Experimental Evaluation of Fire Resistance and Postfire Mechanical Behavior of Cables with Multiple Fire Protection Strategies

As critical components of cable-supported bridges, bridge cables face significant threats from elevated temperatures induced by fire accidents. This study developed a specialized fire-furnace test to evaluate the postfire performance of eight specimens, including five 109-strand and three 55-strand cable specimens, combining elevated temperature and stress. During the eight fire-furnace tests, heating duration, cable diameter, and fire resistance measures were systematically considered. Having finished fire-furnace tests and been cooled naturally to ambient temperature, tensile and fatigue tests were performed to assess the residual mechanical properties of the cables. Test results indicate that combustion of the polyethylene (PE) sheath significantly accelerates heat transfer to the outer steel wires, leading to a rapid temperature rise and greater temperature difference across the cable cross section. This thermal effect contributes to more severe structural damage, demonstrating that PE is not a suitable material for fire protection in cable systems. Mechanical performance tests conducted after high-temperature exposure revealed that the elastic modulus remains nearly unchanged when the peak temperature is below 600°C but exhibits a sharp reduction once the temperature exceeds 600°C. However, the yield and ultimate strength decrease to approximately 22% and 31% of their initial values, respectively, until the average temperature arrived at 800°C, and then grow to around 25% and 35% as the temperature continues to rise to 920°C. In addition, the fatigue life reduces at least 75% of the initial value as the temperature grows to around 600°C. Ceramic fiber tape with thicknesses of 6 and 3 mm has been recommended as one of the most effective fire resistance measures for specimens with 109 and 55 steel wires, as they can control the temperature rise with higher efficiency.