The effect of external confinement on flexural hinging in drilled pile shafts

Six one-third-scale CIDH pile shafts were tested to simulate the subgrade moment pattern in an in situ pile shaft. The test fixture could also simulate the presence of external confinement provided by soil. Three levels of transverse reinforcement were tested. Three piles were tested with external confinement, and three without. The presence of external confinement played a significant role in enhancing flexural ductility by supporting the confining action of the transverse steel reinforcement. The presence of external confinement also increased the plastic hinge length, significantly reducing local curvature demand by allowing the hinge rotation requirements to be spread over a greater length of the pile shaft. In the absence of external confinement, the transverse reinforcement levels specified under current column design guidelines provided adequate flexural ductility for seismic response.