Mountain Scholar :: Browsing by Author "Atadero, Rebecca, advisor"

Browsing by Author "Atadero, Rebecca, advisor"

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Open Access
Chloride binding and desorption mechanism in blended cement containing supplementary cementitious materials exposed to de-icing brine solutions
(Colorado State University. Libraries, 2024) Teymouri Moogooee, Mohammad, author; Atadero, Rebecca, advisor; Fantz, Todd, advisor; Jia, Gaofeng, committee member; Bailey, Travis, committee member
Concrete, the most widely used construction material globally, faces significant challenges due to its porous nature, particularly from chloride-induced corrosion. This corrosion, primarily caused by chloride ions penetrating concrete, affects over 7.5% of U.S. concrete bridges, incurring annual costs ranging from $5.9 to $9.7 billion. Chlorides enter concrete from various sources, including de-icing salts. Maritime infrastructures also suffer from severe chloride-induced corrosion because seawater contains a high concentration of chloride ions. Irrespective of how chlorides enter the concrete, chlorides can exist in concrete in two forms: free and bound chlorides. While bound chlorides are beneficial, they can be released due to environmental factors like carbonation and chemical attacks, exacerbating corrosion rates. These attacks cause pH reduction in concrete and subsequently can result in the release of bound chlorides (chloride desorption).This dissertation aims to address three main objectives: (1) investigate factors influencing chloride binding measurements due to lack of a standardized method for chloride binding measurements, (2) study chloride desorption mechanisms in different cementitious systems exposed to de-icing brines, and (3) analyze pH and compositional changes in blended pastes under chloride contamination and carbonation. First, factors impacting chloride binding measurements were identified, such as sample form and saturation level, solution composition, and solution volume. Vacuum-saturated samples exhibited higher chloride binding than partially saturated or dried samples, with powdered samples showing the highest binding. Secondly, chloride desorption mechanisms were investigated in both Ordinary Portland Cement (OPC) pastes and pastes containing supplementary cementitious materials (SCMs) like fly ash, slag, and silica fume. Results indicated that the type of cation in the brine solution influenced bound chloride levels, with SCMs improving chloride binding capacity. Slag inclusion was effective in promoting chloride binding, while silica fume showed the least effect. The degree of chloride desorption under acid attack depended on the acid-to-paste mass ratio. The results reveal that inclusion of fly ash and slag is favorable in terms of chloride desorption, and silica fume is not recommended for use when chloride-induced corrosion is a concern. MgCl2 and CaCl2 de-icers demonstrated a lower chloride desorption compared to NaCl. Finally, the synergistic effects of chloride contamination and carbonation were examined in OPC and fly ash-containing pastes. Carbonation led to over 95% chloride desorption after two weeks, with fly ash-containing pastes exhibiting lower pH levels due to reduced portlandite content. Incorporation of fly ash is not recommended when carbonation is a concern. Therefore, caution should be exercised when considering fly ash inclusion in mixtures where both chloride contamination and carbonation are simultaneous concerns. This dissertation contributes to understanding chloride desorption in cementitious systems, essential for enhancing the durability and service life of concrete structures. This dissertation shed lights on primary factors influencing chloride binding measurements, enhancing the accuracy and comparability of chloride binding results. The results reveal that type of cation present in the solution and type of SCMs have significant influences on the pH, chloride binding capacity, and chloride desorption rates.
