Investigation of post-construction stress distribution and influence of deficiencies in post-tension system.

Stress losses in tendons of post-tensioned bridges not only significantly impact their structural performance but also pose risks to their serviceability state and overall integrity over time. These losses can lead to a reduction in structural capacity due to decreased prestress force, increased deflection under load, and the development of cracks compromising structural integrity. Furthermore, they contribute to a loss of structural redundancy and heightened vulnerability to dynamic loading effects such as fatigue and damage. This research aims to investigate the implications of such damage during both construction and operational lifespan of a post-tensioned bridge located in northern Italy, highlighting the crucial factors affecting its long-term performance and safety. Specifically, the author aimed to identify and quantify the consequences of progressive tendon damage during both construction and service life, to establish potential causes of failure, and to predict the bridge's current state and remaining lifespan. These objectives were addressed through a comprehensive approach involving simulation of a replica bridge using Finite element modelling. Various scenario tests were conducted to reflect real-life damage and stress loss in tendons, including stress losses due to friction, concrete instantaneous deformation, and long-term relaxation of the tendons. Additionally, scenarios accounted for corrosion and pitting effects. To ensure the accuracy and reliability of the data, extensive verification was undertaken through both hand calculations and comparison with data from previous research works. After conducting extensive simulations on the bridge, it was determined that immediate stress losses, comprising friction losses and losses due to concrete instantaneous deformation, in addition to long-term losses, affects the serviceability state of the bridge after 55 years. Regarding corrosion effects, it was found that it takes over 100 years for sufficient diffusion of chlorides into the concrete at the tendon level to initiate corrosion. In cases of execution errors leading to water seepage into tendon ducts, corrosion was considered to begin immediately, resulting in the initiation of tendon area loss due to pitting. when stress losses are combined with pitting effects, the most conservative scenario indicates crack initiation after 29 years. The harvested data played a crucial role in understanding how the bridge behaves in different situations, giving us valuable insights into its structural response and expected lifespan.