Tensile and fatigue experiments on the post-fire performance of high-strength steel wires coupled with corrosion action

This study investigates the coupled effects of fire and corrosion on the mechanical performance of high-strength steel wires for bridge cables through tensile and fatigue tests after exposure to elevated temperatures. The specimens were 7 mm diameter steel wires with a strength grade of 1860 MPa. First, accelerated corrosion testing was conducted on seven groups of wires for durations of 0 to 90 days. Each group was then heated to one of six target temperatures (300-700 °C) under sustained tensile stress of 55.8 MPa (at 700 °C) or 93.0 MPa (below 700 °C). Tensile and fatigue tests were then performed to evaluate the influence of temperature and corrosion across all exposure combinations. Stress-strain curves from tensile testing provided four key mechanical properties: elastic modulus ( E ), yield strength ( f y ), ultimate strength ( f u ), and ultimate strain ( δ u ). Fatigue tests at 300 °C, 500 °C, and 700 °C employed a constant stress range of 360 MPa and a frequency of 10 Hz. Prediction models for residual strength and fatigue life were developed and calibrated against experimental data, integrating the effects of temperature and corrosion. With increasing corrosion duration, the wire surfaces darkened from brown to black. Tensile tests revealed more pronounced necking in specimens exposed to higher temperatures. The elastic modulus ( E ) remained virtually unaffected by corrosion duration or temperature. Corrosion significantly reduced f y and f u , while increasing δ u . At temperatures lower than 300 °C, f y , f u , and δ u remained nearly constant compared to their values at 20 °C. However, after corrosion exposure, these indicators at 300 °C were 3.0%, 5.5%, and 19.4% lower than those of uncorroded specimens at the same temperature. The reduction in f y and f u increased with temperature, reaching maxima of 10.5% and 10.9%, whereas the reduction in δ u showed no clear correlation with temperature. Fatigue life decreased with increasing corrosion severity, and a strong negative correlation was observed between corrosion rate and fatigue life.An increase in corrosion rate from 6.34% to 13.76% resulted in a 77.8% reduction in fatigue life. Elevated temperatures also accelerated fatigue degradation, with a maximum life reduction of 82.4% at 700 °C. Based on the tensile and fatigue experimental results, theoretical models were established by Rational Taylor equation, which have provided reliable predictions (R² > 0.95) for the residual strength and fatigue life of steel wires under coupled fire-corrosion conditions.