Open Access
Evaluating the bond durability of FRP-concrete systems subjected to environmental exposures
(Colorado State University. Libraries, 2012) Mata Carrillo, Oscar Rafael, author; Atadero, Rebecca, advisor; Heyliger, Paul, committee member; Glick, Scott, committee member
The poor current condition of transportation infrastructure in the U.S. is well documented. With traffic volumes on the rise, as well as limited funding available to maintain and rehabilitate aging bridges, cost effective means of improving the performance and durability of these structures must be employed. Fiber Reinforced Polymers (FRPs) offer one potential solution. Their use has been progressively growing in the field of civil engineering as the material's high strength to weight ratio, non-corrosive nature, and ability to conform to existing geometry make it appealing in the reinforcement of existing reinforced concrete structures. In most applications of FRP to strengthen an existing structure, the FRP-concrete bond is essential. Bond is needed for proper transfer of stresses among interfaces. From a durability standpoint, the long-term bond performance is also a major concern. As a result, a long-term durability study was conducted in the laboratory to evaluate the behavior of the bond between the FRP and concrete. Small concrete specimens were prepared, reinforced with FRP material, and subjected to various environmental scenarios such as wet-dry cycles, freeze-thaw cycles, and constant immersion in water, as well as deicing agents. Direct tension pull-off tests and three-point flexural tests were conducted on these specimens to determine any degradation in bond strength over time. Finally, the pull-off test method was evaluated by means of previous research studies and recommendations about preparation procedures were made.
Open Access
Evaluating the long-term durability of fiber reinforced polymers via field assessments of reinforced concrete structures
(Colorado State University. Libraries, 2011) Allen, Douglas Gregory, author; Atadero, Rebecca, advisor; Heyliger, Paul R., committee member; Radford, Don, committee member
Fiber Reinforced Polymer Composites (FRP) are an attractive repair option for reinforced concrete structures, however their long term performance in field environments is not well understood. Laboratory durability tests have indicated that FRP generally performs quite well, but these laboratory tests cannot model the synergistic effects that occur when the FRP is in-service on a bridge (or other structure). Field assessments of FRP properties are very rare in the literature. This thesis describes an effort to collect in-situ data about a FRP repaired concrete arch bridge. The Castlewood Canyon Bridge on Colorado state highway 83 was reconstructed in 2003. The reconstruction included replacement of the deck and spandrel columns and repair of the existing concrete arches with externally bonded FRP. The FRP had been in service for 8 years when its condition was assessed for this project. Assessment efforts started with collection of as much information as possible about the materials and techniques used for repair. Unfortunately only limited amounts of initial or baseline data were recovered. Based on available information a tentative plan for site assessment activities was prepared, including testing locations at the base and crest of the arch. The field assessment of the bridge was completed on location during July, 2011. The complete extrados of the east arch was inspected for voids between the concrete and FRP using acoustic sounding and thermalgraphic imaging. Voids that were previously identified during a routine bridge inspection in 2007 had grown significantly larger by the 2011 assessment. Pull-off tests were used to test the bond strength at the base and top of the arch. Pull-off strengths were on average lower and represented different failure modes from pull-off tests conducted at the time of repair. Large debonded regions of FRP were cut from the structure to use in laboratory testing. Damaged regions were repaired with new FRP. Materials brought back from the bridge were used for tensile and Differential Scanning Calorimetry (DSC) testing. The tensile tests showed that the FRP strength was well below the specified design strength, but the lack of initial data makes it difficult to tell if the material has deteriorated over time, or if the material started off with lower strengths due to field manufacture techniques. The DSC tests showed that the glass transition temperature of the composites was near the value suggested by the manufacturer. The field assessment was used as a case study in collecting durability data about FRP. From this case study numerous recommendations are made to improve the available information about the durability of FRP repairs in field environments. A specific process to be followed in collecting this data is also proposed.
Open Access
Evaluation of new reactive FRP reinforcement assemblies for reinforced concrete transportation structures
(Colorado State University. Libraries, 2014) Bright, Christopher, author; van de Lindt, John W., advisor; Atadero, Rebecca, advisor; Radford, Donald, committee member
This thesis evaluates two new glass-fiber reinforced polymer concrete reinforcement systems which have been designed to serve as a non-corrosive alternative to steel reinforcement in reinforced concrete bridge girders. Due to the nature of the reinforcement geometry, these systems react in a way to introduce compressive confinement into the concrete in the inner regions of the system units. The introduction of this compressive confinement zone will increase particle interaction effects which results in increased shear and tensile force resistance contributed by the affected concrete. The system is also well integrated into the surrounding concrete matrix, therefore eliminating the potential for debonding failures. A proof of concept is conducted in order to evaluate a set of alternative reinforcement system prototypes. Before the reinforcement systems are evaluated, technical literature pertaining to alternative reinforcements is reviewed. Select specimens provided evidence of sufficient mechanically constrictive behavior. Indications of good bond strength and shear strength contribution from the flexural reinforcement systems were also found. Parameters which control the structural behavior of the reinforcement system were identified.
