Thesis (M. Sc. Eng.), University of Hong Kong. / Erratum slip inserted. Mimeographed.

Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf 113).

Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaf [57]).

Thesis--Auburn University, 2009. / Abstract. Includes bibliographical references (p. 142-143).

The durability of infrastructure components, such as prestressed concrete bridge beams, can be significantly affected by long-term deterioration associated with corrosion. Corrosion is a major concern for bridges in Virginia, due to the frequent use of deicing salts during the winter, as well as the number of structures in marine environments. The residual capacity of corrosion damaged prestressed I-beams and box beams needs to be accurately estimated to determine if damaged bridges need to be posted, and to help with making informed decisions related to repair, rehabilitation and replacement of damaged bridges. The initial stage of the research investigated the ability to determine the in-situ strength of members that have visible corrosion-related damage. In this stage, six corrosion-damaged beams were investigated. Prior to testing, the beams were visually inspected and damage was documented. The beams were then tested in the lab to determine their flexural strength. Following testing, samples of strands were removed and tested to determine their tensile properties while cores were taken to determine compressive strength. Powdered concrete samples were removed to perform chloride concentration tests. The tested strengths of the beams were compared to calculated strengths using two methods for damage estimation and two different calculation approaches. Two repair methods were then evaluated through large-scale experimental testing, aimed at restoring the strength of deteriorated prestressed concrete beams. The investigated repairs included External Post-Tensioning (PT) and Carbon Fiber Reinforced Polymer (CFRP) laminates applied to the bottom flange of beams for flexural strengthening. A total of five full-scale bridge members were tested to failure throughout this stage. All beams were subjected to monotonically increasing loads until failure. For beams repaired with external PT, the experimental test was accompanied by a detailed approach for determining the ultimate failure load, the ultimate stress in the external tendons, and the location of the failure. For beams repaired with CFRP, the experimental test was accompanied by a parametric study that was performed to determine the maximum reduction in flexural strength for which CFRP can be considered as a viable repair method to restore the lost capacity. This dissertation provides additional information on estimating the residual capacity of corrosion-damaged beams and shows the types of repair that can restore their original strength. With this information, Departments of Transportation (DOT) can properly determine what types of repair are a suitable for the damaged girders based on their level of corrosion. / Doctor of Philosophy / Many bridges in the United States were built using longitudinal members, called girders, made of prestressed concrete. In prestressed concrete, because concrete cannot resist high tensile forces, tensioned steel cables, called strands, are used to produce compression on the concrete member to improve its behavior when it is in service. Corrosion induces cracks in the concrete superstructure which accelerates the deterioration rate and can result in a partial loss of the concrete body and exposure of the embedded steel. This causes degradation in the load-carrying capacity of the bridge girders which raises a danger to vehicles, passengers, and pedestrians. The residual capacity of corrosion damaged prestressed I-beams and box beams needs to be accurately estimated to determine if damaged bridges need to be posted, and to help with making informed decisions related to repair, rehabilitation and replacement of damaged bridges. The initial stage of the research investigated the ability to determine the in-situ strength of members that have visible corrosion-related damage. In this stage, six corrosion-damaged beams were investigated. Prior to testing, the beams were visually inspected, and damage was documented. The beams were then tested in the lab. Following testing, samples of strands were removed and tested to determine their tensile properties while cores were taken to determine compressive strength. Powdered concrete samples were removed to perform chloride concentration tests. The tested strengths of the beams were compared to calculated strengths. Two repair methods were then evaluated through large-scale experimental testing, aimed at restoring the strength of deteriorated prestressed concrete beams. The investigated repairs included External Post-Tensioning (PT) and Carbon Fiber Reinforced Polymer (CFRP) sheets applied to the bottom of beams for flexural strengthening. A total of five full-scale bridge members were tested to failure throughout this stage. All beams were subjected to monotonically increasing loads until failure. For beams repaired with external PT, the experimental test was accompanied by a detailed approach for determining the ultimate failure load, the ultimate stress in the external tendons, and the location of the failure. For beams repaired with CFRP, the experimental test was accompanied by a parametric study that was performed to determine the maximum reduction in flexural strength for which CFRP can be considered as a viable repair method to restore the lost capacity. This dissertation provides additional information on estimating the residual capacity of corrosion-damaged beams and shows the types of repair that can restore their original strength. With this information, Departments of Transportation (DOT) can properly determine what types of repair are a suitable for the damaged girders based on their level of corrosion.

