The application of the X-ray diffraction method in the assessment of PT bridges

The present research focuses on the application of the X-ray diffraction method as a non-destructive testing technique to evaluate the stress level in tendons of post-tensioned (PT) elements, such as the ones characterizing large-span infrastructures. The knowledge of the stress level can provide relevant information about the maintenance condition of PT structures, highlighting the possible presence of criticisms. The X-ray methodology investigates the stress state on the near-surface region of the element: the resulting measure is therefore strongly influenced by the presence of residual stresses, that need to be somehow estimated. Residual stresses are induced by the manufacturing process: wires and strands are produced by applying a cold-drawing process to high-strength steels; the thermo-mechanical treatment is realized by imposing continuous heating on tensioned specimens. This latter process reduces the relaxation of cables and relieves the residual stresses induced by the drawing, that are, however, generated. The present work aims to determine the main factors affecting the measures, with a particular focus on residual stresses.