Open Access
Evaluation of rapid scanning techniques for inspecting concrete bridge decks with asphalt overlay
(Colorado State University. Libraries, 2016) Vemuri, Sri Harsha, author; Atadero, Rebecca, advisor; Chen, Suren, committee member; Strong, Kelly, committee member
The average age of bridges in the USA is 42 years. The life expectancy of a majority of these bridges is 50 years. At the current rates of aging and replacement, almost half of the nation’s bridges will require major structural investment in the next 15 years as stated by the Federal Highway Administration. There is a severe deficiency in both time and resources available to address this problem, and methods to increase efficiency are needed. Bridge decks are the most critical elements of a bridge structure as they are directly and continuously exposed to harsh weather conditions and cyclic loading from traffic throughout their lifespan. This thesis attempts to improve management practices for bridge decks by addressing current challenges faced by the Colorado Department of Transportation (CDOT) in estimating the extent of damage on bridge decks. The current bridge deck inspection method being employed by CDOT is sounding and chipping. This procedure involves sounding the deck with chains, hammers and rotary percussion to detect the deteriorated areas followed by chipping. The issues with this procedure include its time-consuming nature, the requirement for traffic to be diverted for extended periods and the costs associated with the inspection and traffic diversion. Additionally, sounding is not adequate to provide a rough estimation of the class of damaged area and the resulting expenses. CDOT wants to take the advantage of newer alternative techniques to evaluate bridge decks. The alternative evaluation considered by CDOT involves using Ground Penetrating Radar (GPR) and Infrared Thermography (IR) thermography together for evaluating bridge decks. The major advantage of using GPR is that it is the only available method that can estimate the deterioration in concrete decks with asphalt overlay. Additionally, GPR can estimate the deterioration in early stages, unlike sounding which detects damage in advanced stages and GPR is also capable of detecting corrosion in rebars. Thus, GPR not only has the potential to address the disadvantages of sounding it also has additional advantages which can benefit the life of the bridge deck. This study attempts to understand the limitations that this newer evaluation method comes with and possibly solve some of these limitations to take complete advantage of this technology. This study took advantage of the available as-built data of four bridge decks rebuilt after sounding and chipping and the data available from GPR and IR scanning of the respective decks to study the limitations from using GPR and IR technologies. The scanned results from GPR and IR thermography are compared to the deck condition data from sounding and chipping. In two cases the damage detected by GPR and IR thermography did not correlate well with the damage detected from sounding and chipping. The two decks with reasonable correlation are compared to the decks with poor correlation in an effort to understand the possible causes for deviation in results. It was observed that for the decks with poor correlation the GPR showed areas with higher cover as deteriorated in the estimation. An improved data processing procedure to solve such miss-interpretation issue is suggested, and a coring strategy to assist future research in the direction of eliminating the depth-amplitude effects in GPR scans.
Embargo
Improving soil property predictions for applications in tailings and terramechanics
(Colorado State University. Libraries, 2024) Bindner, Joseph R., author; Scalia, Joseph, advisor; Atadero, Rebecca, advisor; Bareither, Christopher, committee member; Niemann, Jeffrey, committee member; Ham, Jay, committee member
Soil properties are used by engineers and scientists to better understand the state and behavior of soils. For example, soil properties can be used to estimate surficial soil strength for vehicle mobility models and can be used to better understand the engineering characteristics of mine waste (tailings) stored in tailings storage facilities. Soil and tailings properties often have high spatial variability and often require high resolution data for engineering analyses. Standard laboratory procedures are commonly used to determine soil properties but are often impractical for large spatial extents. While some existing soil data products provide estimates of surficial soil properties, the fidelity of soil data products is often poorly understood and insufficient for many applications. Additionally, some field tests used to estimate soil properties, such as the cone penetration test (CPT), rely on empirical correlations that cannot be used for some soils. There remains a need for procedures which improve the speed and accuracy of soil property estimates across large spatial extents. The objectives of this study are to (i) evaluate how surficial soil moisture and soil strength vary with soil and landscape attributes across a large spatial extent, (ii) explore the use of field-based hyperspectral sensing and machine learning for the prediction of surficial soil properties across a landscape, and (iii) assess the use of laboratory hyperspectral sensing and machine learning for the prediction of tailings properties for potential application in situ via direct push methods. Soil and landscape attributes were determined at sampling locations across a semi-arid foothills region and used to assess how soil moisture and soil strength vary with soil and landscape attributes. Then, hyperspectral data were captured at select sampling locations and used to train and assess the performance of a convolutional neural network (CNN) for the predictions of soil properties. Finally, a diverse tailings-hyperspectral dataset was prepared in the lab and used to train and assess a CNN to provide proof of concepts for prediction of material properties relevant to TSF stability analyses.
