United States Department of Transportation
i
Development and Seismic Evaluation of Cast-in-Place Emulating ABC Pocket Connections and SMA Reinforced Two-Way Hinges
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2021-06-01
[PDF-37.36 MB]
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Alternative Title:Column and Footing Pocket Connections for Cast-in-Place and Precast Construction [Cover title]
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Edition:Final report
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Abstract:Accelerated bridge construction (ABC) may be preferable to conventional cast-in-place (CIP) construction because it can significantly expedite project delivery. The design of precast member connections is critical as the connections must maintain structural integrity and provide for ductile behavior under strong earthquakes. Pocket/socket connections are a type of ABC connection that eliminates the need to thread bars through the column cage which can be time consuming and cause rebar congestion. The primary goal of this study was to evaluate the performance and viability of a CIP column-cap joint that was detailed similar to ABC pocket/socket connections to reduce steel congestion. Another objective of the study was to explore the use of superelastic Copper-Aluminum-Manganese (CAM) shape memory alloy (SMA) bars at two-column base hinges. Superelastic SMA bars are known to have reduced permanent deformation of concrete bridges under seismic loads. To achieve the primary goal of the study, a CIP emulating ABC pocket connection design was developed and implemented in a 0.33-scale test model. The test model was a two-column bent, wherein one of the column-cap connections utilized the novel CIP pocket connection and the other utilized a traditional ABC pocket connection. Both connections were designed identically according to existing guidelines for ABC pocket connections. Auxiliary transverse cap beam reinforcement was placed around the connections to reduce joints stresses and address prying forces. The secondary objective of the study was achieved by implementing two-way hinges reinforced with CAM bars at the base of both columns. The test specimen was instrumented with strain gauges, displacement transducers, accelerometers, and cameras to measure local and global responses. The experimental study involved shake table testing of the test bent subjected to multiple runs of simulated, scaled versions of the 1940 Imperial Valley El Centro record. The bent reached a drift ratio of 11.2 percent, yet the connections were effective in forming the plastic hinge in the columns while the joints remained damage-free. Capacity-protected behavior was also observed in the cap beam for both connections as the cap beam reinforcement around the connection remained elastic. The CAM reinforced two-way hinges maintained the integrity of the column bases with substantial yielding and energy dissipation. Post-test analytical studies of the bent were conducted by using actual material properties and shake table motions. Comparison of the calculated and measured results showed that a relatively routine OpenSees model can be used to obtain an approximate response for moderate and strong earthquakes of up to approximately twice the design earthquake. Finally, the design of CIP pocket connections emulating ABC was evaluated in light of the measured seismic performance of the bent.
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