Numerical Study of Bond and Development of Column Longitudinal Reinforcement Extended into Oversized Pile Shafts

Abstract

This paper presents a numerical investigation to examine the bond-slip behavior of column longitudinal reinforcing bars embedded in oversized pile shafts and to determine the minimum embedment length required for the column bars to prevent anchorage failure. Three-dimensional nonlinear finite-element models of column-pile assemblies incorporating the bond-slip behavior of the longitudinal reinforcing bars have been developed for the numerical analyses. The capability of the models in capturing the response of column bars along their embedment length has been verified with experimental results from four full-scale column-pile assemblies tested under cyclic lateral loads. The study has shown that the bond-stress distribution along the bar anchorage length is highly nonuniform and that the embedment length specified for the column reinforcement in current design standards is very conservative. A new design formula that significantly reduces the embedment length has been evaluated. The numerical results have indicated that the new embedment-length formula provides a good margin of safety against the pull-out failure of the column bars. The results have also shown that the use of an engineered steel casing to provide lateral confinement for the pile is an effective means to enhance the bond strength and reduce the slip of the column longitudinal bars in the anchorage region.