Residual Fatigue Performance of Stay Cable Strands Subjected to Fire Threats

Fire-induced extreme temperature events can rapidly degrade the fatigue capacity of stay cable strands. This paper investigates the residual fatigue performance of fire-exposed stay cable strands to help bridge owners assess whether a cable-stayed bridge can remain in service during emergency repairs. Furthermore, this study assesses various strand gripping methods for fatigue testing of strands. To achieve the objectives of this study, high-density polyethylene–protected ASTM A416/A416M seven-wire strands were extracted from two larger bridge cables that underwent fire-protection qualification tests. The strands were categorized into three damage states based on a visual classification of the severity of damage, including charring of the outer sheathing, burning of internal lubricant between the strands, and surface rust on the strand wires. Although some subjectivity was observed in the visual classification, fatigue testing results, subjected to the fatigue loading protocol recommended in PTI D45.1, showed a near-linear degradation in fatigue life, compared to the damage state. Further, the fracture surface morphology under scanning electron microscopy demonstrated this trend, where lower damage showed typical fatigue fracture patterns and higher damage resulted in an increasing presence of tension fracture patterns.