For investigating effect of heating and cooling process simulating fire damage on mechanical properties of steel used in aged bridges, a series of experiment was carried out. The contents of carbon, sulfur and copper of steels extracted from actual aged bridges were more than those of present general steels. Heating up to 600℃ and water-cooling made the yield stress and ultimate strength of steels higher than those without heating and cooling. The reason of this phenomenon might be solute strengthening by carbon and copper. However, it might not affect the soundness of bridge member subjected to fire.
