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Seismic Studies of Superstructure and Substructure Connections for Accelerated Bridge Construction
AdvisorSaiidi, M. Saiid
Civil and Environmental Engineering
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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. Prefabrication of bridge components is one of a highly effective ABC method. The prefabricated elements must be connected to form a well-integrated bridge system. Connections of prefabricated elements are particularly critical in moderate and high seismic zones. The prefabrication may be done at both the superstructure and substructure levels. This study focused on two types of connections: superstructure connections (deck to girder), and substructure connections (column to footing). An experimental study on superstructure connections was carried out to evaluate the shear, pullout strength, and stiffness of the selected headed anchors for deck to girder connections. Various parameters such as group effect of anchor, types of grout, and head area of the anchors were also studied. The results indicated that the type of grout and head area of the anchors had an insignificant effect on the shear and pullout capacity of the anchor. It was concluded that the current provisions in the AASHTO LRFD Specifications for the ultimate shear strength of studs in CIP construction may be used for anchors in precast R/C panels. Two types of substructure connections, grouted sleeve and grouted duct connections, were studied utilizing bar sizes that are used in the field. 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 of 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. 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. The duct bond strength controlled 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. An analytical investigation of a two-span bridge was carried out to determine the forces in the superstructure connections when subjected to large ground motions. A computational model for headed anchors was used to investigate the seismic response of decks with rigid shear links between the deck and girders and flexible links with shear pockets spaced at 4 ft and 6 ft spacing. In addition, the nonlinear response history analysis was performed for eight earthquake ground motion intensities corresponding to 100% and 150% of the design level. Insignificant difference was observed in the dynamic properties of the bridge and seismic behavior due to the increase in pocket spacing from 4 ft to 6 ft. It was also found that the forces in the headed anchors for both spacing were well below ultimate strength of the connectors leading to deck connections being capacity protected. Analytical studies of the 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, analytical 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 column 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.