Experimental study on the fire performance of prestressed steel parallel wire strands

Bridges are critical components of the transportation system and any damage to these structures can result in important social and economic consequences. The literature concerning design standardization for fire hazard in suspension bridges is limited. High strength prestressed steel cables serve as main load-bearing components for suspension bridges, and exposure to high temperatures may result in their prestress loss, leading to structural failure. This paper experimentally investigates the fire performance of 19-parallel wire strands (PWS cables) with a tensile strength of 1860 MPa used as suspender cables in long-span suspension bridges. PWS cables were prestressed and then subjected to UL1709 hydrocarbon fire and simulated open pool tanker fire scenarios in the gas furnace until failure. The load-deflection plots of PWS cables suggest that the cables at ambient temperature sufficiently withstood 95% of their ultimate load capacity. However, the unprotected PWS cables failed within 3-8 min in the fire tests but still sustained the load at 400 degrees C, which confirms the conservative estimation of 300 degrees C critical cable temperature mandated by the Post-tensioning Institute. The stress-strain data of tested steel wires correlated well with recently developed high-strength steel wire material models at elevated temperatures. The wire rupture surfaces indicated a brittle failure at ambient temperature and a ductile failure with visible necking under fire conditions. The ultimate (rupture) strain capacity of steel wires decreased from 5% to almost 1% during fire tests. Further, the post-fire strength of PWS cable was unchanged but the elasticity modulus increased by 19% and the rupture strain decreased by 20%. The experimental findings indicate the necessity of fire protection application on PWS cables to keep cable temperatures below the critical temperature of 400 degrees C in a fire hazard.