Open Access
Investigation of mechanistic deterioration modeling for bridge design and management
(Colorado State University. Libraries, 2017) Nickless, Kyle, author; Atadero, Rebecca, advisor; Jia, Gaofeng, committee member; Shuler, Scott, committee member
The ongoing deterioration of highway bridges in Colorado dictates that an effective method for allocating limited management resources be developed. In order to predict bridge deterioration in advance, mechanistic models which analyze the physical processes causing deterioration are capable of supplementing purely statistical models and addressing limitations associated with bridge inspection data and statistical methods. A review of existing analytical models in the literature was conducted. Due to its prevalence throughout the state of Colorado and frequent need for repair, corrosion-induced cracking of reinforced concrete (RC) decks was selected as the mode of deterioration for further study. A mechanistic model was developed to predict corrosion and concrete cracking as a function of material and environmental inputs. The model was modified to include the effects of epoxy-coated rebar, waterproofing membranes, asphalt overlays, joint deterioration, and deck maintenance. Probabilistic inputs were applied to simulate inherent randomness associated with deterioration. Model results showed that mechanistic models may be able to address limitations of statistical models and provide a more accurate and precise prediction of bridge degradation in advance. Preventative maintenance may provide longer bridge deck service life with fewer total maintenance actions than current methods. However, experimental study of specific deterioration processes and additional data collection are needed to validate model predictions. Maintenance histories of existing bridges are necessary to predicting bridge deterioration and improving bridge design and management in the future.
Open Access
Joint elimination retrofits and thermal loading analysis in plate girder bridge using health monitoring and finite element simulations
(Colorado State University. Libraries, 2016) Rager, Karly, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, advisor; Strong, Kelly, committee member
Degradation of United States' public infrastructure has attracted attention from the public and governing agencies alike. A challenge facing transportation departments is management of leaking and clogged expansion joints in bridge structures, which result in significant deterioration to bridge substructures and superstructures. Some agencies have started eliminating these joints. However, technical understanding of which retrofit methodology to employ based on thermal loading and specific characteristics of the structure is lacking. In this study, this problem is investigated with both numerical modeling and analysis of field measurements. Various sensors were installed on the bridge including thermocouples, strain gauges, and linear differential displacement transducers. Following sensor installation, controlled load testing was conducted and the collected data evaluated against numerical and analytical predictions. The installed sensors will allow for long-term monitoring of the bridge to evaluate the effect of seasonal temperature profiles that are characteristic of Colorado on bridge behavior. In addition to gaining technical understanding of site-specific bridge characteristics that influence joint movement using field-testing, numerical finite element analysis was conducted. Specifically, a 3D finite element model was developed and used in a parametric study to assess the effect of various parameters on the stresses occurring in the bridge. The stresses occur due to 1) variation in thermal loading and thermal gradient, 2) clogging of the joint with different materials including gravel and sand, and 3) employment of various repair techniques in eliminating the expansion joints. The results of the numerical models show that clogged joints induce some localized stress but do not significantly affect the global performance of the superstructure. The results also show that a reduction in moment demand on the superstructure is not apparent until a Full-Moment Splice connection is utilized. This study will help engineers to choose the most appropriate method of designing a retrofit for expansion joint removal.
