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Simplifying Cast-in-Place Joint Design Using ABC Pocket Connection Details in High Seismic Regions
AuthorSchwartz, Taylor Justine
Civil and Environmental Engineering
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Accelerated bridge construction (ABC) utilizes precast members to minimize on-site construction time, making it an appealing alternative to conventional cast-in-place (CIP) construction. The connections between these precast members are crucial as they must maintain structural integrity, and in regions of moderate and high seismic activity, ensure the ductile behavior of bridge columns. Recent research has demonstrated that pocket (socket) connections meet these requirements while simplifying the construction of joints. Pocket connections allow precast members to be inserted into adjacent members. To form a pocket connection between a column and cap beam, the longitudinal reinforcement in the cap beam must be bundled outside the pocket to allow the precast column to extend into the pocket uninhibited. Earthquake-resistant CIP column-cap beam joints are difficult to construct because the column reinforcement must be threaded through the reinforcement of the cap beam. Additional reinforcement is also necessary within the joint, which can lead to rebar congestion. The primary goal of this study was to adapt ABC pocket connection details for use in CIP column-cap beam joint construction to avoid steel congestion and simplify construction. To achieve this goal, a CIP emulating ABC pocket connection detail was developed, implemented in a large-scale test model, and evaluated under seismic loading on a shake table. Summary design recommendations for the connection based on the results of the shake table testing were then developed. This project consisted of an experimental study, analytical studies, and development of detailing recommendations. The experimental study involved shake table testing of a 1/3 scale CIP model of a column and cap beam which incorporated a novel CIP pocket connection. The specimen was subjected to multiple runs of simulated, scaled versions of the 1994 Northridge earthquake event recorded at the Sylmar Converter Station. Results from the experimental study showed the column reached a drift ratio of 7.8 percent, and the connection was effective in forming the plastic hinge in the column while keeping the joint and cap beam free of damage. The cap beam behaved as a capacity-protected member, and met the seismic performance objective of both CIP and ABC bridges. Analytical models were developed before testing to estimate the response of the specimen. After testing, the models were refined, and calculated results were compared with the measured results. These studies revealed that relatively simple analytical models could estimate the global response of the specimen under dynamic loading with reasonable accuracy. Finally, design recommendations for CIP pocket column-cap beam connections emulating ABC were developed based on the performance of joint reinforcement during the testing.