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CCEER-15-07: Design and Construction of Bridge Columns Incorporating Mechanical Bar Splices in Plastic Hinge Zones
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Accelerated bridge construction (ABC) relies heavily on prefabricated reinforced concrete members. One method to connect prefabricated columns to footings or cap beams is through the use of mechanical bar splices commonly referred to as couplers. Even though current seismic codes prohibit application of couplers in the plastic hinge area of columns located in moderate and high seismic zones, recent studies have revealed the feasibility of precast columns utilizing couplers in the plastic hinge zones helping expand ABC in this zones. Several types of mechanical bar splices each with a unique performance and anchoring mechanism are available in the U.S. market. Five of these were included in this study: shear screw, headed bar, grouted, threaded, and swaged couplers. A state-of-the-art literature search was conducted to compile and interpret data on the seismic performance of these coupler types as well as columns incorporating these couplers in the plastic hinge zones. Findings were summarized and tabulated. Subsequently, coupler acceptance criteria for seismic applications and acceptance criteria for ductile columns incorporating couplers is plastic hinges were developed. Then the seismic performance of the couplers and the columns was evaluated. It was found that the coupler performance varies for different loading rates and even for the same type of coupler produced by different manufactures. Furthermore, location of the coupler in columns was critical for large size couplers. Special detailing was studied by different researchers to achieve large displacement capacities. Satisfactory performance was usually observed for small size couplers in which their location had insignificant effect on the column seismic behavior. Findings from the literature study as well as the coupler evaluation indicated that a rigorous testing schedule is needed to completely understand the seismic performance of each coupler type and series. Constructability and speed of construction for each coupler type were also studied. It was found that the application of mechanical bar couplers at both ends of precast columns will shorten the construction time by approximately 60% for a three-column bent regardless of the type of the coupler. Since conclusive trends could not be established with limited test data, an extensive parametric study was carried out to investigate coupler effects on the column seismic behavior. A generic stress-strain model was also developed to represent behavior of all types of couplers. It was found that the coupler length, the coupler location, and the rigidity of the coupler significantly affect the displacement ductility capacity of mechanically spliced columns. Furthermore, a simple design equation was developed in which the spliced column displacement ductility capacity can be estimated based on the basic characteristic and geometry of the coupler and the column. Finally, a design guideline as well as examples were developed to facilitate field deployment of precast columns incorporating mechanical bar splices.
Report No. CCEER-15-07