Mechanical properties of prestressing steel in and after fire

Abstract

The mechanical properties of prestressing steel at elevated temperatures and after cooling are essential to the fire resistance design and post-fire evaluation of residual load-carrying capacity of prestressed concrete structures. Experiments were carried out by an accurate testing system for development of empirical formulae to predict the deterioration of prestressing steel at elevated temperatures and after cooling. The helical structure of the commonly used 7-wire strands allows estimation of mechanical properties of the strand based on that of the central wire. Hence only the central wire of strand was tested, which enabled better clamping and control, and hence more accurate measurements. Grade 1860 strands to GB/T 5224 mostly used in Mainland China and Grade 1860 strands to BS 5896 used in European and other countries were tested. Consistent models for reduction factors for various properties were developed. Some strands extracted from prestressed concrete specimens after fire testing were also tested for verification.