<p dir="ltr">Link slabs offer a cost-effective solution for eliminating deck expansion joints in multi-span bridges. A link slab is the cast-in-place concrete portion that makes only the deck slab continuous while the girders remain simply supported between two adjacent deck spans. By closing the expansion-joint opening, link slabs can reduce the costs of repairing and rehabilitating leaking joints and improving the bridge riding surface. Link slabs are designed to resist the bending moments imposed by girder end rotation due to live load plus impact, assuming the bridge spans are simply supported at the joints. The continuity provided by the link slab under live load is neglected, based on the assumption that its stiffness is lower than that of the girders. Furthermore, structural elements capable of load transfer (e.g., stirrups and shear stud connectors) within the limits of the deck joint elimination are often removed to reduce induced stresses in the link slab. A bond breaker is placed between the top of the girders and the bottom of the link slab to mitigate stresses. The debonded length, typically set at 5% of each span length, defines the total length of the link slab. Practices may vary among states, such as Indiana, where a composite action between the link slab and supporting girders is maintained. </p><p dir="ltr">However, increased cracking observed in the field is the primary concern about debonded link slabs. Once the cracks form, they allow the entrance of corrosive chemicals and debris, causing deterioration of concrete bridge components. The causes of the increased cracking and resulting leakage at the link slabs have been associated with the limitations of the existing design approaches in considering the effects of thermal loads and support conditions. This study presents a comprehensive finite element analysis to evaluate the behavior of bridge deck link slabs under the combined effect of traffic loads and vertical temperature gradients. The link slabs are subjected to HL-93 loading and temperature gradients following AASHTO LFRD Bridge Design Specifications. A finite element model of the Plott Creek Bridge in Haywood country in North Carolina, instrumented by Wing & Kowalksy (2005), is developed using ABAQUS/Standard software. The numerical model is validated against test data from previous studies available in the literature.</p><p dir="ltr">The results of the numerical investigation reveal that vehicular traffic loading is the primary factor contributing to the cracking of the link slabs. However, vertical temperature gradients are also identified as significant factors inducing stresses within the link slabs. Specifically, the combination of live load and a negative temperature gradient is the most influential loading condition contributing to cracking at the top surface of the link slabs. It is important to note that the rotation of the girder ends due to live load induces a negative moment (tension at the top) on the link slab. A negative temperature gradient, where the temperature on the top deck surface is lower than that on the web of the beams, results in an additional negative moment on the link slab due to its addition to the rotation from the live load. The temperature gradients are observed to increase the girder end rotation obtained from live load analysis for simply supported beams by approximately 20% in the range of parameters considered in the present study. This finding underscores the importance of considering temperature effects in link slab design to ensure structural integrity. </p><p dir="ltr">Furthermore, parametric studies are conducted to assess the impact of various factors such as girder support conditions, span length, debonded zone length, and material properties on crack initiation in link slabs. The analyses show that the primary factors affecting the tensile stress developed in the link slabs are the span length and the girder support conditions. This highlights the importance of considering these factors when designing link slabs. Based on the findings, design recommendations are proposed to enhance the current practices for link slab design. These recommendations include considering temperature gradients alongside live loads, adopting distributed bar spacing for crack control, and incorporating an allowable stress limit of 0.60fy for steel reinforcement following AASHTO LFRD Bridge Design Specifications. Given that link slabs exhibit cracking under service conditions, it is advisable to determine the amount of longitudinal tension reinforcement based on cracked section analysis rather than simply providing the minimum reinforcement. Furthermore, incorporating a debonded zone within 5% to 7.5% of the span length at each side of the link slab is recommended to reduce stresses. The use of roller support is not recommended for link slab applications, while hinge supports can be effective if the span length is less than 15~m (50~ft.). </p>

