The objective of the research is to analysed the yield strength of steel on bridge
construction, through comparing manual estimating method and minitab program version 13, with
reliability about 95% and 99%. Comparison of results is doing by manual estimating aproach,
wich is results of mean samples, standard deviation of samples, and estimating interval of mean
population, and by minitab program version 13 is, normality test and quick count with reliability
95% and 99%. Research is doing with a small number of samples procedure (n<30), and
diameters (Ø) of samples is 10 mm, 16 mm, 19 mm, and 22 mm. Based on technique of analysis,
there’s different achievement that compares the results of ultimit yield strength of steel by the
methode of point estimating and estimating interval. Estimating of confidence intervals or ci =
95%, about 0.001% to 0.239%, and estimating of confidence intervals for ci = 99%, about 0.002%
to 0.550%, and finally the difference between area of yield strength with confidence intervals or ci
= 99% and 95% is about 0.001% to 0.315%
