Effects of Minor Anomalies on Axial Capacity of Drilled Shafts

Because of their visually unexposed locations and method of construction, drilled shafts often are constructed with minor anomalies, consisting mainly of small voids, mispositioned rebar cages, and corroded rebars. Anomalies can occur even with acceptable quality controls; hence, their existence must be incorporated into the design process. Laboratory tests were used on scaled reinforced concrete shafts in axial compression to quantify the extent of loss in compressive capacity caused by the presence of various anomalies and to investigate the amount of loss in stiffness and effect of confinement on the ductility and stiffness of model shafts with anomalies. Considered variables included the shape and length of the void, spiral spacing, rebar corrosion, and steel cage offset. Analysis of the test results showed that the presence of a void within the cross section affects both the compressive strength and the ductility of a shaft. The effect on the ductility, however, is more critical, particularly when the void extends inside the core of the shaft. Corrosion of the longitudinal rebars through a void significantly reduces the strength and ductility. However, slight cage offsets that are within the tolerance of the construction specifications have only a minor effect on the structural performance. The results of the laboratory tests will be used in future papers, along with further laboratory tests, field observations, and simulations, to derive and recommend rational structural resistance factors for drilled shafts that will be separate from those for structural columns.