Experimental study on the post-fire mechanical properties of high-strength steel tie rods

• Post-fire mechanical properties of four grades of steel tie rods were obtained.
• Mechanical properties significantly changed after exposure to certain temperatures.
• The influences of two different cooling methods were significant.
• The effects of cyclic heating and cooling were insignificant.
• Predictive equations were proposed to evaluate the post-fire mechanical properties.

High-strength steel tie rods have been increasingly used as important load-bearing members in building structures. During fire hazards, building structures are inevitably exposed to elevated temperatures. If the general appearance of the structure is satisfactory after a fire event, how the performance of steel tie rods in these building structures has been affected should be accurately estimated. Hence, an experimental investigation was conducted to reveal the post-fire mechanical properties of four widely used high-strength steel tie rod grades, namely, GLG460, GLG550, GLG650, and GLG835. Specimens were heated to 13 various preselected temperatures up to 1000 °C and subsequently cooled down to ambient temperature via two different methods: air cooling and water cooling. Tensile coupon tests were conducted, and the post-fire stress–strain curves, elastic modulus, yield strengths, ultimate strengths, and ductility were obtained. Additional tests were also conducted to investigate the effects of cyclic heating and cooling. The post-fire mechanical properties of high-strength steel tie rods significantly changed after exposure to temperatures exceeding approximately 650 °C, and the change characteristics were much different from that of hot-rolled steels and cold-formed steels. The influence of different cooling methods was notable, whereas the effects of cyclic heating and cooling were insignificant. Thus, new predictive equations, where the influence of different cooling methods was incorporated, were proposed to evaluate the post-fire mechanical properties of steel tie rods.