Open Access
Life cycle cost analysis for joint elimination retrofits and thermal loading on Colorado bridges
(Colorado State University. Libraries, 2017) Harper-Smith Kelly, Aura Lee, author; Mahmoud, Hussam, advisor; Atadero, Rebecca, advisor; Strong, Kelly, committee member
Bridge expansion joints are a particularly troublesome component of bridges and many Departments of Transportation (DOTs) are looking for a solution to deteriorating expansion joints on highway bridges. Bridge expansion joints create a break in the structural continuity of a bridge allowing clogging gravels and corroding chlorides to enter. They are designed to absorb thermal movements of the bridge between two bridge elements. There are three main issues regarding expansion joint: maintenance, knowledge about thermal movements, and costs. In order to prevent deterioration due to expansion joints the joints must be cleaned regularly and replaced promptly after failure. However, most DOTs do not have the personnel, time or resources to maintain expansion joints in their districts which leads to bridge deterioration. Other similar maintenance and component issues have been addressed using a Life Cycle Cost Analysis. For this to be used on expansion joints the three main issues of thermal knowledge, maintenance, and costs must first be addressed. The main goal of this project is to help transportation agencies make better decisions about bridge expansion joints. The specific objectives of this study are to 1) expand understanding of thermal loading effects on bridge expansion joints and 2) conduct a LCCA for joint elimination and retrofits for bridges in Colorado. These objectives were accomplished utilizing data from in field instrumentation and finite element models. The study has been developed jointly between the Colorado Department of Transportation (CDOT) and researchers at Colorado State University Three main tasks were conducted to achieve the objectives: 1) collect and analyze long-term thermal loading data from existing bridges to assess thermal loading impacts on joints; 2) perform a parametric study using a calibrated finite element model to further understanding of joint behavior and retrofit options under thermal loads; 3) perform a LCCA for bridge expansion joint retrofitting including impacts on bridge superstructure. The significance of this work includes the results of the data collection and analysis, the parametric study, and the LCCA findings. The preliminary data on the concrete bridge C-17-AT presented in this thesis only accounts for mid-winter temperatures. However, these limited observations do imply that if CDOT is interested in removing an expansion joint, the bridge superstructure and retrofit option would need to support the movement of the bridge. The parametric study and data analysis of thermal gradients indicate a stark need for further research into thermal gradients experienced by bridges. Finally, the LCCA concluded that a retrofit continuous bridge design would provide the most cost effective design by decreasing joint replacement costs and pier cap corrosion.
Open Access
Methodology for uncertainty-based inspection planning of concrete bridge decks using mechanistic models of crack formation and propagation
(Colorado State University. Libraries, 2015) Sanders, Patrick, author; Atadero, Rebecca, advisor; Ozbek, Mehmet, advisor; Senior, Bolivar, committee member
The bridge inspection program in the United States started in 1971 following the collapse of the Silver Bridge in Ohio. Since then, bridges have generally been inspected every two years. This uniform inspection interval for all bridges is not the most efficient system for conducting inspections because many bridges do not require inspections this frequently, and leads to unnecessary use of inspection resources on bridges that do not require them. Efforts toward changing the bridge inspection program to a risk-based program are being made. Such a program would allow for bridge inspection timing to be based on each particular bridge’s need, and each bridge would then be inspected for the components that present the highest risk to the structure. The research presented herein focuses on using the uncertainty in the current condition of concrete bridge decks to plan inspection timing, and to plan inspection type based on limited resources. A mathematical program called Concrete Deck Cracking Probability Model (CDCPM) is written in MATLAB to model the uncertainty in the occurrence of transverse cracking and delamination in the deck. Through literature review, mechanistic models of the processes that affect cracking are determined and implemented in the program. Using Monte Carlo simulations, the uncertainty in the occurrence of cracking and delamination is analyzed based on the input parameter uncertainty. The effect of different climates and mechanistic models on the prediction of cracking is explored using CDCPM. This model is then applied to a bridge in Larimer County, Colorado to see how the results compare to actual inspection results, and then the model is used to plan a future delamination inspection on the bridge. Another scenario is investigated where CDCPM is used together with uncertainty forecast plots to allocate inspection resources to two bridge decks. CDCPM revealed that the uncertainty in the current bridge condition is heavily influenced by the mechanistic models chosen for the analysis, as well as some of the parameters used in the models. The surface chloride content has a large effect on the delamination of the concrete deck, while the relative humidity and ambient temperature for a given location can affect the probability of transverse cracking. Analysis of the Larimer County bridge inspection reports showed that the model can be good indicator of future damage to the deck. The model provides unique insight into inspection planning using uncertainty. Using the model output along with uncertainty forecast plots of different inspection methods, the inspection manager is provided with a useful planning tool that gives information on the effect of inspection methods on bridge condition assessment. Suggestions for implementing the bridge inspection plan for agency use is also provided.
