Integrated field assessment of residual prestress and tendon rupture response in a post-tensioned concrete bridge

This study presents an on-site framework for quantifying residual prestress in prestressed concrete bridges using concrete strain-release measurements from the strain-isolation (saw-cut) method, targeted non-destructive testing (NDT), diagnostic load testing, model calibration, and independent steel-based reference measurements. The framework was applied to the Autio Bridge, a continuous post-tensioned concrete bridge in Sweden built in 1963 and investigated during its 2025 demolition campaign. Ground-penetrating radar, ultrasonic pulse velocity, and half-cell potential measurements supported geometric refinement, material-condition assessment, and interpretation of the saw-cut tests. Measurements from a controlled diagnostic load test were used to calibrate the finite element model and determine parameters for stress back-calculation. Saw-cut estimates were compared with wire-cutting and X-ray diffraction (XRD) measurements on the prestressing steel. Relative to an initial anchorage force of 975 kN, estimated prestress losses were 7–11% from wire cutting, 4–9% from XRD, 14% from saw-cutting, and 26% from the Eurocode calculation. The saw-cut estimate of 839 kN was interpreted as conservative due to incomplete strain isolation. Controlled wire cutting, monitored by acoustic emission (AE), wire strain gauges, and micro-electro-mechanical systems (MEMS) inclinometers, linked tendon rupture to measurable global bridge response, demonstrating the value of integrating complementary measurements.