Cast-in and post-installed rebar anchorage systems in RC column foundation joints: System specific assessment and design

Abstract

For assessment and design of post installed reinforcing bar (rebar) anchorages in reinforced concrete (RC) construction, two different approaches (i) conventional RC approach and (ii) fastening technology approach, coexist. For high strength adhesive systems, it is likely that the design anchorage lengths obtained using the fastening technology approach are significantly smaller in comparison to that obtained using the conventional RC approach. The main reason for this gap between the two approaches is, that while conventional RC approach considers qualified post installed (PI) systems as equivalent to cast in straight systems (CIS), PI systems are considered to be system specific in fastening technology. The system specific consideration of PI rebar anchorages in fastening technology makes it possible to take advantage of the higher bond strengths of the innovative adhesive systems, which is not possible in conventional RC design.This paper considers a comparison of the available approaches for assessment of rebar end anchorages in RC column foundation joints (CFJ). To this end, the benchmark test data generated by the authors [1] is used for the comparative discussions in the background of possible modes of failure. To include system specific definition of bond resistance in conventional RC approach, the potential of the system specific bond model in fastening technology to replace the general bond model in conventional RC practice for rebar anchorages is discussed. The alternate possibility of evolving the existing bond model in RC practice for including system specific consideration is also discussed. It is observed that the system specific definition of bond resistance within the framework of RC design practice is more suitable for rebar end anchorages. A proposal for failure hierarchy based assessment approach employing this system specific definition is made in this paper. The proposed approach is successfully validated to demonstrate its capability to assess both the failure loads and failure modes in a realistic manner, irrespective of the type of anchorage (cast in or post installed). The proposed approach is in concurrence with RC design practice and at the same time does not conflict with fastening technology. The presented is thus, a comprehensive breakthrough towards harmonizing the coexisting design concepts for rebar end anchorages.