Variability of Mechanical Properties and Reliability of Thermo Mechanically Treated Reinforcements in Nigeria

Abstract

Thermo Mechanically Treated (TMT) reinforcements from different
manufacturers in Nigeria were subjected to tensile strength tests to
determine the variability of their yield strength, ultimate tensile strength,
and ductility. For the 70 samples tested, 91.5% met the required
characteristic strength of 500 MPa, and the percentage elongation at
fracture satisfied all the requirements of BS 4449:2005. The probability
distribution of the yield strength of the TMT reinforcements were found to
conform better to normal distribution with a Chi-Square value (X2
) of 4.342
against lognormal and Weibull distribution, with Chi-Square values of
4.80 and 6.536 respectively. The mean yield strength of the samples was
found to be 532.8 MPa with a standard deviation of 24.926 MPa, and
coefficient of variation of 4.678%. The probability of the samples tested
falling below the yield strength of 500 MPa was found to be 9.4% with a
reliability index of 1.316. The ultimate tensile strength to yield strength
ratio (Rm/Re) was found to be averagely high (with a mean of 1.356 and a
standard deviation of 0.095) when compared to the requirements of BS
4449:2005 and test results from other parts of the world. This was the
major source of non-conformity to the requirements of BS 4449:2005.