Statistical analysis of reinforcing steel properties
Degree GrantorUniversity of Canterbury
Degree NameMaster of Engineering
The previous Grade 275 and Grade 380 reinforcing steels have been respectively replaced by Grade 300 and Grade 430 steels confirming to the new standard NZS 3402, released in December 1989. Grade 300 is similar to, but a little stronger than, the previous Grade 275. Grade 430 has a significantly higher yield strength, lower strain hardening rate and is more ductile and readily weldable when compared to the old Grade 380. This project was carried out to investigate the distribution of mechanical properties for NZS 3402 Grade 300, and the micro-alloyed Grade 430 reinforcing steel manufactured by Pacific Steel Ltd. The investigation was based on data supplied by Pacific Steel Ltd and on data generated from mechanical tests carried out in the Materials Laboratory of the Mechanical Engineering Department, University of Canterbury. Tensile testing was carried out on the supplied material in the as rolled (deformed reinforcing bar) condition and on standard tensile specimens machined from these bars. One machined tensile specimen was pre-strained 5% and artificially aged to determine a strain ageing index for each cast supplied. For both grades of steel distributions of lower yield strength, tensile strength, elongation at fracture, Luder strain at the yield point, strain hardening parameters n and k, and three parameters measuring strain ageing index were determined. The characteristic yield strength, minimum and maximum yield strength ranges obtained were found to comply with the specified tensile properties in the new specification. Multiple linear regression techniques were used to investigate relationships between the determined mechanical properties and the steels chemical composition as determined by Pacific Steel Ltd. The regression analysis yielded simple linear equations which can be used to predict the mechanical properties of bars from production variations in chemical composition. These equations reveal that the improved properties of Grade 430 reinforcing steel is mainly attributed to the addition of 0.04% vanadium. Grade 430 steel is found to be less susceptible to strain ageing and can be used in plastic hinge zones in reinforced concrete structures.