Behavior of anchorages with anchor reinforcement under different loading conditions

Anchorages are used in reinforced concrete structures to transfer different types of loads from structural or non-structural connection elements into concrete. Depending on the application of the anchorage, various loading conditions, such as tension, shear, bending moment, etc., can be induced on an anchorage. Failure of an anchorage under these loading conditions can manifest in different modes, such as steel failure, concrete breakout failure, splitting failure, etc. This work is primarily focused on the concrete breakout failure of anchorages. Concrete breakout failure of an anchorage is brittle in nature, leading to a brittle response of the anchorage connection. Typical methods to improve the breakout strength of an anchorage are not always plausible due to design constraints. Under such conditions, anchor reinforcement is typically utilized. Anchor reinforcement provides a stitching effect between the breakout body and the structural body. Existing design models in codes and standards to design anchor reinforcement, such as ACI 318, EN 1992-4, fib Bulletin 58, etc., are either overly conservative or unconservative, depending on the amount of anchor reinforcement provided. Existing models for the design of anchor reinforcement for certain design conditions, such as eccentric loading and seismic loading, either do not address these design conditions or suffer from similar shortcomings. Post-installed anchorages are utilized in numerous retrofitting and strengthening applications for reinforced concrete structures. However, existing design models either do not address post-installed anchorages or provide a rather conservative or unconservative design. To address these shortcomings in the design models, an extensive experimental investigation was performed on cast-in and post-installed anchorages subjected to tension, shear, and moment loading in this work.Post-installed anchor groups, including bonded, undercut, and expansion anchors, strengthened with cast-in anchor reinforcement, were tested under static and cyclic tension loading. In addition to that, cast-in anchorages strengthened with cast-in anchor reinforcement and subjected to eccentric tension loading were also tested. These test results were further utilized to validate the 3D-FEA models developed using Macroscopic Space Analysis (MASA), which utilizes a micro-plane model as a constitutive law for modeling concrete. Following that, a numerical parametric investigation was conducted to investigate additional parameters for cast-in anchorages subjected to eccentric tension loading. For shear loading, post-installed bonded anchor groups, located close to a concrete edge and subjected to static and cyclic shear load towards the edge, were strengthened with post-installed anchor reinforcement bars. In addition to that, cast-in anchor groups strengthened with cast-in anchor reinforcement and subjected to eccentric shear load towards the edge were also investigated. 3D-FEA models were validated using test results to investigate additional parameters further. Anchorages subjected to bending moment resist the applied load by a tension-compression couple developed by the tension forces on anchors and compression between the concrete and the anchor baseplate. The investigation on moment loading on anchorages was focused on post-installed undercut anchor groups strengthened with post-installed anchor reinforcement and subjected to cyclic bending moment loading. The test data was utilized to validate the 3D-FEA models to further investigate additional parameters.By utilizing the test data and additional data generated using 3D-FEA, a holistic design model is proposed. The proposed model can be utilized to design anchorages with anchor reinforcement under tension, shear, and moment loading. In addition to that, the proposed design model can be used to design anchor reinforcement subjected to eccentric tension and shear loading. The scope of the model includes both cast-in and post-installed anchor groups and anchor reinforcement. Results show a significant improvement in the design strength provided by the proposed model compared to existing design models. The proposed design model also predicts the failure mode accurately. The proposed model introduces an upper limit of strut failure to limit the increase in strength for cases with a high amount of anchor reinforcement, thus resolving the unconservative nature of existing design models.