Jonas Aparicio — PhD student in the MSA group of Laboratoire Navier — is defending his thesis entitled “Non destructive auscultation of exterior prestressing steel of concrete bridge"  on the 24th of January, 2024 at amphithéâtre Caquot, in the Coriolis building of the Descartes campus.

Summary

This work deals with the inspection of external prestressing cables and the various methods, applied or theoretical, for detecting faults in this type of cable. It is organised around three axes. The first axis aims to improve understanding of the state of a damaged cable and to understand the consequences of a given level of damage on the durability of the cable. It is based on a campaign of full-scale cable rupture tests, with cable damage reproduced by successive cutting of the wires making up the steel strands and numerical modelling of the damage. These tests highlighted the main mechanisms involved, such as the transfer of force from a broken wire to its strand and to the other strands in the cable, and the link between the quality of the containment provided by the grout and that of the transfer of force. Two models were proposed, linking the appearance of the damaged zone to the length affected by the breaks and to a conservative estimate of the stress loss. The second axis concerns the development of a method for distinguishing between healthy and damaged cables. The method is based on the measurement of the cable’s modal characteristics and is designed to be simple and quick to implement. Firstly, work was carried out to improve the method for determining the cable’s overall mechanical parameters, a prerequisite for detecting damage, by optimising the existing method. Indicators of cable damage were then proposed based on the results of cable rupture tests and analysed. This analysis shows that the proposed method offers advances but is not operational. The final axis concerns the development of an inspection method for locating, qualifying and quantifying any defects present in external prestressing cables. The method developed is based on the principle of radar, and a great deal of preparatory work has been carried out to enable the radar device to be used on the particular geometry of these prestressed cables. Finally, a prototype of a suitable antenna was developed and validated on models of cables with the types of defects found in external prestressing cables.