Variability of Mechanical Properties of Reinforcing Bars

The results of approximately 4000 published and unpublished tensile tests on deformed reinforcing bars are studied to obtain statistical relationships for various mechanical properties. The sample included No.3 through No.18, Grades 40 and 60, bars. The means and coefficients of variation of the mill test yield strengths were found to be 48.8 ksi (337 MN/m²) and 10.7% for Grade 40 and 71 ksi (MN/m²) and 9.3% for Grade 60 bars. Beta distributions were used to represent both of these sets of data. The static yield strength was found to be 3.5 ksi (24 MN/m²)) lower on the average than the mill test yield strength in both cases, with a coefficient of variation of 13.4%. The trend to lower yield strengths with increased bar sizes observed early in the 1970's was not present in more recent test data, apparently due to more stringent production control in recent years.