwinding/rewinding dynamics of the double-stranded DNA (dsDNA) helical structure and subsequent binding interactions with complementary single-stranded oligonucleotides probes (oligos), in relation to different conditions: temperature, salt concentration, and the level of supercoiling of the DNA molecule. This is done to identify a class of models that best fit the DNA unwinding and subsequent oligo probe binding experimental data as a function of these three conditions. In this work, we demonstrate the use of additional quantitative modeling approaches, including a modified genetic algorithm along with the process of cross validation and Markov Chain Monte Carlo (MCMC) simulations with the Metropolis-Hastings (MH) algorithm [5] to explore parameter space. We also demonstrate many of the challenges that can be encountered when modeling complex biological phenomena with actual experimental data. Although much of the work described in Chapters 2 through 4 may appear to be, on the surface, just the use of various computational methods for biological processes to increase understanding of biological mechanisms, much of it also has a separate purpose. The structure of these works and an underlying aim of much of this work, namely Chapters 2 and 3, is to provide guidance with examples to make these computational approaches more accessible to scientists and engineers. Many of these approaches are included in a quantitative biology (UQ-bio) summer school that has been conducted for the last few years as well. Through the process of developing these works and seeking to make quantitative biology more accessible, a related goal manifested to improve the accessibility of engineering education as a whole, which is addressed in Chapter 5, specifically related to diversity, equity, and inclusion (DEI) in undergraduate engineering education. There have been efforts since Fall 2017 to increase the presence of DEI in the undergraduate CBE education using a bottom up approach. To date, various efforts have been incorporated into the first two years of the CBE program. In Chapter 5, these previous efforts, along with lessons learned, are detailed. A substantial, holistic approach to incorporating DEI throughout the CBE curriculum is proposed, based on a review of recent work by other engineering education researchers, to help the CBE department create a more inclusive educational experience for undergraduate students and better enable students to handle the complex challenges they may face in their careers.
Open Access
Examining students' systems thinking in a natural resources management capstone class
(Colorado State University. Libraries, 2016) Casper, Anne Marie Aramati, author; Balgopal, Meena, advisor; Fernandez-Gimenez, Maria, advisor; Schultz, Courtney, committee member; Atadero, Rebecca, committee member
Critical Literature Review Humans undisputedly dominate Earth’s ecosystems, therefore we need to move beyond 'human-free' conceptions of ecosystems. However, there is a lack of consensus about how humans, our influence, and our social systems fit within ecosystems, and several different terms, such as social-ecological system, are now used to describe integrated systems. The current proliferation of terms and lack of shared meaning causes problems for interdisciplinary researchers as well as students. I propose that our language needs to catch up with our conceptions, and that ‘ecosystem’ needs to be explicitly defined to include humans, our impacts, and our social systems. Research Manuscripts Natural resource management (NRM) decisions have far reaching implications for global ecological change. Because beliefs influence decisions, it is vital that the NRM curriculum reflects the shift to include humans as integrated components of ecosystems to facilitate effective future NRM, however no appropriate metric exists for assessment. Additionally, there is a concern that NRM students are not graduating with well-developed systems thinking, communication, and group work skills. Social-ecological systems (SES) are linked social and ecological systems, and graduates who are able to consider a SES as a whole are better able to address the complex problems in NRM. I framed my research through the intersection of socio-cultural and conceptual change theories. Socio-cultural theory states that each individual’s knowledge and experiences influence how they learn, and conceptual change theory describes the process individuals go through to replace existing conceptions with new conceptions. The intersection of these lenses imbeds conceptual change within an individuals’ experiences and knowledge. My guiding question was: how do students' conceptions of systems thinking change during a one-semester capstone class? Specifically, How do 1) students describe their conceptions of social-ecological systems and resilience as changing over the course of an NRM capstone course, and what do they think helped change them? 2) NRM students situate humans in relation to ecosystems, and more specifically, to the term, ecosystem? 3) NRM students revise their conceptions of 'ecosystem' over the course of their capstone course? I used phenomenological and grounded theory qualitative research approaches to study the Spring 2014 and 2015 NRM capstone classes at a large research university in the United States. I interviewed students, collected all coursework for analysis, audio recorded lectures, and obtained copies of all lecture presentation materials for analysis. In my phenomenological study (n=3) I found that students' conceptions of social and biophysical systems became more integrated, and their ideas about systems thinking and resilience broadened to encompass greater complexity. These conceptual shifts were influenced by interactions with other students, natural resource professionals, and stakeholders during class and their semester-long group project. However, some students still held under-developed conceptions of ecosystems, which became the focus of the following two study manuscripts. From student responses (n=20) and the course context I developed a continuum of human relationships to ecosystems for my metric to address question two: i) exclusion, ii) uncertain-exclusion, iii) uncertain, iv) uncertain-inclusion, and v) inclusion. My continuum provides a useful tool to help unpack the complexity of the human-environment relationship conception, which is a part of the ecological literacy construct. To address research question three I used my continuum to identify how students' conceptions changed. I found that students' definitions of the relationships between natural and ecosystem, human, and human artifact influenced their conceptions of ecosystems. Students who did not describe ecosystems as natural struggled much less with an integrated human-ecosystem conception than those who described ecosystems as natural. My overarching findings indicate that students can and do experience conceptual change throughout their capstone course. However, I found that students' conceptions and conceptual shifts were not always consistent with the material presented in the class. Therefore, it is important to teach from a constructivist standpoint (that each individual builds their own meaning of the world, which is influenced by their prior knowledge and experiences), and explicitly co-construct meaning in the classroom.
Open Access
Experimental fatigue evaluation of underwater steel panels retrofitted with fiber reinforced polymers
(Colorado State University. Libraries, 2019) Hudak, Lauren, author; Mahmoud, Hussam, advisor; Riveros, Guillermo, committee member; Atadero, Rebecca, committee member; Arneson, Erin, committee member
Many steel structures are susceptible to fatigue loading and damage that can potentially threaten their integrity if not monitored and repaired. Steel hydraulic structures (SHS), in particular, experience fatigue loading during operation and are exposed to harsh environmental conditions that can further reduce fatigue life through mechanisms such as stress corrosion cracking and corrosion fatigue. Dewatering to complete inspections or repairs to SHS is time consuming and leads to economic losses, and current repair methods, such as rewelding, often cause new cracks to form after relatively few cycles, requiring repeated inspection and repair. The use of bonded carbon fiber reinforced polymer (CFRP) to repair fatigue cracks in metallic structures has been successfully demonstrated in other industries, and recent work has suggested that the method can also offers a more reliable repair method for SHS. The very few studies regarding CFRP retrofits of SHS indicate that early bond failure often controls the degree of fatigue life extension provided by the repair. This study aims to extend previous experimental studies and further increase the fatigue life of repaired steel components by employing methods to improve CFRP bonding. Additionally, the use of basalt reinforced polymer (BFRP) as an alternative to CFRP is proposed. Limited examples of BFRP used in structural applications are available, but BFRP is attractive for SHS because it does not react galvanically with steel as CFRP does. In this study, four large-scale center-cracked panels were tested under constant amplitude fatigue loading. Of the four specimens, one was retrofitted with CFRP, and one was retrofitted with BFRP. To achieve an environment similar to that experienced by SHS, the two retrofitted specimens and one unretrofitted specimen were submerged in fresh water during testing. Remaining fatigue life was used as the primary metric for assessing the efficacy of the retrofit method. Results indicated that the use of both CFRP and BFRP are effective at extending fatigue life. The extent of fatigue life extension was still controlled by the quality of the FRP bond to steel; however, bond behavior was improved in comparison to previous underwater applications.