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Development and Seismic Evaluation of Pier Systems w/Pocket Connections, CFRP Tendons, and ECC/UHPC Columns
Civil and Environmental Engineering
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Deployment of accelerated bridge construction (ABC) technology has been gaining momentum in recent years. ABC offers many advantages over conventional bridge construction by expediting onsite construction while shortening traffic delays and road closures, thus better serving the traveling public. The use of prefabricated reinforced concrete members is essential in ABC because these members can be fabricated concurrently while field preparation is in progress. ABC provides the opportunity for advanced and low-damage materials to be incorporated in the design of the prefabricated bridge components under controlled environmental conditions to provide superior bridge seismic performance and improve resiliency. ABC has been widely used in low seismic regions mostly in superstructures. The application of ABC in high seismic zones has been limited due to insufficient research results and guidelines for seismic design of prefabricated members and connections. The primary aim of this study was to help address this gap.The main objectives of this study were to evaluate seismic performance of precast bridge columns with pocket connections and develop seismic design methods to facilitate the use of ABC in practice. Another objective of the study was to incorporate advanced materials, such as carbon fiber reinforced polymer (CFRP) tendon, ultra-high performance concrete (UHPC), and engineered cementitious composite (ECC), in design of bridge columns to improve the seismic performance and post-earthquake serviceability of precast bridges. This study consisted of three parts, experimental studies, analytical studies, and design method development. The experimental studies involved shake table testing of a 0.33-scale model of a square column and a two-column bent. For the first time, unbonded CFRP tendons and UHPC were incorporated in design of a precast square column. Unbonded CFRP tendons were used to post-tension the column, and UHPC was used in the plastic hinge zone of the column and conventional concrete elsewhere. The column model was connected to a precast footing with a square pocket (also known as socket) connection. Successive motions simulating scaled versions of the 1994 Northridge-Rinaldi earthquake were used in the shake table tests. Results showed that the drift ratio and displacement ductility capacity of the column were 6.9% and 13.8, respectively, and the residual displacement was negligible. The column-footing pocket connection was effective in forming the plastic hinge in the column with no connection damage. The objectives of studying the two-column bent model were to evaluate the seismic response of cap-beam column pocket connections and the relative merit of UHPC and ECC in reducing damage in column plastic hinges. The columns were connected to a precast footing and a precast cap beam using pocket connections. The bent was subjected to successive motions simulating scaled versions of the 1994 Northridge-Sylmar earthquake until failure. Results showed that pocket connections performed well and the structural integrity was maintained up to drift ratio of 9.6% and displacement ductility of 12. UHPC and ECC effectively reduced the column plastic hinge damage, although the extent and location of damage for the two materials were different at failure.The analytical models presented in this study for both single column model and two-column bent model were found to be relatively simple and sufficiently accurate to capture the global seismic response of the models. To facilitate the use of ABC in practice, preliminary seismic design methods were developed based on the experimental results and the analytical investigations of this project and previous studies and were integrated with the AASHTO provisions. The design methods were practical as demonstrated in three design examples.