Effects of compressive and tensile fields on the load carrying capacity of headed anchors.

Abstract

The results of research initiated in the early 1980s led to the replacement of plasticity-based design guidelines for the load-carrying capacity (concrete breakout) of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions are available in the design codes that account for the presence of tensile fields causing concrete cracking, no provisions are available for anchors embedded in prestressed concrete. This thesis presents the results of linear and nonlinear elastic fracture mechanics analyses of the progressive failure of headed anchors embedded in a concrete matrix under compressive or tensile prestress. In addition, and because of the complete lack of experimental evidence, the results of a relatively large experimental investigation of the behavior of headed anchors embedded in compressively prestressed concrete are presented. Discrete crack finite element models and experiments predict an increase (decrease) in load-carrying capacity and post-peak dissipated energy with increasing compressive (tensile) prestress for all the embedment depths investigated. For extremely shallow cases, in which the embedment depth is less than the (typical) maximum aggregate size of concrete, it is shown that deterministic continuum-based models are not applicable. Overall, the results show that there is very little difference between the linear elastic and nonlinear elastic fracture mechanics approaches, this implying that the concrete breakout strength is governed by the strongest possible size effect. In addition to providing analytical support to the existing design approaches for the capacity of headed anchors embedded in cracked concrete (under tension), the present work provides an experimentally and analytically based preliminary easy-to-use design formula for the concrete breakout capacity of headed anchors in compressively prestressed concrete.