Pull-out behavior of bonded anchors in UHPC thin plates

An anchored substrate that is too thin can exacerbate stress concentration caused by drilling, leading to cracking. But fibers in concrete will organize the propagation of cracks. The coupling of the two factors will affect the size effect of the substrate in the thick direction. Therefore, it is necessary to reevaluate the new behavior of anchoring in Ultra-High-Performance Concrete (UHPC) thin plates. This study conducted 30 unrestricted pull-out tests on the bonded anchors in UHPC thin plates and discussed the effects of different substrate thicknesses( t o ), embedment depths( H ef ), anchor diameters( D ), embedding methods(whether "fully embedded" or not), and drilling methods on the pull-out behavior. The test results show a direct correlation between the aspect ratio( H ef /D ) and failure modes, with failure modes shifting from PO to CO/CB, and then from CB to SP as H ef /D increases. Moreover, the threshold for failure mode transition is much lower than the empirical value in normal concrete(NC), such as H ef /D ≈ 2.53 when CB dominates. The non-linear exponential correlation between bearing capacity( N u ) and H ef is more significant; N u is proportional to H ef 1.8 . The back plate "cone explosion" caused by drilling has little effect on the failure mode, while it can reduce the H ef by an average of 20%, which significantly weakens N u . Furthermore, a finite element model(FEM) of UHPC thin-plate anchors was established to analyze the pull-out failure mechanism, particularly confirming the failure mode and bearing capacity difference mechanism caused by the loss of bottom tensile stress( σ t ) in the "fully embedded" group. Finally, a new model was developed based on experimental results to predict the pull-out bearing capacity of anchors in UHPC thin plates, which quantified the impact of "cone explosion", except for shallow depth scenarios, its predictive reliability is good.