Post-fire mechanical properties of low-relaxation hot-dip galvanized prestressed steel wires

摘要

Low-relaxation hot-dip galvanized prestressed steel wires are the basic component materials of high-strength steel cables, which have wide applications as key load-bearing members in prestressed steel structures. Provided that the general appearance of the prestressed steel structure is acceptable after a fire event, how the behaviors of the steel cables in these structures have been affected must be estimated accurately to ensure safety. Therefore, a series of experiments with a total of 360 specimens was conducted to investigate the post-fire mechanical properties of low-relaxation hot-dip galvanized prestressed steel wires with various grades, namely, 1670, 1770, 1860, and 1960. Tensile coupon tests were performed on specimens after exposure to 13 preselected temperatures up to 1000 degrees C, where two different cooling methods, namely, air cooling and water cooling, were considered. The post-fire stress strain curves, elastic moduli, yield strengths, ultimate strengths, and ductility were obtained. Additional tests were also conducted to study the effects of cyclic heating-cooling. The post-fire mechanical properties of the studied steel wires changed significantly after exposure to temperatures exceeding 400 degrees C, and the change characteristics of different steel wire grades were similar. Moreover, the influences of different cooling methods were notable: the water-cooled steel wires lose most of their ductility and strength when the exposure temperature exceeded 700 degrees C; whereas the effects of cyclic heating-cooling were insignificant. Thus, predictive equations that incorporate the influences of different cooling methods were developed to evaluate the post-fire mechanical properties of the steel wires studied.