Effects of load rate, heating rate, and creep on the ultimate strength and rupture of A416 7-wire strand at elevated temperature

Abstract

Tensile testing was performed on ASTM A416 cold-drawn 7-wire strands under varying combinations of applied loading and high temperature in three phases: “steady-state” tests, for which increasing load is applied to a specimen at steady-state temperature; “transient” tests, for which the ambient specimen is initially loaded to a constant target tension value and the temperature is then increased until the specimen fractures; and “creep” tests, for which the specimen is subjected to a constant target combination of temperature and tensile loading for a prolonged period of time, during which it accumulates creep strains until fracturing. Temperature-induced decreases in ultimate strength and proportional limit are relatively consistent compared to the existing literature for a wide range of cold-drawn strands fabricated under different governing standards. Steady-state tests produced slightly more thermally induced strength loss compared to transient tests, which suggests that design-basis predictions that are founded on steady-state test results can be used to conservatively predict the thermally induced strength loss in strands that are increasingly heated during fire exposure. Strands loaded to a stress utilization ratio beyond 70 % of their thermally dependent ultimate strength can experience a significant increase in creep strain under prolonged thermal exposure.