Repair and Testing of Out-of-Plane Seismic Response of Pocket Connections

US Transportation Collection2020PDFTech ReportRomero, Allan J.Moustafa, Mohamed A.Saiidi, M. SaiidEbrahimian, HamedUniversity of Nevada, RenoNevada. Department of TransportationNevada. Dept. of TransportationUnited StatesAccelerated bridge constructionCast in place concreteRepairingShaking table testsCast-in-place (CIP) construction023-20-803023-20-803Final Report March 2020 to January 2022Accelerated bridge construction (ABC) has been utilized in precast bridge structures because of its advantage to expedite on-site construction. In ABC, one of the main concerns is the joint connection as it needs to be well designed to maintain structural integrity. Several studies were able to demonstrate the effectiveness of ABC pocket connections for partial and fully precast columns. The pocket connections are designed to have the cap beam longitudinal reinforcements bundled outside the joint allowing the placement of the column uninhibited. On the contrary, this has been an issue for cast-in-place (CIP) construction where congestion of the reinforcements in the joint regions is typical. A recent study at the University of Nevada, Reno (UNR) was conducted by utilizing ABC pocket connection in CIP bridges. The specimen was tested at UNR Earthquake Engineering Laboratory on a shake table in an upside-down configuration using an increasing scaled ground motion. The specimen performed well under out-of-plane ground motion excitations and the ductility of the column was confirmed through typical plastic hinge behavior. In this study, the main objective is to further use the specimen from the recent UNR test to repair the damaged column and to test the repaired specimen using the same loading protocol as the original model. The objective was achieved by developing a repair method using flush cutting and coring of the damaged column. A new column was constructed using the exact reinforcements as the original model. However, the column was cast monolithically in the pocket joint as opposed to the original model where the column reinforcement sat in two different concrete casts with a cold joint at the column-cap beam interface. The repaired column was subjected to the same loading protocol as the original model using the scaled 1994 Northridge earthquake ground motion recorded at the Sylmar Converter Station. The repaired specimen performed well as the plastic hinge zone developed in the column outside the joint, close to the interface of the cap beam, as desired and required by design. The results were compared to the original specimen and the maximum drift ratio for 20% through 450% of the earthquake motion was relatively equal. However, for 550% and 650% of the earthquake motions, the drift ratio in the repaired specimen was significantly larger compared to the original specimen. The high drift ratios were attributed to the slippage of the column in the joint and were validated by an increase in the ratios between the rotations of the original and repaired column recorded at the base. The cap beam remained essentially elastic, i.e. capacity-protected as required, throughout the test which is similar to the performance of the original model. Lastly, recommendations for the repair of CIP cap beam-column emulating ABC pocket connection are provided with special attention to roughen the pocket joint connection to develop a sufficient bond between the two members.137