Experimental Testing and Analytical Modeling of Driven Steel Pile Bridge Bents
Type of DegreeMaster's Thesis
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One of the most common bridge types in Alabama is the multi-span bridge with precast girders and intermediate bents consisting of driven steel piles and a reinforced concrete cap. Due to its common use, effective analysis procedures for these types of bridges would result in the most sustainable use of resources. Driven pile bridge bents represent a soil-structure interaction and the bents are highly indeterminate; therefore assumptions made in analysis of these bents regarding certain boundary conditions including level of composite activity and pile-to-cap fixity are very important. ALDOT had recently highlighted issues with the analysis and design of steel pile bents where design pile forces were significantly higher than anticipated especially under cases involving lateral loads. The assumptions made in the analysis of these bents can have a significant impact on the numerical results. The research presented in this thesis sought to determine the appropriate boundary conditions to use in analysis of these bents through a series of lateral load tests on new construction and in-service bridges. Following testing of these bridges, analytical models were developed in SAP 2000 to determine a correlation between the field results and the models, and to simulate bridge behavior that was difficult to measure in the field. It was concluded that the largest bending moments in the piles of the steel pile bents are developed near the top of the pile which is embedded into the cap, indicating the connection between the pile and the cap acts more as a fixed condition than a pinned condition. In cases where the piles were encased in concrete, the overall lateral stiffness of the bent is increased significantly due to the large moment of inertia of the encasements. Furthermore, during tests performed in which an ALDOT load truck was used to apply gravity load, it was found that the live load induced a lateral deflection opposite in direction than the deflections from the tests without the truck. As a result, smaller net deflections were measured in the load tests with the load truck. These results were similar in the analyses performed in the SAP models as well.