Flexural behavior of retractable-cage prestressed pile segments under lateral loading: numerical and experimental investigation

Abstract
To address the construction limitations of conventional bored piles in confined environments, including complicated reinforcement splicing, low installation efficiency, and difficulty in quality control, a retractable reinforcement cage (hereafter, the retractable cage) prestressed bored pile (S-PC pile) system was developed. Unlike conventional prestressed piles and previously reported retractable-cage systems, the proposed pile adopts a post-tensioned reconfigurable reinforcement cage specifically designed for low-headroom construction conditions. A three-dimensional finite element model was established in ABAQUS to investigate the intrinsic flexural behavior of the pile segment under lateral loading. To isolate the sectional structural response, pile-soil interaction was intentionally excluded from the numerical model. The effects of longitudinal reinforcement ratio, stirrup spacing, prestressing level, and concrete strength on flexural performance were systematically evaluated. Parametric analyses showed that the longitudinal reinforcement ratio predominantly governs the ultimate flexural capacity and ductility of S-PC piles, whereas stirrup spacing and concrete strength have limited effects. Increasing the prestressing force from 50 to 150 kN increased the cracking moment by approximately 30%, but increased the ultimate moment by only 7% and reduced the ductility coefficient by about 60%. Based on numerical and experimental results, modified analytical expressions for the cracking moment and ultimate flexural capacity were proposed. The calculated-to-measured ratio for cracking moment improved from 0.76–0.90 to 0.82–0.95, while the prediction accuracy for ultimate flexural capacity improved from 0.67–0.97 to 0.80–1.04. Full-scale field tests demonstrated that the retractable-cage system significantly enhanced construction efficiency, achieving approximately eight times higher installation efficiency than conventional reinforcement cages. The proposed retractable-cage prestressed bored pile system provides an efficient solution for pile construction in confined environments and establishes a design-oriented framework for evaluating the flexural performance of reconfigurable prestressed pile systems.