Flexural Capacity of Micropile Threaded Connections
Published: 2025
Publication Name: TIDC
Abstract:
This report investigates the flexural behavior of threaded micropile connections under pure bending and combined axial compression and bending, with emphasis on joint-level kinematics and failure mechanisms that are not explicitly addressed in current design practice. A coordinated program of full-scale four-point bending tests, augmented with high-resolution digital image correlation, was conducted to characterize strain localization, joint seam separation, and governing failure modes. Results from pure bending tests demonstrate that flexural capacity is controlled by localized tensile-driven joint kinematics, with failure occurring through jump-out or rupture depending on joint geometry. Combined loading tests reveal that axial compression can delay joint separation and increase flexural capacity, contrary to conventional axial–flexural interaction assumptions. For the axial load range examined, combined loading increased flexural capacity by an average of approximately 15% relative to pure bending. Building on these observations, a mechanics-based analytical framework was developed to predict joint flexural capacity under combined loading by explicitly accounting for joint kinematics. The proposed approach justified higher flexural capacities—on the order of 20–60% relative to conventional design predictions for the loading conditions investigated—while remaining generally conservative, and provides a more physically consistent basis for evaluating threaded micropile connections subjected to bending and combined loading.