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.