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Embedment of cast-in-place anchors in concrete : minimum embedment depth / David Charles Willis.

by Willis, David Charles

Concrete construction -- Joints

Anchorage (Structural engineering)

104 leaves : ill. ; 29 cm.

Thesis advisor: Dr. John Zachar

Committee members: Dr. Hans-Peter Huttelmaier, Dr. Richard De Vries

Introduction -- Literature review -- The experiment -- The analysis -- Conclusions and recommendations -- References -- A: Anchor design calculations -- B: Pictures.

Anchor bolts have been a major building component for a long time. However, design of anchor bolts has only recently been introduced into building codes. ACI 318-02, Appendix D, presents the first building code requirements (for non-nuclear facilities) for anchoring to concrete. Anchor design is controlled by the lowest value of the applicable failure modes. For an anchor in tension, these include the steel strength of the anchor, the concrete breakout strength, the pullout strength, and the concrete side-face blowout strength. Splitting failure of the concrete must also be considered in design.

When the anchors fail as a result of the concrete, a sudden brittle failure is experienced. It has long been considered good engineering practice to design for ductility where possible. A ductile failure associated with the anchor steel does not produce a sudden rupture. This report explores the failure modes associated with a single anchor in tension in an effort to produce a recommendation for a minimum embedment depth of an anchor in concrete to assure the steel failure modes govern. Eighteen anchors made from 3/4" threaded rods were embedded in concrete as varying embedment depths. Some of the embedded anchors included a nut at the embedment depth, while the rest were embedded as plane threaded rod. A tensile load was applied to the anchors until failure.

The results of the anchor tests narrowed the range in which the embedment depth is sufficient to fully develop the steel strength of the anchor. Tests also showed that for short embedment lengths, the headed and non-headed threaded rods failed at similar loads. Although threaded rod appears to be closely related to deformed bar, the development and interaction with concrete proves to be much closer to plane steel bars. Analysis suggests that bond strength between the concrete and the anchor play a critical role in the ultimate strength of the anchor.

Establishing a minimum embedment depth for a steel anchor would allow for engineers to provide quick and economical anchor design with added confidence. A steel controlling failure mode design would incorporate the ductile elastic properties of steel into all anchor designs. With additional testing and analysis, an established relationship between the anchor type, anchor size, and concrete strength could be developed to establish a minimum embedment depth for anchors in concrete.

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