Abandoned Hole Effect on Ultimate Strength of Mechanical Anchors in Tension

Postinstalled anchors are frequently installed with unpredictable abandoned drilled holes (ADHs) at the job site. While ADHs may have a reducing impact on the original ultimate tensile strength (N_u) of the anchor per the design code, this effect was not adequately investigated. In this study, 60 wedge anchors in three diameters (d) and two (deep and shallow) effective embedment depths (h_ef) per d were tested in tension in five repeats. Half of the tests (30) served as the reference scenario for the other half (30) that included one ADH drilled at 2×d offset from the anchor. The ADH scenario resulted in (4.5–21%) reduction in N_u, regardless of the failure modes, and the percent reductions decreased as d and/or h_ef increased. Based on the results, an area method was proposed to predict the reduced N_u in the ADH scenario. This method can be used to predict reduced N_u when ADH conditions occur in the field and calculate the increased d and/or h_ef to minimize the reducing effect if the application allows.