Post installed rebar end anchorages in reinforced concrete structural connections

Abstract

This thesis is an attempt to integrate the different available perspectives for rebar end anchorage design in general and post installed rebar in particular, and work towards a general framework for design of end anchorage zones in reinforced concrete (RC) connection applicable irrespective of the detailing (straight or with bends) and type (cast-in or post installed) of the connection. It builds on comprehensive discussions of the current state-of-the-art consideration of anchorages in reinforced concrete construction. The discussions are aligned in a way to highlight the diversity of the different perspectives of assessment and design of rebar end anchorages and at the same time identify the context in which the perspectives could be integrated. The mechanical state of loading and the possible load resisting mechanisms are identified as pivotal for this purpose, and hence provide the rational background platform necessary for comparison of different approaches for assessment of rebar end anchorages. The differences in the assessment approaches are better understood in the light of the possible load resistance mechanisms and the potential of the models used for their realistic assessment. The system (or product) specific definition of bond resistance in fastenings technology in contrast to the general empirical definition of bond resistance in conventional RC practice is found to be one primary aspect responsible for the evident differences in the assessment approaches. The recent developments of system specific models for bond resistance coherent with RC practice (PO+SP model framework) that resulted from research projects conducted at IWB, University of Stuttgart, Germany are discussed. These models form an important input for the general assessment framework for rebar end anchorages based on failure hierarchy of all possible load resisting mechanisms (the Failure Hierarchy (FH) approach) developed in this thesis. The different mechanics in RC connections: column-foundation joints (CFJ), wall-foundation joints (WFJ) and beam-column joints (BCJ) strongly affects the behaviour rebar end anchorage zone. Hence a possibility of connection specific consideration in assessment of the rebar end anchorage zones is identified based on the discussion of the available response database in literature for the different joint types. This thesis develops an assessment framework (Failure Hierarchy Approach) for realistic evaluation of rebar end anchorage zones giving due consideration to (i) system specific characteristics of different types of anchorages (cast in and post installed) and (ii) different possible mechanical states of the connection (CFJ, WFJ, BCJ). A need for generating benchmark test data for observing the transition of different failure modes possible in rebar end anchorage zones is highlighted in these discussions. To this end, the design of test specimens is performed for obtaining response database specific to the range of parameters over which a transition of different possible failure modes in the rebar end anchorage zones can be observed. The test program on column-foundation joints provides the necessary database for overall validation of the FH approach. A comparison of different assessment approaches in the light of test results from this thesis and from the literature show the potential of the FH approach for realistic assessment of the behaviour of rebar end anchorage zones in RC connections. For highlighting the importance of connection specific consideration, experiments on wall-foundation joints and beam-column joints are conducted. The generated database provides useful insights towards harmonization of co-existing concrete failure theories. The thesis concludes with an overview of the extent to which the objective of development of general assessment framework for rebar end anchorage design could be reached. Contribution from this thesis towards design concepts for rebar end anchorage anchorages are discussed. The thesis closes with open questions that need further investigations and recommendation for the way forward based on insights it has developed.