Bridging the gap between design provisions for connections using anchorage or Strut-And-Tie models

Bonded anchors consist of steel elements (e.g. threaded rods) which are bonded into a drilled hole by a prequalified adhesive mortar. They are designed according to ACI 318 Appendix D “Anchoring to Concrete”. Reinforcing bars post-installed in drilled holes by a suitable mortar behave like cast-in reinforcing bars. They are designed according to ACI 318 Appendix A “Strut-and-Tie-Models” in connection with Chapter 12 “Development and Splices of Reinforcement”. In a connection (e.g. concrete column to a foundation) cast-in or post-installed reinforcing bars transfer the tension force of the connected concrete structural member into the base member. This is also done by bonded anchors if a steel member is connected to a concrete structure. When assuming that the bond strength of cast-in or post-installed bars and of bonded anchors is about the same the required embedment depth of connections with straight reinforcing bars and bonded anchors should be about the same independent, if the connection is designed according to Appendix A or Appendix D. However, in many applications this is not the case. In the paper tests on column-foundation connections under monotonic and cyclic loading performed by the authors at the University of Canterbury are described. Used were cast-in hooked and straight deformed reinforcing bars and post-installed reinforcing bars. The measured failure loads are compared with predictions according to ACI 318, Chapter 12 (development length) and Appendix D (anchorages). Based on the results of the evaluations it is proposed to design connections of concrete members according to Appendix D and to amend the provisions in Chapter 12 and Appendix D to achieve a better agreement of the design results when using the two design models.