On Robustness of Post-tensioned Concrete Bridges in Case of Tendon Failure

This dissertation investigates the robustness of post-tensioned and post-grouted concrete bridges in the event of tendon failure, with a focus on the structural behaviour, reliability, and safety implications of such failures. The study addresses the growing concern over aging infrastructure, particularly in environments where corrosion-induced tendon degradation and evolving traffic loads pose significant risks to structural integrity.

The research is presented through five peer-reviewed publications, each of which contributes to a comprehensive understanding of robustness from local bond behaviour to system-level performance. It has been demonstrated through experimental studies that tendons are capable of re-anchoring even in incompletely grouted ducts. However, this process is accompanied by a substantial increase in re-anchoring lengths and a modification in force distribution. These findings have been integrated into analytical models that extend existing bond-slip theories to account for multistrand tendons in grout and in defective grouting.

At the member level, full-scale beam tests demonstrate that post-tensioned structures can exhibit ductile, observable failure modes through moment redistribution and plastic hinge formation, even after localized tendon failure. Reliability analyses show that original design choices, particularly the conservative serviceability limit state (SLS) criteria—enhance cross-sectional redundancy and robustness. Additionally, a calibrated traffic load model based on Finnish monitoring data highlights the impact of increasing axle loads and the effects of convoys of lorries on structural safety margins.

The dissertation proposes a multi-level framework for robustness assessment, encompassing local tendon behaviour, structural redundancy, and evolving external demands. The findings support the development of improved assessment methodologies, design guidelines, and maintenance strategies for post-tensioned bridges, with practical implications for engineers, asset managers, and policymakers.