Modeling mechanical properties of prestressing steel strand at elevated temperature

The purpose of this paper is to model mechanical properties of prestressing strand at elevated temperature for estimating the strength and deflection of prestressed concrete members during fire and/or after fire. Prestressing strands(SWPR7BL) of 12.7 mm in diameter were used as test coupons. Tensile tests on prestressing strands at elevated temperatures were conducted to investigate mechanical properties such as yield strength, Young's modulus and creep strain. Reduction in yield strength, Young's modulus and stress-strain curves at elevated temperature were formulated. Creep tests were conducted on prestressing strands. The initial stress applied was 70% of the yield strength. The maximum creep strain was as large as 545 microns at 250°C. Creep behavior of presstressing strands was approximated by a numerical formula proposed by Norton and Bailey. Using the formula together with time-hardening rule, an estimation method of relaxation of prestressing steel at high temperatures was proposed.