ANALYZING THE FAILURE MECHANISMS AND DEVELOPING STRENGTH PREDICTION MODELS FOR CONCRETE EXPANSION AND SCREW ANCHORS IN TENSION
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Concrete anchors serve as the connections between structural elements in various applications in concrete structures. This dissertation focused on investigating two popular post-installed mechanical anchors, torque-controlled expansion (TCE) anchors and screw anchors, and their common failure modes. TCE anchors commonly fail in a Pull-through mode when installed at deep effective embedment depths (hef). Screw anchors typically fail in a Combined mode of Pull-out and Concrete breakout modes. However, research on these failure modes are scarce and no design model is available to predict the ultimate tensile strength (Nu) of these failure modes in the current design codes. A total of 128 tension tests on TCE anchors from 3 manufacturers in 3 diameters were tested in 2 hef per diameter. Both failure modes and Nu are found dependent on hef and diameter. Using ABAQUS, finite element models (FEM)s of TCE anchors were developed and matched well with the test results regarding failure modes, load-displacement behavior, and ultimate strength. Total of 144 tension tests on screw anchors from 3 manufacturers in 3 diameters and 2 hef per diameter were conducted. Approximately 80% of the tested anchors failed in the Combined mode and Ncomb was found linearly correlated to hef1.3 but slightly dependent on anchor diameter. FEMs were also developed for screw anchors. Combine failure mode was observed for both deep and shallow embedment depths. Good agreements were found in load-displacement behavior and Ncomb between FEMs and test results. Based on parametric studies using additional FEM simulations, prediction models for predicting Nu of the pull-through mode of TCE anchors and Combined mode of screw anchors, individually, was developed and showed good agreements with the test results. Post-installed anchors are frequently installed with abandoned drilled hole (ADH)s at the job site. Total of 60 TCE anchors were tested at two scenarios of hole conditions: 1) reference (no hole), and 2) one ADH drilled at 2×d offset. The ADH scenario resulted in (~4.5-21%) reduction in Nu, regardless of the failure mode, and the percent reductions decreased as diameter and/or hef increased. An area method was developed to predict the reduced Nu in the ADH scenario.