Prestress Loss and Bi-Directional Prestress Effect of a Large-Span U-Shaped Aqueduct: Field Test and Numerical Analysis

Prestress loss and bi-directional prestress effects are critical design parameters that determine the bearing capacity of large-span U-shaped aqueducts. Based on a 42 m span simply supported U-shaped aqueduct, the pipeline friction coefficients were tested through least-squares fitting and validated against a finite element analysis model. The results revealed pipeline friction induced 4.82–5.08% longitudinal and 35.84–39.23% circumferential prestress loss, with 12-month post-tensioning monitoring showing 9.84% (longitudinal) and 3.15% (circumferential) long-term loss. Maximum concrete compressive stresses reached 5.83 MPa (inner wall) and 7.14 MPa (outer wall) under empty groove conditions. Six prestress tensioning sequences were numerically compared to identify the optimal “both ends to center” circumferential tensioning scheme. The prestressed tendon layout was optimized by increasing circumferential tendon spacing from 40 cm to 60 cm while maintaining global compression. This research provides a systematic framework for prestress optimization in curved concrete structures.