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CCEER-20-08: Seismic Response Of Precast Columns With Non-Proprietary UHPC-Filled Ducts Abc Connections
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Accelerated bridge construction (ABC) has several advantages, such as reducing onsite construction time, reducing the traffic congestion around construction sites, and improving the quality of the prefabricated elements for both new bridges or rehabilitation or replacement of old bridges. ABC is considered a good and efficient candidate to replace the cast-in-place (CIP) conventional on-site construction techniques. ABC has been widely used in low seismic regions mostly in the superstructure elements. However, ABC is not widely implemented in the substructure elements such as column-base connections, especially in moderate and high seismic regions due to the uncertainty in the seismic performance of the substructure connections. Few ABC seismic connections were developed and have been demonstrated for potential use in high seismic regions. Among these is ultra-high performance concrete (UHPC) filled grouted-duct connection. The use of proprietary UHPC poses another challenge for wider implementation of this type of connection. The overall goal of this study was to develop non-proprietary, feasible alternative for the grouted-duct ABC seismic connection for precast bridge columns that can emulate the seismic performance of conventional CIP connections. Reducing the costs and using non-proprietary materials was the focus of this study to establish a less expensive, less restrictive alternative for UHPC-filled grouted-duct connections and avoid sole-source specification. In the first phase of this project and a companion study (Subedi et al. 2019), several non-proprietary UHPC mixes were developed and two were selected at the University of Nevada, Reno. They were used in 22 large scale pullout specimens to determine the bond behavior of UHPC-filled duct systems. Given their observed satisfactory performance, one of the non-proprietary UHPC mixes was further used and incorporated into UHPC-filled duct connections of two 42%-scale column models to connect the precast columns to footings. Both column models were tested to failure under combined axial and cyclic lateral loading to investigate their seismic performance and evaluate their ability to emulate the seismic performance of the CIP system. Moreover, analytical investigation for each column model was conducted to simulate the global response of the column models. The analytical studies were conducted using finite element computer program OpenSEES. Specific modeling assumptions for these connections that include the bond-slip effects in bars and ducts and bar debonding effects were validated for future implementation and further use in the design of this connection in actual bridges. Overall, non-proprietary UHPC-filled duct connections were successfully demonstrated to have acceptable seismic performance and are, in turn, recommended as suitable precast column-to-footing or column-to-cap beam connections for moderate and high seismic regions. Using such connection with the proposed UHPC mix can assure the formation of full plastic moment in columns without any connection damage.
Report No. CCEER 20-08