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Cast-in-drilled hole (CIDH) shafts are frequently used to support reinforced concrete bridge columns because they have smaller footprints as compared to spread footings. The use of enlarged (Type II) pile shafts has additional advantages in that they provide more tolerance in pile positioning and also prevent the formation of below-surface plastic hinges in the piles in the event of a severe earthquake. The latter will lead to easier post-earthquake damage inspection. According to the specifications of the California Department of Transportation (Caltrans), the diameter of a Type II shaft shall be at least 610 mm (2 ft) larger than the cross-section dimension of the column. Hence, the column reinforcement extended into a pile shaft forms a non-contact splice with the shaft reinforcement. Because of the lack of information on the performance of these splices, the seismic design specifications of Caltrans on the embedment length of column reinforcement terminating in a Type II shaft are very conservative, especially for large-diameter columns. This complicates the construction work and increases construction costs.

This report presents an experimental and analytical investigation to determine the minimum embedment length required for column longitudinal reinforcement extended into a Type II shaft and the transverse reinforcement required in the bar anchorage regions of these shafts. Experiments were carried out to investigate the bond strength and cyclic bond deterioration of large-diameter bars (No. 11, 14, and 18 bars), which are frequently used in large-diameter bridge columns and piles, and to evaluate the adequacy of the development length …