Open Access
Multi criteria decision making models for repair and replacement decisions of condition based building maintenance
(Colorado State University. Libraries, 2017) Besiktepe, Deniz, author; Ozbek, Mehmet E., advisor; Atadero, Rebecca, advisor
Building maintenance is a significant part of Facilities Management which is necessary to sustain the expected performance of the built environment. Different issues such as lack of funding and insufficient resources, increase the impact of decisions in the maintenance process. The main purpose of this study is to generate a decision making model for the effective repair and replacement decisions of building maintenance with a condition assessment support framework and Multi Criteria Decision Making. The expected impact of the study is to analyze the benefits of repair and replacement decisions with the proposed model compared to decisions given without model.
Open Access
Predicting fatigue life extension of steel reinforcement in RC beams repaired with externally bonded CFRP
(Colorado State University. Libraries, 2014) Sobieck, Tyler, author; Atadero, Rebecca, advisor; Mahmoud, Hussam, advisor; Radford, Donald, committee member
A majority of the United States' transportation infrastructure is over 50 years old with one in nine bridges being considered structurally deficient. Fatigue damage accumulation in bridge structures, generated by cyclic loading of passing traffic, has led to shorter service lives. Over the past few decades studies have shown carbon fiber reinforced polymer (CFRP) repairs to be an effective means of reducing fatigue damage accumulation in reinforced concrete (RC) girders. Despite the abundant research, the results, specifically the increase in fatigue life, vary widely making it difficult to apply them directly to repair designs. Therefore, design codes and guidelines presently in use are insufficient in providing engineers with the proper information to determine the extended fatigue life of the RC bridges repaired with CFRP. Current design codes state FRP repairs should limit the stress range in the reinforcing bars below the threshold where fatigue cracks can propagate. The problem with this philosophy is it essentially designs an overly conservative system with an infinite fatigue life. The proposed approach follows a performance based design philosophy for which the engineer designs for a specified extension in service life by limiting the crack growth rate in the reinforcement so the critical crack length, for which fracture in the reinforcement would occur, is never reached in the extended life. In this thesis, the results of experimental fatigue testing of control and CFRP repaired RC beams are highlighted and the fatigue crack propagation rate in the steel reinforcement is assessed for different repair schemes. The focus on steel reinforcement crack propagation rates was made because similar studies have found the reinforcement to be the limiting fatigue component in RC bridge girders. The results of the experimental study showed an extended fatigue life and a slowed crack growth rate in specimens repaired with both CFRP systems. The crack growth rates were then used to determine the material constants for the Pairs Law, which describes growth of a stable fatigue crack. These results were then used to propose recommendations for design of FRP repair systems for RC flexural members for a specific fatigue life.