Highway bridges are among the most vulnerable and expensive components in transportation networks. In response, the Government of Ontario has allocated $26 billion in the next 10 years to address issues pertaining to aging bridge and deteriorating highway infrastructure in the province. Although several approaches have been developed to guide their rehabilitation, most bridge rehabilitation approaches are focused on the component level (individual bridge) in a relative isolation of other bridges in the network. The current study utilizes a complex network theoretic approach to quantify the topological characteristics of the Ontario Bridge Network (OBN) and subsequently evaluate the OBN robustness and vulnerability characteristics. These measures are then integrated in the development of a Multi Scale Bridge Classification (MSBC) approach—an innovative classification approach that links the OBN component level data (i.e., Bridge Condition Index and year of construction, etc.) to the corresponding dynamic network-level measures. The novel approach calls for a paradigm shift in the strategy governing classifying and prioritizing bridge rehabilitation projects based on bridge criticality within the entire network, rather than only the individual bridge’s structural conditions. The model was also used to identify the most critical bridges in the OBN under different disruptions to facilitate rapid implementation of the study results. / Thesis / Master of Applied Science (MASc)

The deterioration of highway bridges and structures and the cost of repairing, rehabilitating, or replacing deteriorated structures is a major issue for bridge owners. An aging infrastructure as well as the need to upgrade structural capacity for heavier trucks adds to problem. Life-cycle cost analysis (LCCA) is a useful tool for determining when the deployment of fiber-reinforced polymer (FRP) composite components is an economically viable alternative for rehabilitating deteriorated concrete bridges. The use of LCCA in bridge design and rehabilitation has been limited. The use of LCCA for bridges on a project level basis has often been limited to the non-routine design of major bridges where the life-cycle cost model is customized. LCCA has historically been deterministic. The deterministic analysis uses discrete values for inputs and is fairly simple and easy to do. It does not give any indication of risk, i.e. the probability that the input values used in the analysis and the resulting life-cycle cost will actually occur. Probabilistic analysis accounts for uncertainty and variability in input variables. It requires more effort than a deterministic analysis because probability distribution functions are required, random sampling is used, and a large number of iterations of the life-cycle cost calculations are carried out. The data needed is often not available. The significance of this study lies in its identification of the parameters that had the most influence on life-cycle costs of concrete bridge and how those parameters interacted. The parameters are: (1) Time to construct the new bridge; (2) traffic volume under bridge (when applicable); (3) value of time for cars; and (4) delay time under the bridge during new bridge construction (when applicable). Using these parameters the analyst can now “simulate” a probabilistic analysis by using the deterministic approach and reducing the number of iterations. This study also extended the use of LCCA to bridge rehabilitations and to bridges with low traffic volumes. A large number of bridges in the United States have low traffic volumes. For the highway bridge considered in the parametric study, rehabilitation using FRP had a lower life-cycle cost when compared to the new bridge alternative.

Fiber reinforced polymeric (FRP) composite materials are beginning to find use in construction and infrastructure applications. Composite members may potentially provide more durable replacements for steel and concrete in primary and secondary bridge structures, but the experience with composites in these applications is minimal. Recently, however, a number of groups in the United States have constructed short-span traffic bridges utilizing FRP members. These demonstration cases will facilitate the development of design guidelines and durability data for FRP materials. The Tom's Creek Bridge rehabilitation is one such project that utilizes a hybrid FRP composite beam in an actual field application. This thesis details much of the experimental work conducted in conjunction with the Tom's Creek Bridge rehabilitation. All of the composite beams used in the rehabilitation were first proof tested in four-point bending. A mock-up of the bridge was then constructed in the laboratory using the actual FRP beams and timber decking. The mock-up was tested in several static loading schemes to evaluate the bridge response under HS20 loading. The lab testing indicated a deflection criterion of nearly L/200; the actual field structure was stiffer at L/450. This was attributed to the difference in boundary conditions for the girders and timber panels. Finally, the bridge response was verified with an analytical model that treats the bridge structure as a wood beam resting upon discrete elastic springs. The model permits both bending and torsional stiffness in the composite beams, as well as shear deformation. A parametric study was conducted utilizing this model and a mechanics of laminated beam theory to provide recommendations for alternate bridge designs and modified composite beam designs. / Master of Science

