Experimental research on the mechanical properties of prestressing steel wire ( f_ptk = 1770 N/mm², d = 5 mm, low relaxation) at and after high temperature

The mechanical properties of prestressing steel wire at and after high temperature are the key factor in the design of fire resistance and after-fire damage evaluation of prestressed structures. A tensile experiment of 16 prestressing steel wires( f_ptk = 1770 N/mm², d = 5 mm, low relaxation of stress) at high temperature and a tensile experiment of 14 prestressing steel wires after high temperature were carried out. According to the experiment, the shapes of stress-strain curves of steel wire at high temperature become smooth and the mechanical property indexes of the steel wire such as strength, modulus of elasticity, etc. degenerate continuously as temperature increases. According to the experiment after high temperature, the mechanical property of steel wire varies little when the highest temperature that the steel wire reaches is less than BOOT); while the stress-strain curves of steel wire become more ductile and the mechanical property indexes of the steel wire degenerate gradually when the highest temperature is more than 300°C. By applying the theory of viscoelastic mechanics, stress-strain curves of steel wire at high temperature without loading speed influence are obtained. Laws of mechanical property indexes of the wire at high temperature and after high temperature are presented. The mathematic models of the stress-strain relationship of the prestressing steel wire at and after high temperature are established. All can be served as basic data for the analysis of fire resistance and after-fire damage evaluation of prestressed structures.