Open Access
Simple made continuous bridges with steel diaphragms: tension and compression transfer mechanisms
(Colorado State University. Libraries, 2015) Johnson, Robert I., author; Atadero, Rebecca, advisor; Chen, Suren, committee member; Clevenger, Caroline, committee member; Heyliger, Paul, committee member; Mahmoud, Hussam, committee member
Simple-made-continuous (SMC) steel bridges are a relatively new innovation in steel bridge design. The SMC concept has been used for quite some time in the construction of precast concrete bridges and based on current statistics, precast concrete bridge construction is outpacing steel bridge construction by a factor of two to one. The SMC concept is a viable solution for steel bridges to recover market share of the bridges constructed in the United States. The majority of SMC bridges currently in use are constructed with concrete diaphragms. This dissertation presents the results of numerical analysis and laboratory testing of an alternative simple-made-continuous connection scheme that uses steel diaphragms in lieu of concrete diaphragms. A bridge using steel diaphragms was constructed by the Colorado Department of Transportation in 2005 and the connections on this bridge serve as a basis for the research presented herein. Preliminary numerical analysis was performed by hand; this analysis discovered potential design flaws in the current bridge connection. Subsequent numerical analysis using Abaqus finite element analysis software provided results which were indecisive in regard to the flaws found in the hand analysis. The finite element analysis however, did provide valuable insight into some of the connection behavior, which was also verified with the physical test. Physical testing was subsequently performed on a full size model of the connection. The physical model consisted of double cantilever composite girders loaded at their ends with 300 kip actuators to simulate negative moments at the center connection. The physical test verified that there were design flaws in the original design. The results of analysis and physical testing provided information necessary to correct the design flaws and data required for the development of a design methodology based on the actual physical behavior of the SMC connection. Also, particular behaviors noted in the finite element analysis were corroborated with the physical test and the design methodology recognizes these behaviors. The research also compares the steel diaphragm SMC connection to concrete diaphragm connection and demonstrates that the steel diaphragm design has several desirable features. The steel diaphragm design provides for a more economical and quicker to construct steel bridge design and requires less total construction time than other SMC schemes. Additionally, since the girder ends are exposed, the girders are able to fully weather and they may be easily inspected.
Open Access
The effects of design decisions on service life and life cycle cost for a concrete slab in a parking garage
(Colorado State University. Libraries, 2017) Badr, Ali, author; Atadero, Rebecca, advisor; Jia, Gaofeng, committee member; Valdes-Vasquez, Rodolfo, committee member
Parking garages are unique structures that are useful and common as part of the transportation infrastructure system in the US. Large percentage of these structures is open which expose them to ambient environment and in some cases deleterious chloride exposures. Corrosion of embedded steel is the main cause for concrete deterioration and chloride exposure is one of the major causes for corrosion. Therefore, designing these structures for durability is essential to extend their service life and reduce their degradation status and future repair costs. Improving the durability of these structures can be a costly process at the construction phase that might leave owners of parking garages reluctant about increasing the upfront costs. Therefore, Life-365 software has been used in this study to investigate the service life and life cycle cost impacts of different design decisions throughout the lifetime on a reinforced concrete slab element in a parking garage. Life Cycle Cost Analysis "LCCA" is a process that weights the trade-offs of different phases cost including initial construction and subsequent maintenance and repair throughout the design life period and can help understand the long-term value of additional upfront costs. In Life-365, service life is the sum of two periods: the initiation period and the propagation period while LCC is the sum of three cost phases :the construction phase, the barrier phase and the repair phase which starts at the end of the service life period and extends the remainder of design life. The design decisions or design variables that are investigated in this study include varying the concrete cover distance to the embedded steel, varying the w/cm ratio, using different supplementary cementitious materials, using different barriers and reinforcement types. The geographic location of the parking garage was chosen as Denver, Colorado. Corrosion is likely to occur in this city where harsh environmental conditions are present, including snow falling into parking garages' decks or using deicing salts to melt accumulated snow on roads which can be carried by tires or underneath automobiles. Results of this study showed that using supplementary cementitious materials are the best design variables to consider in terms of saving money for the concrete slab during its design life, besides increasing the concrete cover distance. In addition, a combination of SCMs with a low w/cm ratio has proven to be very effective in terms of reducing costs especially when it is used with higher concrete cover. This study can help designers and owners of these structures in managing and allocating the resources they have more effectively.