Corrosion is a concern in old prestressed concrete bridges, especially bridges built in marine environments. Corrosion induces cracks in the concrete superstructure which accelerates the deterioration rate and can result in a complete loss of the concrete cover and exposure of the reinforcing and prestressing steel. This causes degradation in the load-carrying capacity of the bridge girders. Consequently, decisions need to be made on whether to replace, retrofit, or load post these bridges. Extensive research has focused on the flexural strength of corroded prestressed concrete girders. This research studies the shear strength of corroded prestressed concrete girders which can, then, be expanded further to evaluate the possible retrofitting techniques for restoring, or enhancing, their shear strengths. Two old prestressed concrete girders built in the 1960's and 1970's were delivered to the Murray Structural Engineering Laboratory at Virginia Tech from two decommissioned bridges in Virginia. The two girders showed signs of deterioration due to corrosion. Non-destructive testing was performed to evaluate their in-situ conditions. For both girders, each end was tested in the lab in three-point loading condition to make full use of the girders. Shear capacities of the girders were predicted using four methods in the current AASHTO LRFD and the ACI codes. In addition, analysis using Response2000 and strut-and-tie modelling were also carried out. Evaluation of these methods and comparisons with the experimental results were performed to reach to conclusions and recommendations for future work. Corrosion in strands seemed to not have as much influence on the shear capacity as on the flexural capacity. Destructive shear tests indicated that the actual shear capacities of the girders investigated in this research exceeded nominal capacities predicted by the current codes. However, the flexural capacities were reduced. Possible reasons for the girders' behaviors are discussed. / Master of Science / Many bridges in the United States were built using longitudinal members, called girders, made of prestressed concrete. In prestressed concrete, because concrete cannot resist high tensile forces, tensioned steel cables, called strands, are used to produce compression on the concrete member to improve its behavior when it is in service. Corrosion is a concern in old prestressed concrete bridges, especially bridges built in marine environments. Corrosion induces cracks in the concrete superstructure which accelerates the deterioration rate and can result in a partial loss of the concrete body and exposure of the embedded steel. This causes degradation in the load-carrying capacity of the bridge girders which raises a danger to vehicles, passengers, and pedestrians. Consequently, decisions need to be made by authorities on whether to replace, repair, or load post these bridges. Two main types of loads exist in bridge girders, namely shear forces and bending moments. Extensive research has focused on the ability of corroded prestressed concrete girders to resist stresses produced by moment, or flexure. However, bridge girders must also resist shear forces. This research studies the shear strength of corroded prestressed concrete girders which can, then, be expanded further to evaluate the possible retrofitting techniques for restoring, or enhancing, their shear strengths. Two old prestressed concrete girders built in the 1960's and 1970's were delivered to the Murray Structural Engineering Laboratory at Virginia Tech from two decommissioned bridges in Virginia. The two girders showed signs of deterioration due to corrosion. These signs include concrete losses, cracks, areas of unsound concrete, and exposed strands. Non-destructive testing was performed on the girders to evaluate the severity of their in-situ conditions. Then, two destructive full-scale tests were performed on each girder in the lab to estimate their actual shear strengths. Shear strengths of the girders were also predicted using four methods present in the current American Association of State Highway and Transportation Officials, AASHTO, and the American Concrete Institute, ACI, codes. In addition, analyses using other advanced tools were also carried out. Evaluation of these methods and comparisons with the experimental results were performed to reach to conclusions and recommendations for future work. Corrosion in strands seemed to not have as much influence on the shear strength as on the flexural strength. Destructive shear tests indicated that the actual shear strengths of the girders investigated in this research exceeded nominal strengths predicted by the current codes, the AASHTO and the ACI. However, the flexural strengths were reduced. Possible reasons for the girders' behaviors are discussed.

The Hampton Roads Bridge-Tunnel is one of the oldest prestressed concrete structures in the United States. The 3.5 mile long twin structure includes the world's first underwater tunnel between two man-made islands. Throughout its 60 years in service, the harsh environment along the Virginia coast has taken its toll on the main load carrying girders. Concrete spalling has exposed prestressing strands within the girders allowing corrosion to spread. Some of the more damaged girders have prestressing strands that have completely severed due to the extensive corrosion. The deterioration has caused select girders to fail the necessary load ratings. The structure acts as an evacuation route for the coast and is a main link for the local Norfolk Naval Base and surrounding industry. Because of these constraints, load posting is not a viable option. Live load testing of five spans was performed to investigate the behavior of the damaged spans. Innovative techniques were used during the load test including a wireless system to measure strains. Two different deflection systems were implemented on the spans, which were located about one mile offshore. The deflection data was later compared head to head. From the load test results, live load distribution factors were developed for both damaged and undamaged girders. The data was also used by the local Department of Transportation to validate computer models in an effort to help pass the load rating. Overall, this research was at the forefront of the residual strength of prestressed concrete girders and the testing of in-service bridges. / Master of Science

<div> <p>Due to harsh environmental conditions, the deterioration of prestressed concrete bridge girders is a commonly observed phenomenon in Indiana and much of the Midwest. Concordantly, one widely observed damage scenario is deteriorated end regions of prestressed concrete girders. Damaged or failed expansion joints expose prestressed concrete girder end regions to chloride-laden water, resulting in a corrosive environment in which reinforcement section loss and concrete spalling can occur. For bridges experiencing this type of deterioration, action is needed to ensure the structure remains safe and serviceable. As such, an experimental program was developed to investigate the effectiveness of three repair techniques in restoring the structural behavior of prestressed concrete bridge girders with end region deterioration. The three examined repair techniques are (i) an externally bonded fiber reinforced polymer (FRP) system, (ii) a near-surface-mounted (NSM) FRP system, and (iii) a concrete supplemental diaphragm. Additionally, installation procedures for the three end region repair techniques were developed. Results, conclusions, and recommendations from the experimental program are presented to help advise best practices for implementing end region repair techniques in the field. </p> </div> <br>