Effect of wire rupture on the mechanical behaviour of an external prestressing tendon

External prestressing is a construction technique widely employed since the 1980s for large civil engineering structures to reduce the cross-sectional area of structures and thus their permanent load, and more recently to reinforce structures. External prestressing tendons are composed of strands, each comprising 7 wires with a very high elastic limit, laid in a HDPE sheath, anchored in reinforced concrete blocks and generally tensioned to 80% (excluding creep and shrinkage) of their ultimate tensile strength. To safeguard the cables, grout was injected into the sheaths. However, this protection system has not always prevented the corrosion of the strands. When wires and strands re-anchor through friction in the grout after fracturing due to corrosion, the stress on the remaining tendon increases until the breaking load of the entire tendon is reached. The sudden release of energy from such a break can jeopardize the structure and endanger any personnel present on-site. Therefore, understanding the state of the cable at a given level of degradation and the permissible degradation before failure is crucial for structure managers. Several 46 m long cables between supports were tested and brought to failure by the progressive cutting of the wires composing the strands. Initially, three tendons, each comprising a single strand of seven wires, were tested. Subsequently, three tendons, each comprising five strands, were examined. The experiments conducted and the analysis of the results have enhanced the understanding of the evolution of tension in the tendon as it becomes damaged. To this end, a model was developed to estimate the length affected by wire ruptures. This work also presents findings regarding the transfer of stresses within the tendon and strands resulting from these ruptures. Finally, a model that estimates tension loss due to the sliding of wires after they break is presented.