Open Access
Using building information modeling to track and assess the structural condition of bridges
(Colorado State University. Libraries, 2014) McGuire, Brendan Michael, author; Atadero, Rebecca, advisor; Clevenger, Caroline, advisor; Ozbek, Mehmet, committee member; Elliott, Jonathan, committee member
National Bridge Inspection Standards do not require documenting damage location during an inspection but bridge evaluation provisions highlight the importance of it. When determining a safe load carrying capacity of a bridge, damage location information is significant because shear and moment limit states are more critical at different locations and member capacities can vary along the length of a span. Capturing damage location information using current methods can be impractical; however, building information modeling (BIM) provides new opportunities in tracking and utilizing this information. A method and prototype implementation to apply BIM software to the operation and maintenance stages of bridges' service lives is presented. The proposed Bridge information modeling for Inspection and Evaluation Method (BIEM) could allow transportation agencies to more efficiently manage bridge inventories using BIM capabilities while incorporating damage location information. The method, created by the author, uses BIM to document damage type, amount, severity, and location information during a bridge inspection. To leverage this information, inspection results are exported from the BIM model into a spreadsheet where a custom subroutine evaluates the structural performance and performs load ratings on selected bridge superstructure elements. In addition, based on the type, amount, and severity of damage, estimated repair quantities are given and maintenance recommendations are provided. The proposed method was field tested on a case study bridge in Larimer County, Colorado. Official inspection reports and load ratings were obtained and a visual inspection of the bridge utilizing supplemental location-based measurements was performed. The BIEM was implemented and numerical results were compared to the official load ratings. Results suggest that documenting the location of deterioration within a bridge element can affect the guidelines for determining a safe load carrying capacity for a bridge. In addition, the opportunity exists for BIM to play a significant role in bridge management in the future as demonstrated by its proven ability to facilitate the inspection and evaluation processes which could ultimately result in more automated practices. Overall, results from this research motivate future work in the study of deterioration modes and their effect on bridge element capacity and tailoring the principles BIM to the later stages of bridges' service lives.
Open Access
Using expert opinion to quantify accuracy and reliability of nondestructive evaluation on bridges
(Colorado State University. Libraries, 2013) Hesse, Alex, author; Atadero, Rebecca, advisor; Ozbek, Mehmet, advisor; Chen, Suren, committee member; Nobe, Mary, committee member
Bridge inspection is an important phase in the bridge management process. In 2009, a joint American Society of Civil Engineers Structural Engineering Institute (ASCE/SEI) and AASHTO Ad-Hoc group was created to identify the issues to guarantee bridge safety and to study how current bridge practices could be improved for the future. This group recommended: "A more rational, risk-based approach to determining the appropriate inspection intervals for bridges is needed, as opposed to a set twenty-four month cycle for all bridges". The committee also recommended a wider use of NDE methods. The difficulty in increasing the use of these NDE methods is the increased costs and time spent using them. One way to deal with this is to implement risk based planning to determine the appropriate inspection frequency, scope, intensity, and methodology. To do this, though, the accuracy, reliability, bias, and cost of each test must be quantified. This study attempts to quantify these parameters for common bridge NDE methods. This was done by two methods. Firstly, a literature review was performed to determine common NDE methods being used and studied for bridge inspection and statistical data was found for these methods. To complement the literature, a four round Delphi method survey was conducted with experts in the NDE bridge field in order to develop a broader range of data that matches real life practices. All of the data was then analyzed and conclusions were drawn to quantify the accuracy, reliability, bias, and various costs incurred for common bridge NDE methods. Based on these results it can be seen that most commonly used bridge NDE methods tend to be under biased and relatively repeatable. It was shown, however, that while inspectors seem to have a pretty good relative understanding of the variability in different tests, they tend to not have as clear of an understanding of the absolute scale of the variability. Furthermore, the accuracy of commonly used bridge NDE methods tends to be relatively variable with the average test measuring a true response between 80% and 85% of the time. Lastly the costs associated with the NDE methods examined here tended to be highly variable making this measure difficult to evaluate. However, by comparing the rankings of each of the four categories that were examined for each NDE method, it is possible to correlate the cost of a method to the bias, accuracy and reliability. This could lead to a more reliable risk-based approach to bridge inspection in the future.

Browsing by Author "Atadero, Rebecca, advisor"

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