Development of Bridge Column Longitudinal Reinforcement in Oversized Pile Shafts

This paper presents an experimental investigation to determine the embedment length required for longitudinal reinforcement in a bridge column extending into an oversized pile shaft, and the amount of transverse reinforcement required for the pile shaft to prevent premature bar anchorage failure due to concrete splitting induced by bar slip. Four full-scale column-oversized pile assemblies were tested under quasi-static cyclic lateral loading. The test specimens had different embedment lengths for the column reinforcement, different amounts of transverse reinforcement in the piles, different sizes of longitudinal bars, ranging from No. 8 to No. 18 (25 to 57 mm) bars, and different column-to-pile diameter ratios. All column-pile assemblies behaved in a ductile manner with plastic deformation occurring near the base of the columns despite some cone-shaped fractures and tensile splitting cracks occurring in the top portion of the piles. The test results show that the embedment length for the column reinforcement can be significantly reduced as compared to that required in current design specifications. The study also shows that an engineered steel casing designed according to a formula proposed here can effectively confine the pile shaft and significantly reduce splitting cracks.