<p dir="ltr">Girder ends of steel bridges can be corrosion damaged due to deicing salts, water, and other contaminants leaking from deck expansion joints. When the corrosion becomes significant, it can decrease the sectional properties of end steel girders and eventually reduce structural resistance against bearing and shear. Conventional methods that are typically used to repair corrosion-damaged girders require a substantial amount of time and resources to complete and often cause public inconvenience due to traffic lane closure. Therefore, there is a need for practical, rapid, and robust repair methods that can be implemented by maintenance personnel of a local Department of Transportation (DOT).</p><p dir="ltr">In this study, five innovative repair methods for corroded steel girders were evaluated through a selection process called the House of Quality Matrix, a commonly used tool in the consumer product industry. After completing the evaluation and additional numerical simulations, the "Sandwich Panel" repair method was selected for further investigation. The main concept of the proposed "Sandwich Panel" repair method is the encasement of the corroded region with a filler material reinforced by threaded rods. Two thin steel plates installed on both girder sides serve as stay-in-place formwork, expediting the installation process. This repair method eliminates labor-intensive steps of jacking, welding, and formwork disassembly, making it more cost-effective and less time-consuming.</p><p dir="ltr">The structural performance of the method was evaluated experimentally by conducting seven large-scale tests. Various test parameters were considered in the tests, including i) threaded rod layout, ii) filler material, and iii) support condition. The test specimens were corrosion-damaged steel girders from decommissioned highway bridges in Indiana. The experimental results indicate that the method is effective enough to recover the girder's original design strength. The experimental evaluation was followed by a numerical parametric study using finite element models benchmarked using the experimental results. Detailed design guidelines and recommendations were developed based on the experimental and numerical results.</p>

The Tom's Creek Bridge is a small-scale demonstration project involving the use of fiber-reinforced polymer (FRP) composite girders as the main load carrying members. The project is intended to serve two purposes. First, by calculating bridge design parameters such as the dynamic load allowance, transverse wheel load distribution and deflections under service loading, the Tom's Creek Bridge will aid in modifying current AASHTO bridge design standards for use with FRP composite materials. Second, by evaluating the FRP girders after being exposed to service conditions, the project will begin to answer questions about the long-term performance of these advanced composite material beams when used in bridge design. This thesis details the In-Service analysis of the Tom's Creek Bridge. Five load tests, at six month intervals, were conducted on the bridge. Using mid-span strain and deflection data gathered from the FRP composite girders during these tests the above mentioned bridge design parameters have been determined. The Tom's Creek Bridge was determined to have a dynamic load allowance, IM, of 0.90, a transverse wheel load distribution factor, g, of 0.101 and a maximum deflection of L/488. Two bridge girders were removed from the Tom's Creek Bridge after fifteen months of service loading. These FRP composite girders were tested at the Structures and Materials Research Laboratory at Virginia Tech for stiffness and ultimate strength and compared to pre-service values for the same beams. This analysis indicates that after fifteen months of service, the FRP composite girders have not lost a significant amount of either stiffness or ultimate strength. / Master of Science

Adjacent precast, prestressed box beam bridges have a history of poor performance and have been observed to exhibit common types of deterioration including longitudinal cracking, concrete spalling, and deterioration of the concrete top flange. The nature of these types of deterioration leads to uncertainty of the extent and effect of deterioration on structural behavior. Due to limitations in previous research and understanding of the strength of deteriorated box beam bridges, conservative assumptions are being made for the assessment and load rating of these bridges. Furthermore, the design of new box beam bridges, which can offer an efficient and economical solution, is often discouraged due to poor past performance. Therefore, the objective of this research is to develop improved recommendations for the inspection, load rating, and design of adjacent box beam bridges. Through a series of bridge inspections, deteriorated box beams were identified and acquired for experimental testing. The extent of corrosion was determined through visual inspection, non-destructive evaluation, and destructive evaluation. Non-destructive tests (NDT) included the use of connectionless electrical pulse response analysis (CEPRA), ground penetrating radar (GPR), and half-cell potentials. The deteriorated capacity was determined through structural testing, and an analysis procedure was developed to estimate deteriorated behavior. A rehabilitation procedure was also developed to restore load transfer of adjacent beams in cases where shear key failures are suspected. Based on the understanding of deterioration developed through study of deteriorated adjacent box beam bridges, improved inspection and load rating procedure are provided along with design recommendations for the next generation of box beam bridges.