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CCEER-20-02: Seismic Studies Of Spliced Columns and Anchorage of Large Diameter Bars in Grouted Duct
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Accelerated bridge construction (ABC) refers to a bridge construction method that incorporates innovative techniques and materials to efficiently reduce construction time and traffic disruption. Grouted duct and couplers are some of the feasible connection types useful for ABC. The former is viable for both column-to-footing and column-to- cap beam joints. Precast members can be connected with grouted ducts in which member longitudinal reinforcements are anchored in ducts placed in adjoining members then the ducts are filled with grout. Grouted sleeve (GS) couplers and other types of rebar splicing devices are considered to be potentially effective connection types for ABC. In this joint type, each individual rebar is spliced by a mechanical coupler, which is readily located within one of the adjoining components, normally the precast component built at a precast plant. The majority of previous studies on grouted ducts have focused on No. 8 or smaller bars. Past research on spliced columns with grouted sleeves has utilized No. 8 bars or smaller. Bridge column longitudinal bars are typically larger, with No. 10 and No. 11 being very common. The objectives of this study were (1) to develop proof- tested, reliable embedment length design equations for grouted ducts with conventional grout anchoring mild steel bars, and (2) to study the cyclic response of columns with No. 10 longitudinal bars that are spliced in the plastic hinge using GS couplers. The project consisted of pullout tests of bars anchored in grouted ducts and testing of a precast reinforced concrete column model with grouted sleeve coupler followed by extensive analysis of columns with GS and other types of couplers. Twelve pullout tests were performed to understand the behavior of grouted vertical duct connections constructed using galvanized steel ducts, and to generate data to evaluate existing preliminary development length equations for bars anchored in grouted ducts. It was observed that the duct bond strength controls the grout-filled duct behavior and required bar embedment length when high strength grouts are used to fill the duct. It was also found that the existing equations for embedment length are conservative, which is highly desirable to prevent connection damage. The embedment length and mode of failure of bars anchored in grouted duct are sensitive to the combination of embedment depth, bar bundling, and eccentricity. The response is not sensitive to duct diameter or duct thickness for typical corrugated steel duct. To study the effect of using spliced large-diameter bars on the seismic response of columns, a half-scale column model utilizing GS couplers at column-to-footing joints was constructed and tested under cyclic loads. It was observed that the damage in the column incorporating grouted sleeve couplers was similar to that in CIP reinforced concrete columns under small and moderate levels of drift. However, the drift capacity was substantially lower, suggesting that GS couplers might not be appropriate for high seismic zones. Analytical studies of column with grouted sleeve couplers at column-footing connection were conducted using OpenSees and the results were compared with the experimental results. In addition to the grouted coupler, column models incorporating headed, swaged, and shear screw couplers were developed to compare the effects of using various types of couplers in the column. All four column models with different types of couplers exhibited similar response in terms of the maximum force, but the drift and displacement capacity varied depending on the coupler type. Compared to CIP, headed coupler reduced the ductility capacity by 6%. The reduction for grouted sleeve, swaged, and shear screw couplers was 30%, 22%, and 19%, respectively. The response of columns incorporating grouted sleeve coupler with No. 8 and No. 10 longitudinal bars were similar up to 5% drift, but the drift capacity was 6% when No. 8 bars were used.
Report No. CCEER-20-02